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Type I
The type I distribution is ideal for narrow walkways or bike paths. It's intended to be located at or near the center of the pathway, approximately two mounting heights in width.
Type II
The type II distribution is ideal for wider walkways, entrance roadways, bike paths and other long and narrow lighting applications. Intended to be located near the side of a roadway, approximately 1.75 mounting heights in width.
Type III
The type III distribution is ideal for roadway, general parking, and other area lighting applications. Intended to be located near the side of the area, approximately 2.75 mounting heights in width.
Type IV
The type IV distribution is especially suited for wall mounting applications and for illuminating the perimeter of parking areas. Intended to be located near the side of the area, which is over 2.75 mounting heights in width. It produces a semicircular distribution with essentially the same candlepower at lateral angles from 270 to 0 to 90 degrees.
Type V
The type V distribution is ideal for general parking and area lighting applications. Intended to be located at or near the center of an intersection or in a large area, since it has no beams but produces a circular distribution with essentially the same candlepower at all lateral angles.

Glossary of Lighting Terms

ACRYLIC: The generic term for a family of transparent plastics used in making lighting fixture lenses, diffusers and refractors.
AMBIENT: The surrounding environment of a device such as a fixture or ballast. It usually refers to temperature or sound conditions.
AMBIENT LIGHTING: Lighting throughout an area that produces general illumination.
AVERAGE MAXIMUM CANDLEPOWER: The average of the 10 highest readings in a floodlight beam.
BALLAST: A device which modifies incoming voltage and current to provide the circuit conditions necessary to start and operate electric discharge lamps (fluorescent and HID).
BEAM LUMENS: The lumens contained within the beam spread of a floodlight.
BEAM SPREAD: The vertical and horizontal displacement of the beam in degrees, bounded by the angle at which 10% of maximum candlepower occurs. (Maximum candlepower is the highest intensity in the beam.)
BRACKET (Mast Arm): An attachment to a lamp post or pole from which a luminaire is suspended.
BRIGHTNESS: The intensity of the sensation which results from viewing a surface or space which directs light into the eyes.
CANDELA: Unit of luminous intensity.
CANDLEPOWER: Luminous intensity expressed in candelas.
CANDLEPOWER DISTRIBUTION CURVE: A curve showing the variation of luminous intensity of a lamp or luminaire with angle. Generally depicted as a polar curve.
CAVITY: An upper, lower or intermediate zone or region of a room designated as ceiling, floor or room cavity.
CAVITY RATIO (CR): Geometric proportions of the ceiling, floor and room cavities.
Room Cavity Ratio = 5H (Room Length + Room Width)
Room Length X Room Width
COEFFICIENT OF BEAM UTILIZATION: The percentage of light from a floodlight which reaches the seeing task relative to beam lumens.
COEFFICIENT OF UTILIZATION (CU): The percentage of light from a light fixture which reaches the seeing task. It is a function of the fixture, each having its own set of CU's for a wide range of the following factors:
Fixture efficiency, distribution and mounting height.
Room proportions.
Room-surface reflectances
COLOR RENDERING: General expression for the effect of a light source on the color appearance of objects when compared with their color appearance under a reference light source.
CUTOFF ANGLE (of a luminaire): The angle measured up from nadir between the vertical axis and the first line of sight in which the bare source is not visible.
EFFICACY : The ratio of light from a lamp to the electrical power (watts) consumed. Usually expressed in lumens per watt.
EQUIVALENT SPHERE ILLUMINATION (ESI): The amount of light in footcandles produced by a luminous sphere on a seeing task in the center of the sphere that will render the same "seeability" as the raw footcandles render the same task in the specific seeing environment under consideration.
EXPLOSION-PROOF LUMINAIRE: A luminaire which is completely enclosed and capable of withstanding an explosion of a specific gas or vapor that may occur within it and preventing the ignition of a specific gas or vapor surrounding the enclosure by sparks, flashes or explosion of the gas or vapor within. It must operate at such an external temperature that a surrounding flammable atmosphere will not be ignited.
FIXTURE : The device which holds, protects and provides an optical system and power connections for the lamp(s). Fixture usually refers to interior lighting. See LUMINAIRE.
FLOODLIGHT: A projector designed for lighting a scene or object to a luminance considerably greater than its surroundings. It usually is capable of being pointed in any direction and is of weatherproof construction.
FLOODLIGHTING : A system designed for lighting a scene or object to a luminance greater than its surroundings. It may be for utility, advertising or decoration purposes.
FLUX (Luminous Flux): See LUMEN.
FOOTCANDLE (fc): A quantitative unit for measuring illuminance: the illumination on a surface one foot square on which there is a uniformly distributed flux of one lumen.
FOOTLAMBERT: The unit of luminance equal to one candle per square foot
GENERAL PURPOSE FLOODLIGHT (GP) : A weatherproof unit so constructed that the housing forms the reflecting surface. The assembly is enclosed by a cover glass.
GLARE: The sensation produced by luminance within the visual field that is significantly greater than the luminance to which the eyes are adapted.
GLARE, DIRECT: Glare resulting from high luminances or insufficiently shielded light sources in the field of view.
GLARE, DISABILITY: Glare resulting in reduced visual performance and visibility and often accompanied by discomfort.
GLARE, DISCOMFORT: Glare producing discomfort. It does not necessarily interfere with visual performance or visibility.
GRID (Lay-In): A type of ceiling construction where the supporting members (inverted T's) are exposed, and the ceiling tiles and lighting fixtures are laid-in on the flanges of the T's.
HAZARDOUS LOCATION: An area where ignitable vapors or dust may cause a fire or explosion created by energy emitted from lighting or other electrical equipment.
HEAVY DUTY FLOODLIGHT (HD): A weatherproof unit having a substantially constructed metal housing into which is placed a separate and removable reflector. A weatherproof hinged door with cover glass encloses the assembly but provides an unobstructed light opening at least equal to the effective diameter of the reflector.
HIGH BAY: Generally, refers to industrial lighting where high mounting heights may be encountered. Many industrial HID-type fixtures are called high bays.
HIGH INTENSITY DISCHARGE (HID): The term that applies to a family of light sources consisting of mercury vapor, metal halide, and high pressure sodium lamps. Although low pressure sodium lamps are not HID sources, they often are included in the HID category.
HIGH MAST LIGHTING: Illumination of a large area by means of a group of luminaires which are designed to be mounted on the top of a high mast generally 60 feet or higher.
ILLUMINANCE: The density of luminous flux on a surface. Measured in footcandles or lux. The former term for this quantity was illumination.
INVERSE SQUARE LAW: The law stating that the illuminance "E" at a point on a surface varies directly with the intensity "I" of a point source and inversely as the square of the distance "d" between the source and the point. If the surface at the point is normal to the direction of the incident light the law is expressed by E="I/d" .
ISOCANDELA LINE: A line plotted on any appropriate set of coordinates to show all the points on a surface where the illuminance is the same. A series of such lines for various illuminance values is called an isolux (isofootcandle) diagram.
LAMP: A light source. Lamps used for outdoor lighting include HID, incandescent (including tungsten halogen), and fluorescent.
LAMP LUMEN DEPRECIATION (LLD): A factor used in lighting calculations to account for the light loss that takes place in a lamp due to the gradual decay in lumen output over a designated period of burning time. The LLD is contingent upon relamping schedules and the specific lamp involved.
LED: Light Emitting Diode, solid state light emitting phospher (luminous source).
LENS: The shielding or diffuser portion of a fixture, made of plastic or glass, through which the light passes on its way to the seeing task. (Note: Plastic lenses may be manufactured by the extrusion process or the injection molded process. Injection molded lenses are more expensive.)
LIGHTING DISTRIBUTION: Luminaires are classified according to the manner in which they control or distribute the luminous flux.
LIGHT LOSS FACTOR: A factor used in calculating the level of illumination after a given period of time and under given conditions. It takes into account temp., dirt accumulations on the luminaire and room surfaces, lamp depreciation maintenance procedures and atmosphere conditions.
LIGHT TRESPASS: A situation which occurs when, due to lack of adequate beam control, light from a source is distributed onto areas where the illumination is not wanted.
LOUVER: A series of baffles used to shield a source from view at certain angles or to absorb unwanted light.
LUMEN : The unit of light output. Light output is also referred to as light flux.
LUMINAIRE: A complete lighting fixture including one or more lamps and a means for connection to a power source. Many luminaires also include one or more ballasts and elements to position and protect lamps and distribute their light.
LUMINAIRE DIRT DEPRECIATION (LDD): A factor used in lighting calculations to account for the light loss due to the accumulation of dirt on the luminaire. The LDD is contingent upon environment, cleaning schedules and the type of luminaire involved.
LUMINAIRE EFFICIENCY: The ratio of the light leaving a luminaire to that emitted by the lamp, or lamps, used therein.
LUMINANCE (Photometric Brightness): The luminous intensity of any surface in a given direction per unit area of that surface as viewed from that direction. Measured in footlamberts or C/in. All visible objects have some luminance.
LUMINOUS FLUX: The time rate of flow of light.
LUX: The metric unit of measurement of illuminance. The light on a surface of one meter square on which there is a uniformly distributed flux of one lumen. 10.76 lux equal 1 footcandle. Decalux = 10 lux.
MAINTENANCE FACTOR: A multiplier which is applied to account for aging of the lamp and for dirt build-up on the luminaire during the period for which the lamp is in place. Lamp aging and luminaire dirt build-up both reduce light output, the amount of reduction usually increasing with time. In common practice, maintenance factors are applied to initial footcandles to derive the minimum light level on the level on the area being illuminated. Light loss factor includes maintenance factor.
METERCANDLE (lux, lx): The metric equivalent of footcandle.
lux = lumens / square meters
1 footcandle = 10.76 lux
1 lux = 0.0929 footcandles
MOUNTING HEIGHT: The vertical distance between the luminaire and the surface to be lighted. It includes both the pole length and the base (above grade) to which the pole is affixed.
OPTICAL SYSTEM: The lampcavity or environment (including diffusing media) designed as part of the fixture for the purpose of controlling the light output.
OVERHANG: In roadway lighting, the distance between a vertical line passing through the luminaire and the curb or edge of the roadway.
PARABOLIC: The term applied to certain low brightness louver and reflector shapes as derived from the geometric shape (curve) called a parabola where, if a light source is placed at the focal point of the parabola, the resultant emitted light will be redirected parallel to the parabola's geometric axis.
PLENUM: That space between the structural ceiling slab and the finished ceiling. This space may contain air ducts, electrical wiring, etc. It's the area that conceals the housing part of a recessed fixture.
POLYCARBONATE: High quality light stabilized plastic used in making diffusers, lenses and refractors. Very tough and highly resistant to damage from impact of stone, pellets and in some instances, low caliber bullets. Very resistant to UV deterioration.
RECESSED: The term for a fixture mounted in a ceiling opening so that the housing of the fixture is hidden from view. The fixture's lens/door assembly may be slightly protruding, flush or slightly regressed relative to the ceiling surface.
REFLECTOR: A device used to direct the light from a source by the process of reflection.
REFRACTION: The process by which the direction of a ray of light changes as it passes obliquely from one medium to another.
REFRACTOR: A device used to redirect the luminous flux from a source, primarily by the process of refraction (bending the light).
SETBACK: The distance that the center of the luminaire is behind the area to be lighted by that luminaire.
SHIELDING ANGLE (of a luminaire): The angle between a horizontal line through the light center and the line of sight at which the bare source first becomes visible.
SPACING: In roadway lighting, the distance between successive light units measured along the center line of the street.
SPACING TO MOUNTING HEIGHT RATIO: The ratio of the distance between luminaire centers to the mounting height above a reference plane, usually the working plane.
SPECULAR ANGLE: That angle between the perpendicular to a surface and the reflected ray. It is numerically equal to the angle of incidence.
SPECULAR SURFACE: Shiny or glossy surfaces (including mirror and polished metals) that reflect incident light, providing a relatively narrow beam pattern.
SPILL LIGHT: Lumen distributed by the luminaire which are outside the beam spread.
STYRENE (Polystyrene): The generic term for a family of plastics used in the making of fixture diffusers and lenses. Tends to yellow in time due to the effect of UV radiation from fluorescent, HID, and induction lamps.
SURFACE MOUNTED: Any fixture mounted directly on a wall or ceiling is surface mounted.
SUSPENSION OR PENDANT MOUNTED: Any fixture hung from a ceiling by supports (chains, hangers, etc.) is suspension or pendant mounted.
TROFFER: A recessed lighting fixture.
VAPOR-TIGHT LUMINAIRE: A luminaire designed and approved for installation in damp or wet locations. Also described as "enclosed and gasketed."
VISUAL COMFORT PROBABILITY (VCP): An empirical comfort rating of a lighting system expressed as a percentage of people who, when viewing from a specified location and in a specified direction, will be expected to find it acceptable in terms of discomfort glare. Visual comfort probability is related to discomfort glare rating (DGR).
WORK PLANE: The plane at which level work is usually performed, and at which the illumination is specified and measured. Unless it is otherwise specified, this plane is assumed to be a horizontal plane 2.5 ft above the floor.
WRAPAROUND (Wrap): A surface or suspension mounted fixture with a one-piece plastic lens which encloses the lamp compartment on both sides and across the bottom literally wrapping the lamps.
ZONAL CAVITY: The latest and most advanced method used by the lighting industry in the determination of coefficients of utilization for various fixtures.

Frequently Asked Questions

How many lamps does each fixture have?
These fixtures can be custom ordered to suit depending on the HID lamps you want to replace, or the light levels you need. We can make a 2, 4, 6lamp or a 8-lamp fixture.

What kind of lamps do you use?
We recommend high lumen 5000K lamps for the best performance.

How many watts does your fixture have versus HID?
Our standard fixture will operate with approximately 60% more efficiency. For example, a standard 400W HID will use 460 watts with ballast. Our 6-lamp fixture would be a standard replacement that would operate at 218-220 watts.

What is CRI, and how does that make a difference?
CRI stands for Color Rendering Index. This refers to the useable light that the human eye can process. A higher CRI it will make colors much more visibly distinct and pleasing. The CRI on a standard HID can be as low as 65 whereas the CRI with our fixture is into the 80's+.

Are your fixtures UL rated?
Yes, all of our fixtures are UL/CUL approved.

Can your fixture be used in cold/hot weather environments?
Yes, our fixtures can be ordered to perform in extreme weather conditions. It has been used in extreme cold temps as low as --20F.

Are they available in all voltages?
Yes, they can be built to suit any voltage including 347 and 480.

Do you have replacement for 1000 watt HID?
Yes, we use (1) 10-lamp T5 fixture to replace one 1000W-HID fixture.

What kind of warranty do you have?
Each Manufacturer has their own guarantee.

Does this fixture apply for high ceilings, greater than forty feet?
Yes, these fixtures have been tested and approved to drive light to the floor from greater than 50 feet!

What kind of maintenance (cost) is there compared to my HID?
The cost to replace lamps/ballasts is about as much as an HID.

How heavy are your fixtures?
Because of the compact design and aluminum reflector, a standard 6-lamp fixture is less than 20 lbs with ballasts.

Can you get them enclosed, or have shatterproof bulbs?
Yes, we do offer enclosed fixtures.

Is a T-8 fluorescent replacement better than a T-5?
A T-8 fixture will draw less energy than a T-5 and it has lower repair and maintenance costs due to the price of the T-5 lamps. .

What kind of light degradation do you have versus my HID?
Standard HID lamp will lose up to 40% of the original light in the first year; our fixture will retain 90% of its original light at the end of its life.

How do lower operating temperatures affect me?
Every 4 watts saved on powering indoor lighting fixtures means 1 watt saved in air conditioning related costs. Cooler ballasts mean longer ballast & lamp life resulting in less labor and replacement costs.

Do you dispose of my HID's?
Yes, for a minimal fee we can dispose of your old fixtures and ensure that the lamps are properly re-cycled.

How much do they cost, and do you have quantity discounts?
A single 6-lamp fixture is usually less than $50 after rebates and energy savings. Please call us for details.

I don't have any money in my capital budget, what are my payment options?
If you are in the middle of a budget year and funds are tight, we can find low-cost financing packages that range from 1.9% to 6.5% depending on your credit rating. The energy savings will lower the amount due to the utility and you will make up the difference by diverting the funds to the loan payment. Many customers have had a positive monthly cash flow through this option.

Does your price include lamps?
Yes, our fixtures do include lamps, cords and delivery to your space. We use only the highest quality Phillips 850 Alto Series lamps that carry a 2 year warranty.

Is this eligible for a rebate from the utility company?
Yes, most states including Minnesota and Wisconsin utilities offer rebates for this type of energy efficient lighting. Please contact your local utility for availability and details.

Do you recommend replacing fixtures one for one?
No, typically they are replaced based on a new layout... However, in some cases you may be able to replace one for one. Please contact us for assistance with your lighting design.

How long does it take to get my light fixtures?
We always quote 4-6 weeks for delivery, but often times we can get them to you sooner.

Troffer Vs Indirect

Cornell University
Lighting the Computerized Office

Principal investigators:

Alan Hedge, Ph.D, Associate Professor
William R. Sims Jr., Ph.D, Professor and Chairman
Franklin D. Becker, Ph.D, Professor

Department of Design and Environmental Analysis
New York State College of Human Ecology
Cornell University, Ithaca, New York

Initial study report completed October 1989
Extracts and conclusions presented to the
Human Factors Society October 1989

Supplementary study report completed September 1990


Subject: Cornell University

In the last decade, during which personal computers have proliferated in the office, researchers have paid increased attention to lighting. Several studies have investigated the relationship of modern office lighting to the visual health, satisfaction and productivity of office workers.

  • The American Society of Interior Designers found that 68% of employees complain about the light in their offices.
  • A Silicon Valley study pointed out that 79% of VDT users want better lighting.
  • A 1989 Louis Harris survey, the Steelcase Office Environment index, revealed that workers think of eyestrain as the number one health hazard in the office–ahead of radiation, asbestos, even exposure to AIDS.

This degree of dissatisfaction is difficult to ignore. It confirms the need to identify the best methods of lighting the computerized office.

During the 1980's, several studies attempted to quantify the relative merits of the various office lighting methods, including the two most commonly used: parabolic downlighting and indirect lighting. But in many of the studies, the computer workers did artificial tasks under controlled laboratory conditions. No matter how conclusive the findings, their applicability remained open to question.

Without a long-term, real-world field test, there were no definitive answers. However, such a test required a great amount of expense and preparation, plus the full cooperation of a company able to provide the right test facility and the right test subjects.

In the spring of 1988, Cornell University put all the elements in place. This study is the result.

The Structure of the Study

The study was designed to determine whether the selection of a parabolic downlighting system or a lensed indirect uplighting system would make a difference in the visual comfort, satisfaction, health or productivity of computer workers. To minimize the influence of differences in color schemes, furniture, work habits or tasks of individual employees, the researchers sought an installation where a suitably large group of professionals worked in similar offices on a variety of team based computer-oriented tasks, with the lighting system as the only significant variable.

The Lighting Methods Used

These were selected as the best quality commonly used for computer applications in mid 1988.

The Test Facility

The study took place in a Xerox Corporation office in Webster, NY which had already been scheduled for renovation prior to the study. It was occupied by 200 highly-skilled employees who regularly work with computers. At the beginning of the test, the building had several different types of lighting, including a large number of 2' x 4' downlights of a type seldom installed in computerized offices today. The building offered open office areas with partitioned cubicles, 10' x 15' enclosed offices with windows, and 10' x 15' and 10' x 10' windowless enclosed offices.

In mid-1988, the building was renovated. Color scheme, furniture, carpeting and fluorescent lamp type were standardized throughout. Approximately half of the workers received a ceiling-recessed parabolic downlighting system, the other half received the lensed indirect uplighting systems.

June 1989 — The First Study

A benchmark survey taken in late spring 1988, before the renovation, brought answers from 147 workers (92% return rate). The "after" survey taken a year later brought answers from 90 workers (61% return).

Work-related Health Complaints

Daily complaints of tired eyes and eye focusing problems twice as frequent among the parabolic group
The study isolated the frequency of health complaints, one clear indication of productivity.


In the small, windowless offices, symptoms were considerably more frequent within the parabolic group.


Lighting Modifications

Almost half the parabolics in the windowless offices had been altered.
In over three-quarters of the enclosed offices, at least one of the fixtures had been altered, either by disconnecting lamps within the fixture, disconnecting the whole fixture or putting up some form of paper baffle to shield the fixture. Eleven per cent of the fixtures in the open plan showed similar modifications. So far as the researchers could determine, no one attempted to modify the indirect system in any manner.


Parabolic group favors lensed indirect, indirect group preference is almost unanimous for lensed indirect.
The workers were asked to select, from all the lighting systems they'd ever worked under, which lighting system they preferred. Those who'd worked under the new parabolic system voted for the lensed indirect by a clear margin. Only one person who'd worked under the lensed indirect preferred the parabolic.


Effects of Lighting on Work Function

Subjects find parabolic more bothersome than lensed indirect
Because of the high skill level and high creative involvement of the test subjects, both Cornell and Xerox felt that the most important findings of the study would be those which isolated and quantified the workers' satisfaction level. The subjects defined the effects of the two different types of lighting on work functions in general.


June 1990 — One Year Later

The researchers returned to verify their findings after the groups had each had a further year of acclimatization to the two systems. They wanted to earn whether satisfaction levels or the frequency of visual health problems had changed, and to see what actual effects the visual health problems created. The second survey brought answers from 121 workers (82% return).

Work-related Health Complaints

Problems under parabolic cut into worker productivity
In this study, researchers asked workers to report the amount of time they lost from various symptoms. Far more parabolic workers reported lost time, and a high percentage lost over 15 minutes a day. For instance 20% of the parabolic group reported losing more than 15 minutes a day due to eye focusing problems compared to only 2% of the lensed indirect group.

Lighting Modifications

Almost half the parabolics in the whole office area now modified or disconnected
Of the 164 office fixtures in the parabolic portion of the test building, 79, or 48% had been altered. Of that number, ten had been completely disconnected. In the windowless offices, over 75% had been modified (51 of 67). Only one worker in the indirect group modified their lighting.


Indirect group still strongly prefers lensed indirect, parabolic group now prefers indirect by equal margin
One year before, 48% of the parabolic group had preferred the indirect lighting. Now 75% preferred it.


Effects of Lighting on Work Function

Lighting problems now tied to lost work time
Unlike the previous study, subjects were asked to quantify the amount of productive work time they lost due specifically to lighting problems. High percentages of workers under the parabolics reported losing over 15 minutes a day.


Some Questions Raised by the Cornell Study

Any study which produces such important and potentially influential findings will immediately raise questions. The more concerned, interested and informed the questioner, the more specific the questions become. This is a sampling of some of the most commonly asked questions about the Cornell Study.

Were there any differences between the two groups that might have influenced the results?

The respondents in both the 1989 and the 1990 survey showed no significant differences in demographics or work profile between the parabolic and the lensed indirect group. All subjects spent a large portion of their working hours at the computer.

Generally, the subjects were highly-skilled workers whose tasks would better be defined as "creative" rather than "routine." They were involved with graphics, language translation, technical documentation and software development. Many were working with two or three computers at the same station.

Their offices were similar and they were divided up into approximately the same balance between open-plan cubicles and enclosed offices. Almost everything other than the lighting was consistent between the two groups: office temperature, ventilation, noise level, chair comfort, desk space, storage space, privacy, furniture, wall and partition color and so forth.

Was the test structure biased in favor of either system?

The researchers began with certain hypotheses based on earlier laboratory studies. The study report states on page 11, "It was hypothesized a priori that the lensed indirect system would create a more favorable luminous environment, i.e., higher satisfaction, fewer glare problems, better visual health, than that produced by the parabolic system, and consequently one-tailed tests were used for all analyses of questions concerning the effects of the different lighting systems. Two-tailed tests were used wherever analyses were performed in the absence of a priori directional hypotheses."

The survey questions were specifically structured to be neutral. In order to provide the most useful comparative data, the Cornell research team maintained contact with members of other research groups conducting work on office lighting. A number of the questions were identical to those used in survey questionnaires from other recent lighting studies.

One factor made the test something less than a strictly fair comparison. Since this was a real-world study, the workers were free to behave towards their lighting as they would have if no study had been conducted. Almost from the beginning, the workers under the parabolics requested that a high percentage of the fixtures be modified. BY 1990, 6% of the 164 parabolic office fixtures were disconnected entirely and an additional 42% had had one or two fluorescent lamps disconnected.

In the small offices, 76% of the parabolics were modified.

Does the cost differential between the two systems modify the impact of the findings?

From the beginning of the test, the researchers were well aware that the lensed indirect system cost more than the parabolic. Therefore, study results which favored the lensed indirect system over the parabolic wouldn't be meaningful unless they also proved a superiority sufficient to offset the added cost. In this particular installation (a building with no unusual installation problems for either type of fixture), the cost differential for installed fixtures was between $100 and $200 per workstation, depending on the methods used to calculate the cost. The 1990 study revealed that the parabolic workers were losing substantial amounts of productive work time each day due to lighting-related health problems. The following three examples give an indication of the financial impact of that lost time, assuming a conservative installed cost differential of $200 per workstation and an average work loss differential of ten minutes per day.

Economic Impact: Three Scenarios

(Based on 25% salary burden and 8-hour work day)

Installed cost differential per workstation: $200 Installed cost differential per workstation: $200 Installed cost differential per workstation: $200
Annual salary per workstation: $15,000 Annual salary per workstation: $25,000 Annual salary per workstation: $35,000
Average additional time lost/day by parabolic workers: 10 minutes Average additional time lost/day by parabolic workers: 10 minutes Average additional time lost/day by parabolic workers: 10 minutes
Lensed Indirect pays for itself in 6.1 months Lensed Indirect pays for itself in 3.7 months Lensed Indirect pays for itself in 2.6 months

Did the "Hawthorne Effect" influence the results?

Since the findings of the study were based on subjective criteria, the researcher went to considerable length to avoid having the results jeopardized by this much-discussed phenomenon. Earlier studies suggest that workers respond positively to any change in their work environment and the involvement of a researcher.

In this study, the office lighting was replaced as part of a scheduled renovation, and the evaluation questionnaire covered many aspects of the office environment, not just lighting. The researchers were careful to disguise the fact that the study was primarily about lighting, and the 28-question, 169-item survey was presented as an "evaluative study of the three important factors in office design."

Both halves of the building received lighting systems which claim to support computer use considerably better than the previous lighting. Therefore, any influence from the Hawthorne Effect should have been minimal and should have been equal for both study groups.

Why weren't workers shifted during the test so they could experience working under both systems?

This was a real-world test, not a controlled laboratory test. A large-scale movement of employees from one system to the other would have added an unrealistic element to the test. It also would have made it apparent to the subjects that a comparison between the two lighting systems was the true focus of the test.

In fact, because this was a phased renovation, some parabolic workers moved in the indirect area before the parabolic area was completed, which may have had some influence on overall preference figures. Within each group, some changed offices and some didn't. Whether workers moved offices within the group or not was examined statistically and shown to have no significant effect on their opinions about lighting.

Are the results specific to the particular luminaires used in the study?

In the case of the parabolic system, the answer is "no" with minor qualifications. Regardless of the sophistication of its design, direct parabolic downlighting provides a cone of light from an otherwise dark ceiling. Direct lighting creates direct shadows, contrast between the fixture and the ceiling and an environment that is more brightly lit within the cone of light than outside it. The answer is less clear-cut in the case of the indirect system. There is great variation in the ability of indirect lighting systems to distribute light across a wide area. An indirect system like the systems used in the study will provide a superior luminous environment if it can produce even luminance ratios across the entire ceiling. However, one with poor distribution will produce hot spots on the ceiling bright enough to cause contrast and shadow problems similar to those created by downlights. Substituting a lesser system for the one used in the study could have created considerably different results.

Why did the study use indirect luminaires with visible lenses rather than totally indirect fixtures?

The researchers felt it was important to compare the best indirect lighting then available with the best parabolic lighting then commonly available in order to provide as fair a comparison as possible. In the open office areas, the low-brightness visible lenses are claimed by the manufacturer to provide a higher satisfaction level because they provide a higher level of perceived illumination, a contention supported by earlier studies (Bernecker, Penn State University, 1984 and 1986). In the enclosed offices, the lensed indirect fixture provides a superior luminous environment to other commercially available indirect luminaires because the lens provides an extremely widespread distribution designed especially for enclosed areas.

Why were self-reported evaluations of productivity used instead of objective measurements?

At the beginning of the study, representatives from Xerox made it clear that, in their opinion, self-reported evaluation would be the most useful information these employees could provide. The creative nature of the high-salaried job functions created broad variety in the amount and quality of job output. Quality of product meant far more than the number of data bits entered. An attempt to quantify individual output would have been somewhat meaning less in any event, because much of the output in this installation was based on team effort rather than individual production.

Why are measures of preference included, since they seem to have little to do with productivity?

Preference is more important than might first appear. In the positive sense, the very fact that a group of workers prefers a specific type of lighting makes it superior lighting, regardless of whether an outside observer might insist that some other alternative is a "better" system. Preferred lighting contributes to the sense of "a nice place to work" and helps workers feel better about their environment and their job. It also aids in recruitment, since recruiters can point the lighting out as a job benefit. In the negative sense, any irritant in the workplace will contribute to employee dissatisfaction, and at a certain level, dissatisfaction turns to departure. Each personnel expert may place a different dollar value on any phase of the attrition-recruitment-rehiring-retaining cycle, but all agree that any reasonable technique to reduce employee dissatisfaction is a useful and practical tool.

Did differences in light level influence the test results?

Commonly recommended light levels for parabolic systems in computer installations are somewhat higher than those recommended for indirect systems. Normally, parabolic installations have an average illuminance of 50 to 70 fc and indirect installations have an illuminance of 30 to 50 fc. Both systems were installed according to standard practice and to provide average illuminances within the standard boundaries.

© Cornell University, 1991

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