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the last 40 years, much advancement has been made in the area of lighting technology. Workspacesof the 1960s and ’70s were designed around the belief that more light leads to better visual per-

formance. Thus, they typically provided more light than the job required with little or no flexibility for the user. The result was wasted energy and a variety of human-factors issues, such as eyestrain andheadaches. New scientific research and enhanced technologies have provided designers with smartersolutions. Unfortunately, many offices continue to use dated technology to illuminate workspaces.Today’s workplace calls for flexible lighting systems that support the tools of the modern office, such asmonitors and notebook computers. This suggests the integration of more appropriate lighting solutionsinto existing lighting plans, and the selection of the most advanced products for new-build situations.

“The more we come to understand about lighting the more we appreciate its importance. Lightingprojects present a significant opportunity for us to add value to our facilities and improve the workplace,”says James Woods, Energy Conservation Officer for the U.S. Department of Commerce.

Office lighting design continues to move toward greater energy efficiency, while providingimprovements for worker comfort and safety. This move toward environmentally responsible design canbe further developed with the incorporation of task lighting into workplace lighting schemes that wouldtypically use just ambient or overhead light sources.

Recent research into the use of task lighting has provided evidence that incorporating positionablelight sources into individual workspaces provides many benefits with regard to energy consumption.Additionally, it provides individual workers the freedom to position their light sources most comfortably.

“At the Department of State we’ve learned from experience that our employees feel stronglyabout having good lighting, and that user-controlled lighting can help our people accomplish theirmissions. Energy and cost savings along with improved environments give us the best of both worlds,”

CONTINUING EDUCATIONUse the learning objectives below to focus

your study as you read Bright Ideas—Office

Lighting 101. To earn one AIA/CES Learning

Unit, including one hour of health safety welfare credit,

answer the questions on page 192f, then follow the

reporting instructions on page 230 or go to the Contin-

uing Education section on archrecord.construction.com

and follow the reporting instructions.

LEARNING OBJECTIVESAfter reading this article, you should be able to:

• More effectively evaluate office lighting design

• Understand the importance of incorporating task lighting

into an overall lighting plan

• Identify the environmental and worker health-related

benefits of certain types of task lighting

AIA/ARCHITECTURAL RECORDCONTINUING EDUCATION Series

Bright Ideas—Office Lighting 101.

HUMANSCALE PRESENTS Bright Ideas—Office Lighting 101With recent improvements in lighting technology and a better understanding of lightingissues, you can have the best of both worlds—reduced lighting costs and increasedworker comfort and performance.

In

Architectural Record Version: 01Issue Date: September 2004Page No: 192a

Filename: 09/04Humanscale(reprint).qxdWriter /Designer: Kenneth KaiserLast Revision: xx

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says Richard Tim Arthurs, Energy Policy and Conservation Officer, Office ofFacilities Management Services, U.S. State Department.

In the 1970s, when it came to lighting our workspace, more was better.Recent research has shown us that more is not better, and in fact not desired by most workers. Providing too much light can lead to the following:• Energy waste• Emotional and physical discomfort for the office worker due to improper

illumination of the work surface and glare on reflective surfaces (such as the computer monitor)

Using positionable task lighting in addition to low ambient light can lead to the following:• Improved lighting quality, comfort and control for workers• Increased energy efficiency

Task lighting can provide illumination where it is most needed — onpaper-based documents — more economically than the most energy-efficientceiling ambient light because task lighting is located closer to what’s being lit.In addition, individual workers can gain control over their lighting as appropriatefor the task being completed.

The monitor—document conflict“The demands of differing tasks within the workplace create an obvious conflictin lighting requirements,” says researcher Alan Hedge, PhD, CPE, Director of theHuman Factors and Ergonomics Laboratory at the Cornell University Depart-ment of Design and Environmental Analysis.

The majority of work that most office workers perform today is a combina-tion of viewing a monitor and reading documents or other printed material.Yet these two tasks require significantly different levels of light.

If the ambient lighting level is set at the appropriate level for reading printeddocuments (20–50 footcandles), the lighting intensity will be much too high forproper monitor viewing (5–10 footcandles required). This leads to glare on thesurface of the monitor, substantial energy waste and a variety of worker produc-tivity issues. However, if the ambient lighting level is brought down to a pointwhich is appropriate for monitor viewing and movement throughout the work-space, then there won’t be nearly enough light to read documents and otherpaper-based reading material.

The solution to this conflict is to lower the overall ambient lighting levels andprovide individuals with positionable task lights to properly illuminate the read-ing material on the desktop. In this way, both the monitor and documents canbe lit to appropriate levels for the tasks being performed.

Bulb options and energy efficiencyToday’s task lights utilize one of three primary bulb types: incandescent, halogen orcompact fluorescent. Compact fluorescents burn cooler and have proven to bemore efficient than any other available task light source. A regular incandescent orhalogen bulb works by heating a metal wire to a temperature at which it glows.This requires high temperatures, relatively large amounts of energy, and creates ahot bulb surface. In fact, halogen bulbs can reach temperatures of 1800º and havetherefore been banned from many university dormitories because of their risk as afire hazard. A compact fluorescent bulb is a low-pressure mercury, electric-dis-charge lamp in which phosphor coating transforms ultraviolet energy, created byelectric discharge, into visible light. The fluorescent bulb remains much cooler anduses less energy than the other two, while providing the same amount of light.

The first practical electric lamp, developed by Thomas Edison in 1879, convertedless than one percent of electricity into light. Today’s household incandescent bulbsconvert 6–7 percent of their electrical input into light. The rest is wasted as heat. Clas-sic 4-ft fluorescent systems convert approximately 19% of their energy into light.

Today’s compact fluorescent lamps, five inches in length, or less, can be 50 timesmore efficient than Edison’s original lamp and eight times more efficient than anincandescent light source capable of the same light output. For example, a 13-wattcompact fluorescent task light will produce the same light output as a 75-wattincandescent light, burn cooler and consume only one-quarter of the electricity.

As we age, we need more light to readThe older we get, the more light we need to see. Research indicates that the visualperformance of those in their 20s is about eight times better than those in their60s, almost four times better than those in their 50s. Those 61 and older requiremore than 350 percent more contrast than do those in their 20s.

As we age, our eyes undergo several physiological changes—including the development of opacities in our lens and a reduction in pupil size—that result in our need for more light.

400

350

300

250

200

150

100

50

020-30 31-40 41-50 51-60 61-70

Relative Contrast Required as a Function of Age

Rela

tive

Con

tras

t Re

quir

ed

Age

Incandescent Bulb 100W

Halogen Bulb100W

Compact Fluorescent 26W

LUMENS PRODUCED

LIGHT QUALITY

CRI (COLOR RENDERING INDEX)

ENERGY CONSUMPTION

BULB TEMPERATURE

BULB LIFE

COST OF BULB

BULB LIFE (ON AVERAGE)

BULBS NECESSARY

ANNUAL ENERGY COST

TOTAL COST

1690

White/Yellowish

>90

100 W

500° F

1000 hrs

$0.50

167 Days

10

$21.90

$103.55

1900

Very bright,white light

>98

100 W(or more due to heat)

1800°F

2500 hrs

$4.00

416 Days

4

$21.90

$114.55

1825

Available fromwarm to crisp/cool

>84

26 W

125° F

10000 hrs

$14.00

1642.5 Days (4.5 Years)

1

$5.91

$40.6o

Light Bulb Comparison Chart

(OVER 4.5 YEARS)

(OVER 4.5 YEARS)

* Assuming 6 hours of usage per day at $0.10 per kilowatt-hour Source: U.S. Department of Energy




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This increased need for light is due to a number of physiological changes inour visual system that occur as we age.

The term presbyopia means “old eye” and is a vision condition involvingthe loss of the eye’s ability to focus on close objects. Presbyopia, also referred toas farsightedness, occurs gradually over a number of years. Symptoms are usu-ally noticeable by age 45 and continue to develop until the process stabilizessome 10–20 years later.

In the eye, the crystalline lens is located just behind the iris and the pupil. Tinyciliary muscles push and pull the lens, adjusting its curvature, and thereby adjustingthe eye’s focal power to bring objects into focus. As individuals age, the lens devel-ops opacities and becomes less flexible and elastic, making accommodation moredifficult. Because these changes result in inadequate adjust-ment of the lens of the eye for various distances, objectsthat are close will appear blurry.

The muscles which control the diameter of thepupil also deteriorate with age. This reduces the size ofthe pupil, and limits the range and speed with whichthe pupil can adjust to varying light levels. This, com-bined with the increased opacity of the crystalline lens,increases the amount of light necessary to achieve thesame level of retinal illumination.

Eyestrain and accompanying headaches, which canresult from working under inadequate illumination, areaggravated by aging. Eye fatigue may result in blurryvision and dim lighting aggravates the problem. Tasklighting allows us to achieve the correct levels of illumi-nation, regardless of the task or vision requirements, bychanging the distance between the light source and thelit object—closer for more light, further away for less.It also allows us to correctly position the angle of lightto eliminate glare and veiling reflections.

Task lighting saves eyes and energyTask lights, because they are closer to the work surface,are a considerably more effective means of lighting adesktop than are overhead fixtures. A task light using a26-watt compact fluorescent lamp will consume far lessenergy to illuminate a work area than will a typicaloverhead lighting fixture. A work environment canmaintain lower levels of overhead lighting by illuminating

desktops with energy-efficient task lights. In addition, maintenance and bulbreplacement costs are less with task lighting. Research suggests that with theuse of energy efficient lighting technologies, we can reduce overall electricaluse for lighting by half, a move that would save over $20 billion annually anddecrease powerplant emissions by millions of tons.

According to the California Energy Commission, lighting accounts for 23percent of the electricity used in the state. The actual figure may be consider-ably higher, say other sources. Five percent of electricity used for air condition-ing, for example, goes to eliminate heat generated by lighting. In general, how-ever, the EPA estimates that lighting accounts for 20–25 percent of the electric-ity used annually in the United States.

Since the 1970s, huge strides have been made in office lighting efficiency.Still, say California officials, the potential exists to reduce lighting energy useand peak demand by an additional 50 percent by 2020 while still improving the quality of lighting to the end user.

Research by the U.S. Environmental Protection Agency has found thatlighting for industry, offices, stores and warehouses represents from 80–90percent of the total lighting electricity use in the United States. The Institutefor Research in Construction, an arm of the National Research Council Canada,has found that if energy-efficient lighting were used everywhere it was profitable,the electricity required for lighting would be cut by 50 percent, and aggregatenational electricity demand would be reduced by 10 percent. This reduction in demand would significantly reduce power plant emissions, pollutants,and wastes, say federal researchers.

Flux, illuminance and luminanceTotal flux, in lumens, is the parameter that bulb manufacturers use whendescribing the total amount of light given off by a bulb in all directions.Lumens do not, however, tell us how much light will be received where it isneeded. Illuminance, on the other hand, tells us how much light will reach agiven surface. Illuminance is generally measured in lux: a short form forlumens per square meter of surface area, the metric equivalent of footcan-dles (which represent lumens per square foot). There are 10.76 lux in onefootcandle, but the lighting industry typically rounds this factor off to 10.0for the sake of simplicity.



Lowered ambient lighting levels for proper monitor viewing combined with task lights for proper document illumination providethe right amount of light for different tasks while saving money and improving worker comfort, productivity and job satisfaction.

Despite being considered “task lights”, under-the-bin lighting solutions are a major source of glareand are not an adequate alternative to positional task lighting.

Thirty years ago, standards of the Illuminating Engineers Society ofNorth America (IES) called for general office lighting in the range of 100–150footcandles (1,000–1,500 lux). Huge, increasingly cubicled floorplates, oftenwithout any natural, outside illumination, were lighted, for the most part, bybanks of 4-ft , ceiling-mounted fluorescent troffers (recessed fluorescent fix-tures) that, in too many cases, resembled stadium floodlights in their intensity.

By 2002, nearly all office tasks were being performed on desktop com-puters and average ambient light levels in the American workplace declinedto one-third of 1970s levels. Today, ambient office lighting is likely to be inthe range of 25–45 footcandles (250–450 lux), which is still far more lightthan is necessary for getting around the office or viewing a computerscreen. According to IES, computers are best viewed in an environmentwhere the ambient lighting is 5–10 footcandles (50–100 lux), whereas mostreading requires 20–50 footcandles (200–500 lux).

Luminance, in candela per square meter (cd/m2 is a measure of how brightan object appears (1 cd/m2=0.29 foot-lamberts, the imperial unit for lumi-nance). Luminance is a representation of the amount of light seen by the eye.Luminance is sometimes specified for critical lighting designs (e.g., IES Recom-mended Practice RP-24 for Offices with Video Display Terminals).However, illuminance is usually the parameter of preference because it is indirectlyrelated to what the eye sees. Knowing the reflectance properties of illuminatedsurfaces, it is possible to calculate luminance from illuminance using proceduresin the IES Lighting Handbook. IES lighting recommendations are usually givenin terms of illuminance because it is more practical to measure.

If we compare a lighting fixture to a shower head, then the lumen output, ortotal flux, is the rate of flow of water and illuminance is the amount of watercollected in a bucket at a given time. The key point is that the same total fluxcan give different amounts of water in the bucket, simply by moving the bucket,or by changing the spray pattern or by changing any physical obstructionsbetween the source and the bucket. Total flux doesn’t specify how much illumi-nance will be provided where it’s needed. This is true, in part, because the lumi-naire, reflectors, lenses and other optical media can greatly affect the flow oflight from the source to the work surface. Failure to remember this is a frequentcause of poor lighting design, especially in retrofit applications.

For lighting designs, we should not assume that two lamps with the samelumen rating will each give the same amount of light where needed.






Dated lighting schemes based solely on overhead fixtures provide an incomplete and inefficientlighting solution that wastes energy and has both physical and performance implications for workers.

ACTIVITY CATEGORY LUX FOOTCANDLES

s Indicates typical office task

---------------------------------------------------------------------------------------------------------------------Public spaces with A 20-30-50 2-3-5 dark surroundings---------------------------------------------------------------------------------------------------------------------Simple orientation for short B 50-75-100 5-7.5-10temporary visits

s View CRT screen

---------------------------------------------------------------------------------------------------------------------Working spaces where visual tasks C 100-150-200 10-15-20are only occasionally performed---------------------------------------------------------------------------------------------------------------------Performance of visual tasks of D 200-300-500 20-30-50high contrast or large size

s Read standard document, photocopy or newspaper

---------------------------------------------------------------------------------------------------------------------Performance of visual tasks of E 500-750-1000 50-75-100medium contrast or small size

s View photo in moderate detail; reference phone book

---------------------------------------------------------------------------------------------------------------------Performance of visual tasks of F 1000-1500-2000 100-150-200low contrast or very small size---------------------------------------------------------------------------------------------------------------------Performance of visual tasks of G 2000-3000-5000 200-300-500low contrast or very small sizeover a prolonged period---------------------------------------------------------------------------------------------------------------------Performance of very prolonged H 5000-7500-10000 500-750-1000and exacting visual tasks ---------------------------------------------------------------------------------------------------------------------Performance of very special I 10000-15000-20000 1000-1500-2000visual tasks of extremely low contrast---------------------------------------------------------------------------------------------------------------------A-C for illuminances over a large area (i.e. lobby space) D-F for localized tasks G-I for extremely difficult visual tasks

IES Illumination Categories & Recommended Values






Rough estimations of illuminance can be made by dividing the candelas by thesquare of the distance between the light source and the surface illuminated. Forexample, if a fixture gives 2000 candelas in the downwards direction, and if wemount that fixture in a 10-ft high ceiling, then the illuminance from that fixture willbe approximately 2000/102=20 footcandles at the floor directly below the fixture.In metric units, one would calculate 2000/(3.048m)2=215 lux. Calculations of thistype work as long as the distance to the surface is at least four times greater than themaximum dimensions (i.e., length or width) of the light source. For shorter dis-tances, the calculations may still be used but they are subject to a greater uncertainty.

Ballast technologyAll fluorescent lamps require ballasts, which stabilize and control the electricalcurrent that gets sent to the lamp. These ballasts are available in two primarytypes: magnetic and electronic.

Magnetic ballasts use long-standing technology, and with few compo-nents susceptible to failure, they are likely to last for 20 years or more, farlonger than most electronic ballasts. However, electronic ballasts have theedge in performance and health considerations. Electronic ballasts aremore energy efficient than magnetic ballasts because they operate lamps athigher frequencies (above 20,000 Hz versus 60 Hz for magnetic ballasts).

High-frequency operation also reduces perceptible flicker. The health ben-efits seen with electronic ballasts are attributable to the reduction in flick-er as visual demands are reduced.

Electronic ballasts can increase the efficiency of fluorescent lighting systemsby as much as 29 percent over systems using magnetic ballasts, while at thesame time extending bulb life.

Electronic ballasts are either instant start or rapid start. Instant start ballasts,which produce a high starting voltage which is then quickly reduced, are moreenergy efficient. Rapid start ballasts heat the lamp cathodes before triggeringillumination, helping to maximize the life of the ballast and the bulb.

Among the findings of National Research Council Canada researchers GuyNewsham and Jennifer Veitch, designs utilizing electronic ballasts:

• resulted in workers typing 21 percent faster during creative writing exercises

• improved workers’ reaction times by eight percent

• lowered incidence of headaches and eyestrain

“Our findings provide good news for the lighting community,” they conclude.

“The goals of improving energy efficiency and lighting quality are compatible.

People who worked under electronic ballasts…showed better visual performance,

did better on reading and writing tasks and rated the tasks less difficult.”

For Detroit-based Smith Group, Inc., an A/E firmwith its own in-house lighting group, the goal of asoon-to-be-completed, nine-building campus inVan Buren Township, Michigan, for auto parts sup-plier, Visteon, was “the absolute minimization” ofenergy costs, says James Luckey, AIA, SeniorDesign Architect.

The first consideration was natural light. Toallow as much light as possible into interiors, Luck-ey designed all of the 100,000–150,000-sq-ft build-ings to be “extremely narrow,” 64 feet in width. “Wewanted this project to conform to the Europeanstandard, in which workers are never more than 10meters from a window,” he says.

Exposures are large: sills of 15-ft-wide windowsare only 2-ft off floors; headers are 10-ft above floorheight; ceilings at 11ft 6 in. “We like, whenever pos-sible, to push ceiling height,” says Luckey.

Ambient lighting, via direct-indirect pendants(75 percent upward, 25 percent downward), cen-tered in 20-ft ceiling bays, 30 inches beneath ceil-ings, is at 30 footcandles and is automated. “Mostdays, in all likelihood,” Lucky figures, “ambientlighting will not be turned on.”

For “sparkle,” Smith used café and track lights.Each 50-sq-ft workstation will also have at least onecompact fluorescent task light capable of providing50–75 footcandles where it is needed.

“The use of task lighting allows higher intensi-ties only where that level of light is needed,” saysLuckey. “In a computer environment, the goal is tominimize light pollution. This project, he says, is inkeeping with what we try to do with every project.If ceilings are shallower, we have no choice but toput lights in the ceiling plane, but we prefer not to.”

At Visteon’s new corporate campus, which willopen incrementally from August through Decem-ber, workers not only will control lighting withinindividual workstations, but individual controls willallow them to control floor-distributed heating andcooling as well.

Overall lighting consumption, Luckey says,is one watt per sq ft; lighting and miscellaneouspower consumption, 2.25 watts per sq ft — the

figure excludes air-handling.“Perhaps more importantly,” Luckey says,

“ASHRAE 90.1 sets a standard of 94,842 BTUs(British thermal units) per square foot per year. Vis-teon Village will consume about 59,000 BTUs persquare foot per year—a 37 percent energy reduc-tion from the code allowance. That number includesunder-floor heating and cooling consumption.”

“When it comes to lighting, there is a lot moreto think about than most people realize,” saysDenise B. Fong, IALD, LC, LEED, a principal atSeattle-based Candela Architectural Lighting Con-sultants.

It is not enough to rely upon standards, Fongsays. “One of the things we do because the energycode tells us to do it, is to calculate consumption bywatts per square foot, but that tells us little aboutthe ‘quality’ of light.”

“We don’t see, for instance, what the light metermeasures,” says Fong. “We see reflected light. If youwere to meter light in a room painted half blackand half white, a light meter will give you the samereading in either space, but to our eyes, the areawith black surfaces will appear darker because thereis less reflection.”

She suggests a growing interest in the use of tasklighting, mentioning, “Task lighting is not some-thing we lighting designers pay much attention to,but there are cost benefits associated with tasklighting. In general, the use of task lighting enablesyou to reduce the general ambient light level.”

“There are still a lot of projects out there whereall the lighting is in the ceiling, but energy codes areforcing us to rethink that strategy,” Fong says.

According to an assessment by the LightingResearch Center at RPI, more than one-third of allU.S. workers occupy partitioned workstations, andunder-shelf task lighting accounts for 90 percent ofall task lighting sold.

“If partitions are shelved, and if the task light isbeneath the shelf,” Fong says, “light is not whereyou need it, and glare is almost always a problem.”Glare happens when the light source, the objectbeing lit and the eyes are all in the same plane. In

the case of under-shelf lighting, the light originatesunder the shelf, hits the work surface and bouncesdirectly into the eyes of the worker.

The solution, Fong says, is an “asymmetric” tasklight that uses specially designed reflectors to con-centrate light in one direction. This allows the userto position the light off to the side so that thebeams of light are directed across the front of theuser, instead of toward them.

“If you are right-handed, an asymmetric tasklight located to the left of your work area will putthe highest light output in the middle of your worksurface, and the light will bounce away from you soyou don’t get any glare from the lamp,” she adds.

“The most common design error, clearly, is themismatch between where light is being deliveredand where people are utilizing that light,” says AlanHedge. “All too often we put light into a buildingwithout knowing the ultimate layout. Even if thelayout is known, things can happen that are notforeseen. Offices may be partitioned differently bynew tenants, for instance, and the new layout canresult in a feast or famine situation, so far as light isconcerned. Some workers may complain of glareand headaches; some may be in the dark.”

In a study conducted in 1990, Cornellresearchers drew on an American Society of Interi-or Designers survey in which 68 percent of employ-ees complained about the light in their offices and79 percent of VDT users wanted better lighting.The Cornell study came to the conclusion that eye-strain was the number one health hazard in theworkplace—ahead of radiation, asbestos, or expo-sure to AIDS.

Hedge says eyestrain remains the number onecomplaint in the office environment, and thedegree of dissatisfaction is difficult to ignore. Itconfirms the need to identify the best availablemethods of lighting.

How essential a component is task lighting increating an effective office lighting scheme? “It islikely to be the most effective solution in any envi-ronment in which workers are doing both paperwork and computer work,” says Hedge. n

SMITH GROUP: TASK LIGHTING ESSENTIAL






LEARNING OBJECTIVES• More effectively evaluate office lighting design

• Understand the importance of incorporating task lighting into an overall

lighting plan

• Identify the environmental and worker health-related benefits of certain

types of task lighting

INSTRUCTIONS Refer to the learning objectives above. Complete the questions below.

Go to the self-report form on page 230. Follow the reporting instruc-

tions, answer the test questions and submit the form. Or use the Contin-

uing Education self-report form on Record’s website — archrecord.con-

struction.com — to receive one AIA/CES Learning Unit including one

hour of health safety welfare credit.

QUESTIONS

1. Ambient light levels in the American workplace have declined to one-

third of 1970s levels. Today, ambient office lighting is likely to be in the

range of:

a. 25–45 footcandles.

b. 35–55 footcandles

c. 35–55 lux

d. 135–145 footcandles

2. Those 50 years of age and older require what percentage more contrast

than do those in their 20s?

a. 125 percent

b. 50 percent

c. 350 percent

d. 250 percent

3. A 13-watt compact fluorescent task light will produce the same light

output as a 75-watt incandescent light.

a. true

b. false

4. Lamps that are high to very high in color temperature (5,000k to

7,500k) provide improved visual acuity compared to lower-color

temperature lamps (typically 3,500k) at the same light level.

a. true

b. false

5. According to the California Energy Commission, lighting accounts for

what percentage of the electricity used in the state?

a. 7 percent

b. 13 percent

c. 23 percent

d. 35 percent

6. Today’s household incandescent bulbs convert what percentage of their

electrical input into light?

a. 6–7 percent

b. 3 percent

c. 19 percent

d. 28 percent

7. California officials say the potential exists to reduce lighting energy use

and peak demand in the state by up to what percentage by the year 2020?

a. 15 percent

b. 35 percent

c. 50 percent

d. 375 percent

8. If a fixture gives 2000 candelas in the downwards direction, and if we

mount that fixture in a 10-ft high ceiling, the illuminance from that

fixture will be how many footcandles at the floor directly below the fixture?

a. 20

b. 50

c. 100

d. 200

9. High-frequency electronic ballasts can increase the efficiency of

fluorescent lighting systems by what percentage over systems using

magnetic ballasts?

a. 9 percent

b. 14 percent

c. 29 percent

d. 83 percent

10. Which has the greater light output: a 26-watt fluorescent lamp or a 100-

watt incandescent lamp?

a. a 26-watt fluorescent

b. a 100-watt incandescent


CLICK FOR ADDITIONAL REQUIRED READINGThe article continues online at: archrecord.construction.com/resources/conteduc/archives/0409human-1.asp. To receive AIA/CES credit, you arerequired to read this additional text. For a faxed copy of the material, contact Humanscale Customer Service at (800) 400-0625 or via email [email protected]. The following quiz questions include information from this material.

The color of lightOne aspect of lighting that often gets overlooked is bulb color tempera-ture, which describes the color appearance of the bulb, not the objectbeing viewed. Color temperature ranges from 3000 Kelvin for “warm”sources like incandescent lamps, to approximately 6500 Kelvin for “cool”sources like daylight fluorescent. Color temperature data is readily avail-able from lamp manufacturers. The selection of color temperature shouldbe considered relative to the application.

Lamps that are high to very high in color temperature (5,000K to 7,500K)provide improved visual acuity compared to lower-color temperature lamps(typically 3,500K) at the same light level. Visual acuity is generally defined assharpness of vision, with normal visual acuity rated at 20/20. High color tem-perature lamps are rich in the blue portion of the color spectrum and have anoticeably “cool” appearance.

The Color Rendering Index, or CRI, of a bulb specifies on a scale of 1 to

100 how colored objects appear under that bulb’s light compared to theirappearance in daylight. A CRI of 100 means no difference, while a low CRIcould mean a big difference. Incandescent lamps typically have CRIs above 90,but that doesn’t mean that they always give suitable results. Suppose, for exam-ple, we wish to illuminate white cabinets in a kitchen or a hospital examinationroom. A design objective might be to enhance the impression of whiteness,cleanliness and sterility. In this case, the color temperature of incandescentswould be too low to achieve the desired effect. As a general rule, one shouldtherefore select color temperature first, then pick the lamp giving the optimumCRI for the application.

Most fluorescent lamps operate at 3,000K to 4,100K, with a CRI from thelow 50s to 86, but recent technology gains now give us fluorescents with CRIsabove 90. A “full-spectrum” lamp is generally defined as a lamp having a Color-Rendering Index (CRI) of 90 or above and a color temperature of 5,000 degreesKelvin or above. n






(800) 400-0625www.humanscale.com

What is task lighting and why should we use it?

Task lighting provides the correct amount of light for the task being per-

formed. Viewing a computer monitor or walking down the aisle requires

far less light than does reading a typewritten page, making it neither effec-

tive nor efficient to light the entire environment at the same level. When

utilizing task lighting, the general lighting level in the facility can be low-

ered to a level appropriate for monitor viewing, thus creating a softer,

more pleasant atmosphere and saving energy. Work surfaces are supple-

mented with task lighting to give workers total control over where and

how much light they need for other tasks, such as reading a document.

Why choose a compact fluorescent task light?

Compact fluorescent bulbs use less energy than incandescents (about one

fourth), output more light (approximately three times as much) and last

up to 10 times longer. Compact fluorescent bulbs are also much cooler in

operation than regular incandescent bulbs or halogen bulbs and are, there-

by, safer and more comfortable to work near.

How does a mini-fluorescent bulb differ from earlier generation fluores-

cents? As I understand it, mini-fluorescents were used in earlier genera-

tion task lights but fell out of favor when halogen bulbs were introduced.

First generation “mini” or “compact” fluorescent bulbs suffered from flick-

er, low light and an audible hum. These objectionable characteristics have

been eliminated in the current generation of mini-fluorescents and accom-

panying ballasts. Today’s fluorescents are long-lasting and have a light out-

put as good as, if not better than, halogen or regular incandescent bulbs.

What Color Rendering Index (CRI) should task light bulbs have?

CRI is a method for describing the effect of a light source on the color appear-

ance of objects being illuminated. A CRI of 100 represents the reference condi-

tion of daylight (and thus the maximum CRI possible). In general, low CRI

illumination may render some colors unnatural and lamps with a CRI under

60 should not be used. It has been proven that at a certain point, the higher the

CRI, the lower the illuminance. A CRI in the 80s is good for all general tasks.

I don’t like the light given off by fluorescent bulbs. Can they be made

to give off a warmer light like incandescents?

Yes, compact fluorescent bulbs are available in color temperatures ranging

from 2700K for warmer light to approximately 4100K for cooler sources like

daylight fluorescent.

I’ve heard that “full-spectrum lighting” is better than regular fluores-

cent lighting. Is that true?

The short answer is “no.” Any bulb with a CRI of over 90 is considered a full-

spectrum bulb. Full-spectrum lighting is neither better nor worse than any

other lamp type. Claims made for its beneficial effects go beyond what scientif-

ic literature will support.

What is the difference between a magnetic and electronic ballast?

Magnetic ballasts use coiled wire to create a magnetic field that transforms voltage.

A magnetic ballast does not change the frequency of the power to the lamp—it

remains the same as the input power, which in the U.S. is 60 Hz. Electronic ballasts

use solid-state components to transform voltage, while also changing the frequency

from 60 Hz to 20,000 Hz or higher, depending on the ballast. Because electronic

ballasts don’t use coils or electromagnetic fields, they can function more efficiently

and cooler than magnetic ballasts. However, they are also more prone to failure. n

FREQUENTLY ASKED QUESTIONS

Color Rendering Index (CRI): method for describing the effect of a light source on the color appearance of objects being illuminated. A CRI of 100 repre-sents the reference condition of daylight (and thus the maximum CRI possible). In general, low CRI illumination may render some colors unnatural.

Footcandle: unit of measurement indicating how much illumination reaches a surface, equal to one lumen striking an area of one square foot.

Ballast: a device used with an electric-discharge lamp to obtain the necessary circuit conditions (voltage, current and wave form) for starting and operating. Aballast can be electronic or magnetic.

Lumen: the unit of measurement used to describe the output from a light.

Lux: unit of illumination closely equivalent to 1/10 of one footcandle.

Two-Component Lighting: combination of indirect general (ambient) light and task lighting.

GLOSSARY

Humanscale designs and manufactures ergonomic products for a more comfortable workplace. From the Freedom chair to the Diffrient Light – each product isdesigned to improve the health, efficiency and quality of work life. Humanscale’s seating, monitor arms, lighting, keyboard supports and other ergonomicaccessories follow the belief that if a design solves a functional problem as simply and elegantly as possible, the resulting form will be honest and timeless.

Headquartered in New York City, with global distribution, Humanscale remains the leader in ergonomic design. For more information contact CustomerService at 800-400-0625; or visit the website at www.humanscale.com.

ABOUT HUMANSCALE

Architectural Record Version: 01Issue Date: xxPage No: xx





Reprinted with permission from Architectural Record, September 2004

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