Dan Chujko & Associates, L.L.C.

Lighting 101

Just as no show, function or event that is reproduced is exactly the same, there is no one proper way to light an event or performance area. Think about all of the different types of events or performances that exist: concerts, dramas, lectures, industrials, product launches, operas, musicals, etc... Now imagine all of the settings or locations where these functions will take place: hotels, auditoriums, churches, warehouses, manufacturing plants, tents, theatres, arenas and/or outdoors. Fortunately, there are some simple lighting design techniques that can help anyone provide appropriate lighting for their productions. These guides will give you a basic overview of the industry buzz words, ideas,and techniques used to light an event or performance.

Topics

Basic Theory of Lighting	Quantity, Quality, Efficiency
Color Metrics	Useful Formulas
Fixtures	Glare
Lighting Audits	Upgrading
HVAC Interaction	Disposal
Legislation	Software
Additional Information	Go to Glossary

How to color stage lighting to enhance the color in scenery, costumes, and makeup

Determining the effect of colored light on scenery and costumes

How to experiment with color on color

What shall we change?

Makeup and Light

Figure 1. The hard way with the color wheel

Figure 2. The easy way to mix colored light with costumes and scenery

Figure 3. Making up with colored lights

Figure 4. The effect of color on you

Basic Theory

Light Guide:
Principles of Light

Light is a form of radiant energy that travels in waves made up of vibrating electric and magnetic fields. These waves have both a frequency and a length, the values of which distinguish light from other forms of energy on the electromagnetic spectrum.

Visible light, as can be seen on the electromagnetic spectrum, represents a narrow band between ultraviolet light (UV) and infrared energy (heat). These light waves are capable of exciting the eye's retina, which results in a visual sensation called sight. Therefore, seeing requires a functioning eye and visible light.

Lighting Systems

Light can be produced by nature or by humans. "Artificial" light is typically produced by lighting systems that transform electrical energy into light. Nearly all lighting systems do so either by passing an electrical current through an element that heats until it glows, or through gases until they become excited and produce light energy.

Incandescent light sources are an example of the first method, called incandescence. Current is passed through a filament, which heats until it glows. Because this method is considered wasteful (most of the energy entering the lamp leaves it as heat instead of visible light, other light sources were pioneered that rely on the gaseous discharge method, including fluorescent, high-intensity discharge (HID) and low-pressure sodium light sources.

A typical lighting system is comprised of one or more of these light sources, called the lamps. Fluorescent, HID and low-pressure sodium lamps operate with a ballast, a device that starts the lamp and regulates its operation. Lamps and ballasts in turn are part of the luminaire, or light fixture, which houses the system and includes other components that distribute the light in a controlled pattern.

Designing the Lighting System

To produce a new lighting system in a construction or renovation scenario, it must be designed. The designer must determine desired light levels for tasks that are to be performed in a given space, then determine the light output that will be required to meet those objectives consistently, taking into account all the factors that degrade both light output and light levels over time. Equipment must then be chosen and placed in a layout to produce the desired light distribution. The designer must also consider a range of quality factors in his or her design choices and equipment selection, including color, minimizing glare, safety and if required, aesthetics.

Managing the Lighting System

To properly manage an existing system, many types of professionals may be involved, from electrical contractors to facilities manager - - for our purposes in this case, we will call them lighting managers. The lighting manager must ensure that the existing lighting system consistently provides the most effective lighting at the lowest operating and maintenance cost. This may entail retrofitting or upgrading the system to reduce energy costs and/or increase performance, a planned maintenance program to keep the system operating at peak performance, and other activities that will ensure that the lighting system is continuously doing its job.

Light Guide:
Lighting Metrics: Quantity, Quality, Efficiency

Because some 85% of human impressions are visual, proper quantity and quality of light are essential to optimum performance. The mission of lighting management is to provide the optimum quantity and quality of light to its users at the lowest operating cost.

Lighting metrics are used to understand and predict how a lighting system will operate. They deal with quantity of light (light output and light levels), quality of light (brightness and color), and fixture efficiency (electrical efficiency and how much light leaves the fixture).

QUANTITY OF LIGHT

Luminous Flux (Light Output). This is the quantity of light that leaves the lamp, measured in lumens (lm). Lamps are rated in both initial and mean lumens.

Initial lumens indicate how much light is produced once the lamp has stabilized; for fluorescent and high-intensity discharge (HID) lamps, this is typically 100 hours.

Mean lumens indicate the average light output over the lamp's rated life, which reflects the gradual deterioration of performance due to the rigors of continued operation; for fluorescent lamps, this is usually determined at 40% of rated life.

A number of factors affect a lamp's light output over time, including lamp lumen depreciation, the lamp's interaction with the ballast, supply voltage variations, dirt or dust on the lamp, and the ambient temperature in the fixture.

To avoid confusion, note that "lumen output" is a term also used to describe a fixture's light output, not just a lamp's. Even more factors can affect light output in this case, including the distribution characteristics of the fixture, fixture surface depreciation, and dirt and dust buildup.

Illuminance (Light Level). This is the amount of light measured on the workplane in the lighted space. The workplane an imaginary horizontal, tilted or vertical line where the most important tasks in the space are performed. Measured in footcandles (fc) (or lux in metric), light levels are either calculated or, in existing spaces, measured with a light meter. A footcandle is actually one lumen of light density per square foot; one lux is one lumen per square meter. Like lumens, footcandles can be produced as either initial or maintained quantities.

Initial footcandles indicates a light level after new lamps are installed.

Maintained footcandles indicates a light level after light loss factors are considered over a period of time. Light loss factors include those affecting light output (see above) and also room surface reflectances, room size/proportions, dirt and dust buildup. While light output may describe either the output of a light source or fixture, maintained footcandles always takes into account the efficiency of the fixture in transmitting light to the workplane.

The human eye is a sophisticated piece of machinery; it is able to adjust to a wide range of light levels, including about 10,000 footcandles on a sunny day to about 0.01 footcandles under full moonlight. However, optimum ranges of light levels have been established for various tasks so that those tasks are performed most efficiently (reading a magazine, for example, would be difficult under moonlight, while 10,000 footcandles would be excessive).

For more information, see Lighting Design Basics and Light Loss Factors.

QUALITY OF LIGHT

Luminance (Photometric Brightness). The light that we actually see, brightness can be measured as the light leaving a lamp, or the light reflecting from an object's surface. If not controlled, brightness can produce levels of glare that either impair or prevent a desired task being performed. Glare can be described as direct or reflected glare, which can then result in discomfort or disability.

Direct glare comes straight from the light source.

Reflected glare shows up on the task itself, such as a computer screen.

Discomfort glare does not prevent seeing makes it uncomfortable.

Disability glare prevents vision. A popular example is holding a glossy magazine at a certain angle; a veiling reflection results, impairing our reading of the page.

Color. The color quality of a lamp is revealed as its color temperature rating and Color Rendering Index (CRI) rating. For a detailed description of these metrics, see Color Metrics.

FIXTURE EFFICIENCY

There are two ways to look at a light fixture's (luminaire's) efficiency; one indicates how well the lighting system transforms electrical input into useful light output, and the other indicates how well the fixture itself transmits light from the lamp(s) to the workplane.

Electrical Efficiency. Lighting systems require electrical input to work. This input is measured in watts (W), a measure of required electric power. A lighting system's rated input wattage, therefore, is the amount of power required for it to work at any given instant of time.

Lamp manufacturers publish nominal wattage ratings for their lamps; when fluorescent and HID lamps are operated as a system with a ballast, however, a new rated wattage will result, published by the ballast manufacturer. Ballast manufacturers publish up to three input wattage ratings. The ANSI number is the result of a standardized ANSI test of that given ballast manufacturer's ballast operating a given compatible lamp type (often called the "bench test" because the lamps and ballasts are operated bare on a bench). The next one or two are the manufacturer's ratings for tests in actual open and/or enclosed fixtures.

While the manufacturer's ratings can be considered more realistic (because the testing takes place closer to actual field conditions), the ANSI number should be used when comparing different ballasts because it reflects the results of a common, standardized test procedure.

Therefore, one way to compare the electrical efficiency of lamp-ballast systems is to determine a common light output level, then compare the input wattage for various systems.

A more popular way of achieving a comparison of the relative efficiencies of lighting systems is to use efficacy, expressed in lumens per watt (LPW or lm/W). To determine a system's efficacy, divide its lumen output by its rated input wattage.

When lighting professionals apply the results of efficiency to actual system operation (usually to determine the operating cost savings of a retrofit, they need to determine the amount of energy the lighting system consumes, not just its input wattage. To calculate the energy use of a lighting system, multiply input wattage (W) x time (hours of operation during a year).

Example for Lighting System:

Input Wattage	100W
Lumen Output	10,000 lm
Efficacy	100 LPW	10,000 lm ÷ 100W
Hours of Operation	3,120 h	5 days/week x 12 hours/day x 52 weeks/year
Energy Use	312,000 Wh	100W x 3,120 hrs/year
Energy Use	312kWh	312,000 watt-hours (Wh) ÷ 1,000 = 312 kilowatt-hours (kWh)
Utility Charge/kWh	$0.075
Energy Cost/Year	$23.40	312kWh x $0.075/kWh

For more information, see Retrofit Economics.

Fixture Efficiency. The light fixture's physical characteristics will affect how much light will leave the fixture and how much will be directed at the task. Factors that affect the efficiency of the fixture include its shape, the reflectance of its materials, how many lamps are inside the fixture (and how close they are to each other), and whether shielding material such as a lens or louver is used to soften or scatter the light.

To compare fixture efficiencies in a given environment, designers often use a derating factor called the coefficient of utilization (CU). This value shows the percentage of lumens produced by the lamps that reach the workplane after light is lost due to the fixture's efficiency at transmitting light, the room proportions, and the ability of room surfaces to reflect light. Determining the most accurate CU value for various fixtures in a new or renovation space requires use of the Zonal Cavity Method. For more information about CU values for generic fixture types, see the latest edition of the Illumination Engineering Society of North America IESNA Lighting Handbook.

The National Lighting Collaborative has developed the Luminaire Efficacy Rating, or LER, part of a voluntary program being implemented by the lighting industry. A free publication is available describing the LER.

Light Guide:
Color Metrics

Basic Principles

Light, like all forms of radiant energy, is represented on the electromagnetic spectrum. Traveling in waves, light is differentiated from other forms of radiant energy such as heat and X-rays by the frequency and length of its waveform. A narrow band on the spectrum is visible light, composed of different colors/wavelengths, from violet at 380 nanometers to red at 620-760 nanometers. An even balance of these light waves composes white visible light. To see this principle firsthand, look at a rainbow, which results from sunlight being refracted by droplets of moisture in the air, or simply shine a beam of white light through a glass prism to make a rainbow of colors appear on the other side.

Visible light cannot be seen, however. If we turned on a flashlight in a dark room, the beam of light we are seeing is actually light being reflected from a multitude of dust particles in the air. Therefore, we see objects only when light is reflected or emitted from them. And that is how we see color.

All objects are chemically oriented to absorb certain wavelengths of light and reflect others. The ones that are reflected are perceived by the human eye to be the color of the object. A red object being struck by visible white light will absorb all wavelengths except red, which is reflected, and so we see the object as red. A pure white object reflects all wavelengths and absorbs none. A pure black object absorbs all wavelengths and reflects none.

This is where a great amount of art comes into lighting because few lamp types produce pure white light. Some lamps produce light that is saturated in blue and green, others red and yellow. A red object struck by light that contains only blue and green wavelengths would not appear red as if it were under sunlight. A low-pressure sodium lamp produces light saturated in yellow, which means that all objects struck by it will appear yellow, black or a shade of gray. The major lamp manufacturers all have literature and exhibits that demonstrate the effect of light on color. The slogan of one: "Color is how you light it."

Metrics

To understand how a lamp's light will affect the color of objects in the space, three metrics are used, including spectral power distribution, color temperature and color rendering.

Spectral power distribution shows the visible light spectrum and the wavelength composition for the light from the lamp (see illustration). The spikes indicate that the light is stronger in revealing certain colors.

A spectral power distribution curve for a 400K lamp with a triphosphor (red, blue, green) coating to improve color rendering. Courtesy of Osram Sylvania

Color temperature, expressed on the Kelvin scale (K), is the color appearance of the lamp itself and the light it produces.

According to the Illuminating Engineering Society of North America (IESNA), color temperature is "the absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source."

Imagine a block of steel that is steadily heated until it glows first orange, then yellow and so on until it becomes blue or bluish-white. At any time during the heating, we could measure the temperature of the metal in Kelvins (Celsius + 273) and assign that value to the color being produced, resulting in a "color temperature." Computer software performs this function for today's lamps, giving them a color temperature rating found in the manufacturers' literature.

For incandescent lamps, the color temperature is a "true" value; for fluorescent and high-intensity discharge (HID) lamps, the value is approximate and is therefore called correlated color temperature. In the industry, both terms - - color temperature and correlated color temperature - - are often used interchangeably. The color temperature of lamps makes them visually "warm," "neutral" or "cool" light sources.

Lamps with a lower color temperature (3500K or less) have a warm or red-yellow/orangish-white appearance. The light is saturated in red and orange wavelengths, bringing out warmer object colors such as red and orange more richly.

Lamps with a mid-range color temperature (3500K to 4000K) have a neutral or white appearance. The light is more balanced in its color wavelengths.

Lamps with a higher color temperature (4000K or higher) have a cool or bluish-white appearance. Summer sunlight has a very cool appearance at about 5500K. The light is saturated in green and blue wavelengths, bringing out cooler object colors such as green and blue more richly.

These three photos simulate the effects of color temperatures on objects. (Left) a warm light source is used, enhancing reds and oranges while dulling blues and greens; (Middle) a neutral source is used; (Right) a cool source is used enhancing blues and greens while dulling reds and oranges. Courtesy of Osram Sylvania

Once a color temperature is specified, use the spectral power distribution data to aid in selecting a specific lamp.

Color rendering, expressed as a rating on the Color Rendering Index (CRI), from 0-100, describes how a light source makes the color of an object appear to human eyes and how well subtle variations in color shades are revealed. The higher the CRI rating, the better its color rendering ability.

According to the IESNA, color rendering is the "measure of the degree of color shift objects undergo when illuminated by the light source as compared with the color those same objects when illuminated by a reference source of comparable color temperature."

Imagine two objects, one red, one blue, that are lighted by a cool light source with a low CRI. The red object appears muted while the blue object appears a rich blue. Now take out the lamp and put in a cool light source with a high CRI. The blue object still appears a rich blue, but the red object appears more like its true color.

Standard incandescent lamps enjoy a CRI rating of 100. Fluorescent lamps are in the 52-95 range, depending on the lamp. Advances in phosphor technology have enabled fluorescent and HID lamps to advance greatly in color rendering.

As stated in the IESNA definition, to compare any two given lamps, they must have the same color temperature for the comparison to have any meaning.

Specifying Color

When specifying color characteristics for a lamp, numerous psychological factors must be considered depending on the lighting goals for the space. Here are a few general tips.

Warm light sources are generally preferred for the home, restaurants and retail applications to create a sense of warmth and comfort, while neutral and cool sources are generally preferred for offices and similar applications to create a sense of alertness.

In addition, in retail applications, color is a critical design decision because buyers need to be able to choose products of the correct color, both to enhance the chance of its sale and to reduce the chance of it being returned once the buyer gets outside and sees it under sunlight. In this or any other application where the occupant needs to see the right color, good color quality is essential.

In other applications such as parking lots, color is not an important factor, so low-color-rendering lamps can be specified.

Light Guide:
Useful Formulas

ELECTRICAL FORMULAS

Demand for Power (kW) = System Input Wattage (W) ÷ 1,000

Energy Consumption (kWh) = System Input Wattage (kW) x Hours of Operation/Year

Hours of Operation/Year = Operating Hours/Day x Operating Days/Week x Operating Weeks/Year

Lighting System Efficacy (Lumens per Watt or LPW) = System Lumen Output ÷ Input Wattage

Unit Power Density (W/sq.ft.) = Total System Input Wattage (W) ÷ Total Area (Square Feet)

Watts (W) = Volts (V) x Current in Amperes (A) x Power Factor (PF)

Voltage (V) = Current in Amperes (A) x Impedance (Ohms) [Ohm's Law]

ECONOMIC FORMULAS

Simple Payback on an Investment (Years) = Net Installation Cost ($) ÷ Annual Energy Savings ($)

5-Year Cash Flow ($) = 5 Years - Payback (Years) x Annual Energy Savings ($)

Simple Return on Investment (%) = [Annual Energy Savings ($) ÷ Net Installation Cost ($)] x 100

DESIGN FORMULAS

Footcandles & Lumens

Footcandles (fc) = Total Lumens (lm) ÷ Area in Square Feet

1 Lux (lx) = 1 Footcandle (fc) x 10.76

Lux = Total Lumens ÷ Area in Square Meters

Calculating Light Level at a Point

For planes perpendicular to the direction of candlepower (Inverse Square Law):

Footcandles (fc) = I ÷ D²

I = Candlepower in candelas (cd)
D = Direct distance between the lamp and the point where light level is calculated

Many workplanes are not perpendicular to the direction of light intensity, which is why calculating light level at a point is useful for such applications. In these cases, we often must determine light levels on workplanes that are not horizontal and perpendicular but tilted or even vertical. For tilted-horizontal or vertical planes:

Horizontal Footcandles (fc_h) = (I ÷ D²) x H

Vertical Footcandles (fc_v) = (I ÷ D²) x L

I = Candlepower in candelas (cd)
D = Direct distance between the lamp and the point where light level is calculated

H = Distance between the lamp and the point direct below on the workplane

L = Distance between that point and the point where light level is being calculated

D = Square Root of (H² + L²) or D² = H² + L²

Calculating Average Light Level Throughout a Space (three formulas)

Average Maintained Illumination (Footcandles) = (Lamps/Fixture x Lumens/Lamp x No. of Fixtures x Coefficient of Utilization x Light Loss Factor) ÷ Area in Square Feet
Average Maintained Illumination (Footcandles) = (Total Lamps x Lumens/Lamp x Coefficient of Utilization x Light Loss Factor) ÷ Area in Square Feet

Average Maintained Illumination (Footcandles) = (Lamps in One Fixture x Lumens/Lamp x Coefficient of Utilization x Light Loss Factor) ÷ Area in Square Feet/Fixture

Lumen Method

Required Light Output/Fixture (Lumens) = (Maintained Illumination in Footcandles x Area in Square Feet) ÷ (Number of Fixtures x Coefficient of Utilization x Ballast Factor x Light Loss Factor)

Light Loss Factors (more on Light Loss)

Light Loss Factor (LLF) = Ballast Factor x Fixture Ambient Temperature Factor x Supply Voltage Variation Factor x Lamp Position Factor x Optical Factor x Fixture Surface Depreciation Factor x Lamp Burnouts Factor x Lamp Lumen Depreciation Factor x Fixture Dirt Depreciation Factor x Room Surface Dirt Depreciation Factor

Lamp Burnout Factor = 1 - Percentage of Lamps Allowed to Fail Without Being Replaced

Zonal Cavity Method (determining cavity ratios)

Room Cavity Ratio (for regular rooms shaped like a square or rectangle) = [5 x Room Cavity Depth x (Room Length + Room Width)] ÷ (Room Length x Room Width)
Room Cavity Ratio (for irregular-shaped rooms) = (2.5 x Room Cavity Depth x Perimeter) ÷ Area in Square Feet

Ceiling Cavity Ratio = [5 x Ceiling Cavity Depth x (Room Length x Room Width)] ÷ (Room Length x Room Width)

Floor Cavity Ratio = [5 x Floor Cavity Depth x (Room Length x Room Width)] ÷ Room Length x Room Width

Room surface reflectances can be predicted in a new design or measured in an existing facility. If existing facility:

Room Surface Reflectance (%) = Reflected Reading ÷ Incident Reading
Reflected Reading = Measurement from a light meter holding it about 1.5 feet away from the surface with the sensor parallel and facing the surface.

Incident Reading = Measurement from a light meter held flat against the surface and facing out into the room.

Calculating Number of Lamps And Fixtures And Spacing

Required No. of Fixtures = (Lumens/Lamp x No. of Lamps x Coefficient of Utilization x Light Loss Factor x Area in Square Feet) ÷ (Lumens/Lamp x Lamps/Fixture x Coefficient of Utilization x Light Loss Factor)

Required Lamps = Required Lumens ÷ Initial Lumens/Lamp

Maximum Allowable Spacing Between Fixtures= Fixture Spacing Criteria x Mounting Height

Fixture Spacing Criteria: See the manufacturer's literature
Mounting height: Distance in feet between the bottom of the fixture and the workplane

Spacing Between Fixtures = Square Root of (Area in Square Feet ÷ Required No. of Fixtures)

Number of Fixtures to be Placed in Each Row (N_row) = Room Length ÷ Spacing

Number of Fixtures to be Placed in Each Column (N_column) = Room Width ÷ Spacing

For the above two formulas, round results to the nearest whole integer.

Spacingrow = Room Length ÷ (Number of Fixtures/Row - 1/3)

Spacingcolumn = Room Width ÷ (Number of Fixtures/Column -1/3)

If the resulting number of fixtures does not equal the originally calculated number, calculate impact on the designed light level:

% Design Light Level = Actual No. of Fixtures ÷ Originally Calculated No. of Fixtures

To calculate fixtures mounted in continuous rows:

Number of Luminaires in a Continuous Row = (Room Length ÷ Fixture Length) - 1

Number of Continuous Rows = Total Number of Fixtures ÷ Fixtures Per Row

MAINTENANCE

Lamp Life

Calendar Lamp Life (Years) = Rated Lamp Life (Hours) ÷ Annual Hours of Operation (Hours/Year)

Lamp Burnout Factor

Lamp Burnout Factor = 1 - Percentage of Lamps Allowed to Fail Without Being Replaced

Group Relamping Cost

Annualized Cost ($) = A x (B + C)

A = Operating Hours/Year ÷ Operating Hours Between Relampings

B = (Percentage of Lamps Failing Before Group Relamping x Number of Lamps) x (Lamp Cost + Labor Cost to Spot Replace 1 Lamp)

C = (Lamp Cost, Group Relamping + Labor Cost to Group Relamp 1 Lamp) x Number of Lamps

Spot Relamping Cost

Average Annual Cost ($) = (Operating Hours/Year ÷ Rated Lamp Life) x (Lamp Cost + Labor Cost to Replace 1 Lamp) x Total Number of Lamps

Cleaning Cost

Cleaning Cost ($) = Time to Wash 1 Fixture (Hours) x Hourly Labor Rate ($) x Number of Fixtures in Lighted Space

ENVIRONMENTAL IMPACT

Average Reduced Air Pollution (lbs. Carbon Dioxide) = Energy Savings (kWh) x 1.6 lbs.

Average Reduced Air Pollution (g. Sulphur Dioxide) = Energy Savings (kWh) x 5.3 g.

Average Reduced Air Pollution (g. Nitrogen Oxides) = Energy Savings (kWh) x 2.8 g.

Pounds = Grams ÷ 454

Tons = Pounds ÷ 2,000

Light Guide:
Light Source and Fixture Selection

The lighting design process in its most basic form entails identifying a task and then providing a light source that will provide proper quantity and quality of light for the task. The fixture protects the light source, connects it to the power source and distributes its light. In this article, we will review the basic factors that go into specifying a light source and a fixture.

Light Source Specification Checklist

The light source is the actual light-producing component of the lighting system. It may operate simply as a lamp (incandescent/halogen) or as a lamp powered by a ballast (fluorescent and high-intensity discharge [HID]).

Below are considerations for specifying three basic lamp types:

Incandescent Lamps

Do not require a ballast
Warm color appearance with a low color temperature and excellent color rendering (CRI 100)
Compact light source
Simple maintenance due to screw-in Edison base
Less efficacious light source
Shorter service life than other light sources in most cases
Filament is sensitive to vibrations and jarring
Bulb can get very hot during operation
Must be properly shielded because incandescent lamps can produce direct glare as a point source
Require proper line voltage as line voltage variations can severely affect light output and service life

Fluorescent Lamps

Require a ballast
Range of color temperatures and color rendering capabilities
Low surface brightness compared to point sources
Cooler operation
More efficacious compared to incandescent
Ambient temperatures and convection currents can affect light output and life
All fixtures installed indoors must use a Class P ballast that disconnects the ballast in the event it begins to overheat; high ballast operating temperatures can shorten ballast life
Options for starting methods and lamp current loadings
Requires compatibility with ballast
Low temperatures can affect starting unless a "cold weather" ballast is specified

HID Lamps

Require a ballast
Ambient temperature does not affect light output, although low ambient temperatures can affect starting, requiring a special ballast
Compact light source
High lumen packages
Point light source
Range of color temperatures and color rendering abilities depending on the lamp type
Long service life
Highly efficacious in many cases
Line voltage variations, possible line voltage drops, and circuits sized for high starting current requirements must be considered

Below is a checklist for specifying the right lamp for the application:

Light output
Input wattage
Efficacy (lumens per watt)
Rated service life
Size
Surface brightness
Color characteristics
Electrical operating characteristics
Requirement of additional equipment such as ballasts
Compatibility with the electrical system
Suitability for the operating environment

See also Fluorescent Light Sources, Incandescent Light Sources, HID Light Sources, Demanding Environments, Color Metrics, Industrial Light Source and Fixture Selection, Lighting Metrics

Light Fixture Specification Checklist

A luminaire, often called a light fixture, is a complete lighting unit that produces and distributes light. It contains the light source, a ballast if the lamp is fluorescent or HID, components designed to diffuse or distribute the light in a controlled pattern, components to protect and position the lamp(s), and a connection to the power source.

The light fixture's basic function is to produce and distribute light to fulfill the design goals for the lighted space. Below is a checklist for specifying the right fixture for the job.

Characteristics of The Space

First, the specifier must fully understand the demands of the application and conditions in the space that will affect the operation of the lighting system:

Tasks to be performed in the space
Desired light levels based on the tasks performed in the space
Room size and dimensions
Structural obstructions such as beams
Layout of furniture and obstructions such as partitions
Room and object surface colors and reflectances
Special concerns such as safety and security
Hours of operation
Assessment of normal operating conditions
Possibility or known existence of abnormal operating conditions
Cleanliness of the area during operation
Maintenance schedule
Availability of daylight

See also Lighting Audits, Demanding Environments, Planned Lighting Maintenance, Lighting Design: Basic Principles

Characteristics of Lighting Components And The Fixture

Now the most appropriate light source can be selected, followed by the fixture. The specifier must understand the factors affecting fixture selection:

Electrical, physical and operating characteristics of the light source selected
Electrical, physical and operating characteristics of appropriate ballasts
Electrical, physical and operating characteristics of controls to be employed
Fixture efficiency (% lamp light output transmitted out of the fixture)
Distribution pattern
Glare control
Finish
Appearance
Size
Accessibility of interior components for maintenance
Ability to handle abnormal as well as normal operating conditions
Aesthetics

See also Light Fixtures: Classifications, Lighting Metrics, Fixtures: Optical Systems, Lighting Design: Basic Principles, Industrial Light Source and Fixture Selection, Controlling Glare

Light Guide:
Optical Systems: Methods of Controlling Light

A luminaire, often called a light fixture, is a complete lighting unit that produces and distributes light to fulfill the design goals for the lighted space.

The primary methods of controlling light from a bare light source via a light fixture are reflection, transmission and refraction. Other methods include polarization, interference and absorption. In this article, we will discuss the first three.

Reflection

Reflection, the most common form of controlling light, occurs when light rays impact and are then reflected from a surface. The types of reflection include:

Specular
Diffuse
Spread
Selective

Specular reflection is when light is reflected from a highly polished surface such as smooth polished metal, producing a consistent angle.

Diffuse reflection is when light is reflected from a rough surface, producing a variety of angles depending on how the light impacts each tiny part of the rough surface. Diffuse reflection is typically used to minimize glare, hot spots and shadows.

Spread reflection is when light is reflected into a cone of light rays from surfaces such as corrugated or etched metal, plastic or glass.

Selective reflection is when a colored surface is used so that only certain color wavelengths or reflected as opposed to absorbed or transmitted.

As can be seen, how the reflecting surface is shaped determines how the beam is reflected. The most popular shapes for such surfaces include circular, parabolic, ellipsoidal and combination.

Transmission

Transmission occurs when light rays are passed through a material. The types of transmission include:

Direct
Diffuse
Spread
Selective

Direct transmission is when light rays go through the material with no change to their direction or color. Example: Clear plate glass.

Diffuse transmission is when light rays are widely spread, useful when we want to obscure the light source and produce a uniform appearance of light on the transmitting surface. Example: Inside-frosted glass.

Spread transmission is when the maximum intensity of light rays passed through with little change in direction, producing a glow on the transmitting surface and a sense of sparkle.

Selective transmission is when selected color wavelengths are allowed to pass through the material. Example: Colored glass.

Refraction

Refraction, used in prismatic lenses in fluorescent fixtures, floodlighting and streetlighting, occurs when light rays pass through one material and into another at a different intensity.

Light Guide:
Lighting Design: Basic Strategies

Light plays an essential role in our ability to perceive the world around us; the lighting system plays a critical role in how we perceive a space and can even influence how we act in that space. Lighting can affect performance, mood, morale, safety, security and decisions.

The first step in producing the right lighting design is to ask what the space is used for. The lighting designer can then determine quantity of light, color quality, brightness and direction.

It is beyond the scope of this article to go step by step through the process of producing a lighting design. Instead, we will review the several ways that lighting professionals look at lighting design, from the simple to the sophisticated.

Simple. One way is to ensure that the lighting system 1) provides ambient illumination for orientation and general tasks in the space, 2) task illumination for local, more demanding tasks, and 3) accent illumination to highlight special objects of interest or to guide occupants. An example of this scheme is an open office plan with workstations; we might provide indirect fixtures to provide ambient illumination, task lighting at the workstations for work, and accent lighting to highlight pieces of corporate art on the walls.

Standard. A typical general approach to lighting design is, after determining how the space is used, to provide general, localized general, localized and task illumination to meet these needs. General lighting provides a generally uniform light level on the workplane throughout the lighted space. Localized general lighting is similar but is tailored more to the location of tasks in the lighted space. Localized lighting, also called supplemental lighting, is used to provide light to a specific area. Task lighting delivers light tailored for a specific task.

Sophisticated. A final way of looking at lighting design is more sophisticated, focused not only on simply providing quantity of footcandles for tasks with accent illumination for highlighting, but also on the art of using light to produce a desired effect.

To explain this last approach, which deals with how the direction of light is controlled, let us start with an object.

Key Light. When we shine a light on an object from a single point source of light it is called key light; it highlights contours on the object and creates shadows; the exact effect depends on the angle of the beam of light. Most of the time we want to light the object to we can see its front. In these cases, the light source may be best place in front of and to the side of the object at an angle of 45°.

Fill Light. While this scene effects drama, for our purposes we will assume we need fill light. It can either be directional or diffused. In our example we could shine a directional light on the object from the opposite direction of the key light, softening or eliminating shadows depending on the strength of the fill light relative to the strength of the key light. We could also place fill light sources behind the object to light the entire room evenly. In the Figure below, we see the keylight supplemented by a single fill light.

Silhouetting. Suppose we wanted to emphasize the shape of the object as a silhouette. In this event, we would soften or even eliminate the key light and directional fill light, and instead provide only fill light, either intense or diffused, depending on the clarity of the silhouette and the drama we want to produce.

Uplighting. Suppose we wanted to uplight the object. The effect of uplighting is either very desirable or very undesirable because it is unusual. Effects range from intimate to eerie. A lot of landscape lighting includes uplighting to accentuate bushes and trees.

Sparkle And Glitter Effects. To add an atmosphere of elegance, we could add little lighting points of interest in the form of sparkle or glitter. This effect can be produced by either producing sharp reflections on specular surfaces in the room (sparkle), such as silverware in a restaurant, or by making the light source itself a source of interest (glitter) such as with a chandelier. Beware of glare in such cases.

Grazing And Washing Surfaces. On walls or on the surface of an object, we can change the way light impacts them so that we can produce different effects. Suppose we have a brick wall with a rough texture that we want to emphasize. We could graze the surface with light, meaning the light would strike the surface at a sharp angle. In this case, the light source would be mounted close to the wall. Now suppose the wall is smoother, and we want to emphasize that smoothness. We could wash the surface with light, meaning the light would strike the surface at a wider angle.

The selection of strategy or combination of strategies again will depend on how the space is used. In a retail environment, it might be desirable to provide strong keylighting to accentuate and dramatize key merchandise, while in an office such strong concentrations of accentlighting and shadowing might prove visually fatiguing. Uplighting may work well in an intimate restaurant or to highlight bottles of alcohol in a bar, but may make people look sinister in the home or office. Sparkle and glitter may work well in a restaurant, but might prove distracting in many industrial work areas.

Light Guide:
Light Loss Factors

When a light fixture is activated, it produces light which must leave the lamp, then the fixture, then reach the workplane where it is needed. Along the way, a number of operating and environmental conditions interfere with the transmission of light, resulting in wasted lumens. The lighting designer must provide a system that will take into account these conditions so that despite them the lighting system will provide proper quantity of light over time.

These conditions are captured as metrics called the light loss factors. Metrics are used to perform how something behaves. Light loss factors are captured as percentages or decimals (example: 0.95), which are then multiplied to result in a final Light Loss Factor in lighting calculations. There are two types of light loss factors, non-recoverable and recoverable.

Non-Recoverable Light Loss Factors

Some light loss factors are called "non-recoverable" because preventative maintenance generally does not affect the extent of the light loss. These include ballast factor, ambient fixture temperature, supply voltage variation, optical factor and fixture surface depreciation.

Ballast Factor

Lamps and ballasts experience losses when operating together as a system. The percentage of a lamp's initial rated lumens produced by a given ballast is called the Ballast Factor.

Ambient Fixture Temperature

This factor deals with fluorescent systems. Deviations above or below the ideal fixture operating temperature can affect the amount of light leaving the lamp.

Supply Voltage Variation

High or low voltages fed to lamps (incandescent) or ballasts (fluorescent and HID) from the building's power distribution can result in an increase or decrease of a lamp's lumen output. Electronic ballasts are not as sensitive to small variations in supply voltage as magnetic ballasts. Some models provide constant light output at +10% variation. The IESNA Lighting Handbook contains supply voltage variation data for various generic lamps; another source of information is the manufacturer's literature.

IOptical Factor

The amount of space lamps take up serves as an obstruction to light leaving the fixture that is reflected internally. Since lamps absorb mass, they absorb some of this light output. The result is what is called the Optical Factor. T12 lamps have an Optical Factor of 1. Removing lamps, or installing thinner-diameter T10 or T8 lamps, can result in a higher Optical Factor.

Fixture Surface Depreciation

As a fixture ages, its surfaces begin deteriorate. Blemishes absorb light instead of reflecting it; shielding materials may begin to discolor due to constant exposure to heat. This light loss factor is difficult to predict.

Recoverable Light Loss Factors

Some light loss factors are called "recoverable" because preventative maintenance can reduce the extent of the light loss. These include lamp burnouts, lamp lumen depreciation (LLD), fixture (luminaire) dirt depreciation (LLD) and room surface dirt depreciation (RSDD).

Lamp Burnouts

When a lamp expires, it becomes a "burnout." Lighting designers usually assume that the burnout will be replaced immediately. However, if it is known that a percentage of the lamps are burnouts at any given time, then a light loss factor must be reckoned with. For example, if 5% of the lamps are burnouts at any given time, then this light loss factor would be 0.95. Remember that 100% rated life is defined when 50% of the lamps in a large sample of lamps have failed.

Lamp Lumen Depreciation

As a lamp ages and nears end of life, it produces less and less light on a predictable curve, the extent of which depending on the type of lamp. If group relamping is employed as a planned maintenance strategy, then take the LLD factor for the point in life at which the lamps are replaced en masse. Otherwise, use an average, which is at 40% of life. See the Table below for typical LLD values for typical lamps.

Table. Typical LLD factors for several lamp types. Note that additional phosphor coatings to improve CRI in fluorescent lamps improves lumen maintenance.

F32T8, 85 CRI	0.91
F32 T8, 85 CRI	0.93
F96T12/CW "Slimline"	0.88
F96T12 "Slimline," 85 CRI	0.94
F96T12HO/CW	0.83
F96T12/HO, 85 CRI	0.90
Compact fluorescent	0.85
Mercury vapor	0.79
Metal halide	0.83
High pressure sodium	0.91

Fixture (Luminaire) Dirt Depreciation

Dirt and dust present in all ambient environments are ultimately attracted to and trapped in electrical equipment. The extent of dust collecting on the lamps depends on the environment, what type of fixture is in use, whether it is ventilated or not, and the type of work performed in the area. The extent of LDD depends on these conditions and also how often the fixtures will be cleaned. To determine this factor, first identify the fixture type's maintenance category (I through VI) in ascending order of imperviousness to dirt and dust intrusion (see the IESNA Lighting Handbook for more information).

An industrial strip fixture with no top or bottom enclosure is an example of a Maintenance Category I fixture. A direct-indirect fixture is a Category II; an industrial strip fixture with an apertured top and bottom is a Category III. Deep-celled parabolic fluorescent fixtures are Category IV fixtures. A lensed fluorescent troffer is a Maintenance Category V fixture. A pure indirect fixture is a Category VI. See the IESNA Lighting Handbook for evaluating dirt conditions.

Adding It All Up

Once all light loss factors are determined, multiply one against the next (A x B x C …) until a final Light Loss Factor (LLF) results that can be used in lighting design calculations.

Light Guide:
Controlling Glare

Luminance (Photometric Brightness)

The light that we actually see, brightness can be measured as the light leaving a lamp, or the light reflecting from an object's surface. It is measured in footlamberts (English) or candelas/square meter (metric).

Brightness can be used for a variety of purposes, from producing a sense of drama to creating sparkle and glitter elements in a space. The brighter a task is, the easier it is to see and the lower the amount of light that is required. Too little brightness decreases contrast and calls for a higher light level. But if not properly controlled, high brightness can produce levels of glare that either impair or prevent a desired task being performed. Glare can be described as direct or reflected glare, which can then result in discomfort or disability.

Direct glare comes straight from the light source. Reflected glare shows up on the task itself, such as a computer screen. Discomfort glare does not prevent seeing makes it uncomfortable. Disability glare prevents vision--a popular example is holding a glossy magazine at a certain angle; a veiling reflection results, impairing our reading of the page.

Strategies for Reducing Unwanted Glare

Strategies commonly employed to reduce unwanted levels of glare include:

Indirect lighting that throws more light upward than downward, diffusing the light and reducing glare on computer screens
Parabolic louvers, special lenses or other diffusing media on fixtures that diffuse the fixture's light output
In an office, it may be possible to de-emphasize the ambient lighting system with reduced light output and diffusing media, while providing adjustable task fixtures at workstations
Relocating the light source
Relocating the task or changing its orientation until the glare is removed
Changing the surface reflectance of the task
Use blinds or shades on windows to control the amount or transmittance angle of sunlight entering the space

Visual Comfort Probability

Visual comfort probability (VCP) is a rating on a scale of 0-100 given to indoor fixtures (in a uniform system with identical fixtures) to indicate how well accepted they are likely to be by the area's occupants. A VCP rating of 75, for example, indicates that 75% of the occupants in the poorest location would not be bothered by direct glare. Generally, office environments require that fixtures have a VCP rating of 70 or more, although this figure has been revised by some in recent years to 80 or more for environments where visual-task computers are used. The VCP rating for a given fixture can be found in its photometric test report. Generally, again, the higher the VCP rating, the lower the fixture's efficiency at transmitting light to the task.

Shielding Media Characteristics for Fluorescent 2x4 Recessed Troffer Fixtures:

Shielding Medium	Fixture Efficiency	VCP Rating

Clear Prismatic Lens	60-75%	50-70
Low-Glare Clear Lens	60-75%	75-85
Deep-Cell Parabolic Louver	50-70%	75-95
Translucent Diffuser	40-60%	40-50
Small-Cell Parabolic Louver	35-45%	99

Brightness Ratios

Brightness ratios in a space can affect how it is perceived. While high ratios of bright to dark in the space can produce contrast or a sense of drama, it can also be visually fatiguing during transient adaptation, which describes the eye adapting to changes in brightness. This can reduce productivity and can even be hazardous. The right approach is determined by the application; the IESNA has recommended brightness ratios for a wide range of environments.

Uniformity

Uniform light and brightness levels across a space can be desirable but may also be boring; in such cases, sparkle elements, color and/or other methods can be employed to create visual interest without causing fatigue.

Light Guide:
Lighting Audits

The first step to a successful lighting upgrade is the lighting survey or audit. In this stage, which is essential to proper planning, the lighting manager gathers and organizes information about the existing lighting system and how it is used.

Various software can serve as a valuable aid in collecting data. One such free resource is the ProjectKalc program from the U.S. Environmental Protection Agency's Green Lights Program.

Collect Financial Information

To conduct a full financial analysis that will be needed to justify an investment in upgrading the existing lighting system, gather data about the local utility rate structure and average charges for energy (kWh) and demand (kW).

Determine the availability of rebates from the local utility that may subsidize purchases of energy-efficient lighting equipment; also determine sources of financing and create assumptions for tax rates and inflation rates for materials and labor.

Collect General Information

Collect floorplans or reflected ceiling plans for the facility that show fixture locations and room dimensions (length in feet, width in feet, ceiling heights in feet and areas in square feet). Be sensitive that renovation work may have been performed over the years that has changed the original floorplans and/or reflected ceiling plans. If not available, create using graph paper.

Label each area (rooms, hallways, etc.) with a letter for future identification with sets of data that will be collected. Also label each area with a generic description (private office #2, lavatory #1, etc.). It may be desirable to put a sticker on each door hinge during the room-by-room survey that bears its identity that corresponds with the floorplan.

Also, gather as much information as possible about the building and its history; try to determine what future plans there are if any for the building.

Collect Occupant Information

A good way to learn about how occupants feel about their lighting system is with a survey, which can asks questions such as, "Do you have trouble with light reflecting off your computer screen?" An additional benefit of doing this is that it may help create "buy in" among building occupants for the new lighting system.

Should this path be taken, however, how caution in evaluating the answers; the occupants know little about lighting - - in fact, they rarely notice it unless something goes wrong. For example, an occupant saying there is too much light in an area probably is saying that it is too bright, which is an issue of glare, not quantity of footcandles.

Collect Lighting Information

For each area, identify:

Hours of operation
Type and size of fixtures
Number of fixtures (hand-held mechanical counters can help)
Number of lamps per fixture
Number of lamps per ballast
Type of lamps
Type of ballasts
Specular reflectors if already installed
Fixture condition
Whether fixtures are air-handlers, part of the air distribution system
Availability of daylight
Tasks that are performed in the space (with light level targets)
Use of partitions
Unique fixture types or physical features
Area dimensions
Height of the tasks
Fixture mounting height
Room surface reflectances and colors of major objects and room surfaces

Also determine lighting waste disposal regulations and costs.

Standardized forms can be created to help capture and organize information by area.

It may be desirable to plot existing light levels with a light meter, although this may result in misleading data because the condition of the fixture and point of life for the lamps may not be consistent from fixture to fixture. For this reason, it may be desirable to simply calculate existing light levels.

If the building is large, information can be extrapolated based on known data. For example, if the general lighting scheme is based on 2x4 fluorescent fixtures, and the spacing and room dimensions are known, an approximate number of fixtures can be extrapolated. Another method is to gather data for prototypical spaces, and then make assumptions for how other prototypical spaces are lighted (this method works best in large, homogenous spaces). However, when it comes to accuracy, of course, there is no substitute for a complete walkthrough.

It may be desirable to contact a lighting consultant to help conduct the walkthrough and survey.

Light Guide:
Lighting Upgrade Strategies

Upgrading a lighting system can reduce energy consumption in two ways. Since Energy = Power x Time, we can either reduce the lighting system's input wattage (W or kWh) or reduce its hours of operation. As the kW and the kWh are the basic products for which an electric utility charges, significant operating cost savings can result that can pay for the investment and then reduce a desirable return on that investment (see Retrofit Economics ).

It is beyond the scope of this article to discuss in detail every possible retrofit strategy. Readers are encouraged to see Lighting Upgrades by Damon Wood (The Fairmont Press, Inc.). For lighting retrofit fundamentals and retrofit management, the reader may be interested in seeing The Lighting Management Handbook (The Fairmont Press, Inc.) by the author. In this article, we will review general approaches to retrofitting.

Common Upgrade Strategies:

Upgrade with reduction in light levels

In some applications, ambient light levels can be reduced, particularly in spaces where ambient light is needed only for the task of orientation, in spaces where planned lighting maintenance is resulting in a light level higher than originally planned for, and in spaces where IES light level recommendations have been revised (that is, reduced).

Approaches include dimming, lamp/ballast removal, specular reflectors, reduced-output (lower-wattage lamps) and current limiters.

Increase light levels

This entails increasing light levels via planned lighting maintenance, specular reflectors, higher room surface reflectances or higher-output lamps and other approaches; after light levels are increased, we are then afforded the options to then reduce light level and save energy as shown under "upgrade with reduction in light levels."

Maintain light levels

In these spaces, we need to maintain current light levels but can do so by retrofitting with lighting equipment, such as more-efficient lamps and ballasts, to provide comparable light output at a reduced wattage.

Focus light levels

In some applications, the overhead ambient lighting system is doing most of the work in the space, providing illumination for both ambient and task lighting. In many of these applications, by providing portable, adjustable task fixtures at the task locations, we can upgrade to reduce light levels in the ambient system, since its primary function will be retasked for orientation only. An example of this approach is an indirect lighting scheme for ambient illumination, with task fixtures.

Reduce hours of use

Controls such as energy management systems, occupancy sensors and daylight-dimming ballasts can be installed to control the hours the lighting system is used, eliminating waste and reducing energy usage.

Before Beginning

Here are some useful guidelines to remember when attempting a lighting upgrade:

The lighting system must serve the design goals of the space; no upgrade should compromise the system's performance in meeting these goals. The upgrade should begin with the question, "What is the spaced used for and how does the lighting support that?"
There is no magic to new energy-efficient lighting systems; since all lighting equipment operates according to the laws of physics, there are always tradeoffs
All lighting components must be compatible to operate properly
All OSHA safety requirements should be met when any work is done on the lighting system
Ensure that all retrofits are permanent and understood by the maintenance personnel in a written and communicated lighting policy, so that old components are not reintroduced back into the lighting system later (such as when a screw-in compact fluorescent lamp fails and is then replaced with an incandescent lamp)
Planned lighting maintenance can be an effective means of getting the best results from the lighting system and can help create energy management opportunities
Be sure to include provisions for legal compliance in disposing of any lighting waste (see Lighting Waste Disposal)

Typical Fluorescent Fixture Upgrades

T8 Lamp/Ballast System
Specular Reflectors/Delamping
Current Limiters
Daylight-dimming Systems
T5 Twin-Tube Lamp/Ballast System
T10 Lamps
32W Heater Cut-out and 34W Energy-Saving T12 Lamps
25W T12 Lamps/T8 Ballasts
Premium Magnetic, Cathode Cut-out (Hybrid), Electronic Ballasts (Full Output, Dimmable, Light-Level Switching and Low-Wattage)
Lens/Louver Upgrades
Indirect Lighting w/Task Lighting
Task Lighting w/Reduced Ambient Lighting
New Fixtures

Compact Lighting Upgrades

Compact Fluorescent Lamps
Halogen Lamps
Krypton Incandescent Lamps
Electrodeless Downlight Lamps
Compact HID Lamps
New Fixtures

High-Intensity Discharge (HID) Lighting Upgrades

Energy-Saving Metal Halide and High Pressure Sodium (HPS) Lamps
Switching to Metal Halide or HPS Systems
HID Fixture Reflectors
High-Bay Compact Fluorescent Lamps
Dimming Ballasts
New Fixtures

Typical Exit Sign Upgrades

Compact Fluorescent Lamps
Low-Wattage Incandescent Lamps
LEDs
Electroluminescent Panels
New Exit Signs

Typical Control Upgrades

Lighting Management Systems
Dimmable Fluorescent And HID Ballasts
Daylight- and Lumen Maintenance-Dimming Systems
Electronic Timeclocks
Occupancy Sensors (many options available)
Manual, Step-Level And Panel-Level Dimming Systems
Current Limiters
Capacitive-Switching HID Systems

Light Guide:
Lighting & HVAC Interactions

Lighting systems convert only a minority fraction of their electrical input into useful light output. Much of the rest is released directly as heat into the space. Therefore, any upgrade of the lighting system that reduces input wattage reduces the amount of heat that must be removed by the air cooling system. This results in air cooling energy savings during the operation of the building. In new construction, an energy-efficient lighting design can result in significant savings in the installed cost of cooling systems.

A rule of thumb in the industry is that 1 kWh of air conditioning energy is saved for every 3 kWh of lighting energy. This, however, is often not accurate because it does not account for different climates. A retrofit in a building in Alaska, obviously, will not yield the same air conditioning energy savings benefit as in a building in Florida - in fact, in Alaska this heat is quite useful, and the retrofit could result in a much higher heating bill!

In the northern regions, the cost of additional heating can cancel out the air cooling energy savings, but in many areas of the United States the air cooling savings, which will be 0-30% of the lighting energy savings, will exceed this additional heating cost.

How to Calculate Air Cooling Energy Savings

Robert Rundquist, PE is the president of R.A. Rundquist Associates of Northampton, MA and a professional engineer with nearly three decades' experience in heating, ventilation and air conditioning (HVAC) system design, energy analysis and energy calculation research. He offers a formula to assess a more accurate figure for air cooling energy savings that was derived from both independent research and research conducted for the American Society of Heating, Refrigeration and Air Conditioning Engineers (ASHRAE). It has been validated by DOE-2 computer runs and other methods.

1. Lighting energy consumption must be reduced by a specific amount that stays constant throughout the year. This is most predictable in a retrofit, but can also work for some controls and other applications where hours of operation are reduced.

2. Determine the fraction of the year of the cooling season. (Download The Advanced Lighting Guidelines to get typical cooling seasons in the US)

3. Determine the fraction of the daily load met by mechanical cooling. Basically, this question asks, how much of the lighting system's heat must be removed by the cooling system? Usually this is about 90%, with 10% dissipated.

4. Determine the air cooling system's coefficient of performance. Tests on cooling systems have shown that for every watt (W or kW) put into the system, 2.7 watts (W or kW) of cool air is produced. The actual figure can vary, however, due to a range of factors; the 2.7 figure can be used although it is best to use the actual system's coefficient of performance.

5. Calculate using the formula below:

Fraction of Lighting Savings as Air Cooling Savings =

Fraction of the Year of the Cooling Season

x Lighting Load Met by Mechanical Cooling

÷ System's Coefficient of Performance

6. Example: Suppose we retrofit a system in Raleigh, North Carolina, which has a cooling season of 30 weeks, and remove 20,000kWh from the lighting load.

Fraction of Lighting Savings as Air Cooling Savings =

30 ÷ 52 = 0.5769 or 0.58

x 0.9

÷ 2.7

= 0.19

That means that for every 1 kWh of lighting saved, we save 0.19 kWh of air cooling energy. In our example, this means that we have removed 3,800kWh (20,000kWh x 0.19) of air cooling load. If the local utility charges an average commercial rate of $0.065 per kWh, then we have reduced energy costs by $1,300 per year for lighting and an additional $247 per year for air cooling.

Light Guide:
Lighting Waste Disposal

Both lighting upgrades and routine maintenance entail the removal of lamps and ballasts from the system. These lamps and ballasts must be disposed of according to state and Federal regulations; if they conflict, then the stricter regulations must be obeyed. Mercury-containing fluorescent and high-intensity discharge (HID) lamps and PCB-containing ballasts are two types of potentially hazardous waste.

Lamps

All fluorescent and HID lamps have mercury content. The U.S. Environmental Protection Agency (EPA) regulates mercury disposal under the Resource Conservation and Recovery Act (RCRA). Because the cost of testing the lamps may be prohibitive, it is generally wise to consider all lamps being disposed of as hazardous waste. As hazardous waste, lamps must either be recycled or disposed of in hazardous waste landfills as opposed to municipal solid waste landfills. They cannot be incinerated.

Small generators are exempt from RCRA regulations. Small generators are companies that generate less than 100 kilograms of hazardous waste per month; in terms of lamps only, this is about 300-350 4 ft. T12 lamps or 400-450 4 ft. T8 lamps per month.

The cost of recycling a 4 ft. fluorescent lamp can be about $0.50-0.75/lamp vs. about $0.25-$0.50 for landfill disposal (as of 1995, source: EPA Green Lights); usually, recycling does not make the initial cost of a lighting upgrade unprofitable. When fluorescent lamps are recycled, the waste is crushed, then separated into phosphor powder, recovered mercury, metal and glass that are eventually put to reuse.

In recent years, the major lamp manufacturers have introduced a number of low-mercury fluorescent and HID lamps (example: Philips' Alto fluorescent lamp) that are designed to pass EPA tests, allowing them to be disposed of in municipal solid waste landfills. Check with the state hazardous waste agency or agencies having jurisdiction to see if the lamps can be disposed of as solid waste.

In addition, both the U.S. EPA and the states have been relaxing their regulations regarding the disposal of fluorescent and HID lamps. Again, check with the applicable state hazardous waste agency or agencies to determine the specific requirements for handling, storage, transportation and disposal of mercury-containing lamps.

Also, for more information, contact the EPA's Hazardous Waste Hotline at (800) 424-9346.

Ballasts

Ballasts manufactured and distributed in the United States prior to 1979 contain polychlorinated biphenyls (PCBs), which is a hazardous material. Since many magnetic ballasts can enjoy a service life of 25 years or longer, many of these ballasts are still in existence. If a ballast label is marked "NO PCBs," then it is not a PCB ballast; if there is no such marking, then the ballast is assumed to contain PCB fluid. Handling and disposal instructions for ballasts with PCBs can be found on this EPA web page: www.epa.gov/pcb/guidance.html

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	A 10’ flat is painted to represent what will be used in the scenery. Samples of fabric, large enough to have folds and dimension, are attached to the appropriate sections of the flat This will help determine what a pink dress might look like used against blue scenery.
Colored light is added by simply shining a small theatrical fixture that is equipped with the Roscolux colors to be used in the production. This technique isn’t perfect, of course, but it is the best method we know to predict, in advance, what the effect will be when the scenic paint, costumes and light are combined on stage.