Lighting the Shop

by Bill Tindall

When I started to do more hand tool work in my windowless shop I found that the scattered overhead fluorescent lights did not provide enough light for this detailed work. Furthermore, the flicker, hum and unnatural colors from the lights left me edgy after working under them for some time. I had experienced none of these problems in my former shop that had large windows. My brother-in-law is a lighting engineer at GE and I asked him for help to improve the design of my shop lighting. Now I have a well-lit shop that is pleasant to work in and I can see well enough to do detailed work. The "make-over" cost less than $200. I would like to pass on what I learned about shop lighting from the lighting engineer and the GE publications he provided so that others might benefit. I found that the complaints people have with fluorescent lighting can be eliminated by proper lamp and fixture choices.

To begin, let me explain some terms that are important in discussing and choosing lighting.

Fluorescent lamps - With regard to shop lighting, these are typically straight, tubular lamps used for ambient lighting. Ultraviolet light is produced by an electrical discharge through a gas inside the tube. This invisible light strikes chemicals called phosphors that are coated on the inside of the tube. The phosphors reemit visible light of various wavelengths and intensities depending on the chemicals used to make the phosphor. The appearance of light from the lamp, as well as the appearance of objects illuminated by the lamp, depend on these output wavelengths and their intensities. By manipulating phosphor composition, lamps can be made that simulate about any kind of lighting, from sunlight to incandescent light, and even lamps that promote plant growth. Some phosphors are very expensive to make which is one of the reasons that some kinds of lamps are more expensive than others.

Lamp tubes typically come in two sizes, T8 and T12. The 8 and 12 refer to the diameter of the lamp tube in 8ths of an inch. Government mandates promote replacing the formerly standard T12 format with T8. Expect T8 fixtures and lamps to become more available, and T12 less so. Personally, I would only use the T8 format for a new installation.

Ballasts - Ballasts are located in the fixture and provide the proper voltage for tube starting and operation. Newer electronic ballasts are more efficient than old style ballasts and they don't cause the fixture to hum or the lamp to flicker. Electronic ballasts are highly recommended for shop lighting especially around rotating machinery. Old style ballasts can cause strobe effects because of the 60 cycle lamp flicker. Personally, I am very sensitive to flicker and I find working under the electronic ballast lighting less tiresome. All new T8 fixtures will have electronic ballasts.

PAR Lamps - PAR stands for Parabolic Aluminized Reflector. These are incandescent lamps typically used for illuminating a specific area. Light is produced by a hot tungsten filament usually sealed in an iodide vapor, hence the term "halide", or halogen, lamp (iodine is a halide). The role of the halide is to heal defects in the filament that otherwise would cause it fail. These filaments can, therefore, be operated hotter, which produces a brighter, whiter light. The PAR captures most of the light produced and focuses it into a directed beam. The width of the beam is specified on the package by a written description, for example "spot" or "flood", or by degrees, for example "30 degrees". Spot and 30 degree PARs illuminate a narrower area than flood or 60 degree lamps.

Lumens - Lumen is a measure of how much light a lamp produces. For example, a 3300 lumen lamp produces 10% more light than a 3000 lumen lamp. Lumens depend on lamp wattage and lamp efficiency. In general higher wattage results in more light and higher operating cost.

Foot Candle (fc) - Not all the light produced by a lamp (lumens) will reach the area to be illuminated. Foot candle is a measure of the amount of light actually falling on a specific surface and it is defined as one lumen per square foot. As light spreads from a source one can think of this light illuminating the surface of a sphere. The area of a sphere increases with the square of distance from the light source. So, to a first approximation, the amount of light illuminating a surface (foot candle) will decrease with the square of distance from the lamp. An object 2 feet from a lamp will have 4 times the illumination , fc, that an object 4 feet from the source will experience. To determine the foot candles of illumination at any point in your shop a light meter is required. It may be possible to borrow a light meter from a lighting store to measure light intensity.

Color - The eye is illuminated by light of various wavelengths: red, green, yellow, etc. This light stimulates receptors which send signals that the brain interprets as color. Therefore, the perception of color is a combination of physics (light wavelength) and psychology. This fact is important because it means that physical descriptions of light - wavelength, lumens, foot candles - are not sufficient to describe how light or a lighted object will look to you or me.

Color temperature - All objects emit light. The hotter the object, the shorter the wavelength of the emitted light. We can't see the light from a cool object because it is infrared light. Metal workers refer to objects as red hot, white hot, etc. The color of the hot metal depends on its temperature. In physics, the Kelvin scale (K) is used to measure temperature. It is not important to know the details of this scale, only that bigger numbers mean hotter temperatures. Just as metal workers describe the temperature of their metal with colors, lamp manufacturers describe the color of the light from their lamps with temperatures. An object at 5000K is "white hot", so a 5000K lamp produces white light. A 3000K lamp produces a reddish light. Typical color temperatures encountered for fluorescent lamps are 3000 or 3500K which is a reddish light, 4200K which is white, and 5000K which is like sunlight.

Objects illuminated with a 3500K lamp will appear more red ("warmer") than those illuminated with a 5000K lamp. In this context "warmer" is not a description of the lamp color temperature but rather the psychological interpretation of the colors which can be described as warmer (reddish) or cool (bluish). This example illustrates the interplay of physics and psychology in color interpretation by the brain. I particularly like the effect of illuminating my living areas with 3500K lamps and my shop with 5000K lamps.

CRI - CRI is an abbreviation for Color Rendition Index. Because it is a measure of a person's perception of color, it is not as easy to describe as the quantitative measures given above. For fluorescent lamps that have lower color temperatures, CRI compares how something looks under the fluorescent lamp compared to an incandescent lamp. A value of 100 is perfect. For high color temperatures, for example 5000K, the comparison is to sunlight. Cheap lamps might have a CRI of only 60 and objects will not appear in their "true" colors under such a lamp. Premium lamps will have a CRI of 80 to 90 and cost more because the phosphors to make them are expensive and the lamps are not made in as high a volume.

Lighting the shop - Assuming one's eyesight is normal, or corrected to normal, how well one sees depends on light intensity and possibly (experts don't all agree on this point) on the color temperature of the illumination. It is important to consider both the amount of light (foot candles) at the task as well as the background or ambient light. Bright sunlight is up to 5000 fc, but this amount of light is too intense to work under. A cloudy day is about 2000 fc, while an indirectly lit, sunny room is 200 to 500 fc. About 200 fc is required for detailed work. The background lighting should be at least 10% as high as the light intensity at the task, or the contrast of bright work and dim background will hinder the ability to see detail.

It takes a well-designed lighting system to get 200 fc on the bench or at the vise if there is no natural lighting to supplement the artificial light. Large lighting stores have software to determine the number of lamps needed as well as recommendations for placement. Four foot 2-tube fluorescent fixtures scattered about the shop ceiling easily provide the 20 or so fc necessary for background lighting. The shop floor, walls and ceiling should be light-colored to reflect light back towards the work area. The task area, for example vise or bench top, should be lit from above, the sides and behind. Front lighting causes shadows and glare. So, for example, for task lighting at a work bench or work bench vise, a row of fluorescent fixtures would be placed across the shop ceiling and centered approximately at the bench edge. This row should extend beyond the ends of the bench to provide side lighting. It takes numerous overhead fluorescent lights as well as a light colored background to obtain 200 fc at a bench top. (A 4-tube Toffer fixture on an 8' ceiling will provide nearly 200 fc at bench height directly under the fixture.) An inexpensive way to boost light intensity at a task area to the desired 200 fc is with PAR lamps fastened to the ceiling with adjustable mounts. A 90 watt "narrow flood" lamp will provide 100 fc at a distance of 6' and an illuminated area of about 3' diameter. This lamp is therefore suitable for task lighting. I keep several of these lamps mounted in clip type fixtures and fasten them as needed for supplemental lighting at saws, the lathe, or bench.

An example of a well-lit shop could be a scattering of 4 foot 2-lamp fixtures on the shop ceiling for background lighting. Over the bench, as well as over other detailed work areas such as the saw, there would be one or more Toffer fixtures, four foot 4-tube fixtures, placed to provide light from above, the sides and behind the task. PAR lamps in adjustable mounts would be available to provide supplemental task lighting to reduce shadows and boost intensity. A light-colored floor, walls, ceiling and work surface will reflect otherwise "lost" light back to the task area and there-by reduce the need for primary lighting intensity. I improved the illumination on my bench by 50 fc just by replacing the brown Masonite top with an off white top.

Choosing fluorescent lamps and fixtures - Toffer fixtures are inexpensive and they are good for overhead task lighting. Background lighting can be provided by 2-tube fixtures. Commercial duty ballasts are recommended because they last longer. For new installations, T8 fixtures are recommended because as T12 fixtures are phased out T12 lamps could become difficult to obtain cheaply. If you don't like flicker and hum, fixtures should have electronic ballasts. All new T8 fixtures will have electronic ballasts. Electronic ballasts can be purchased and retrofitted into T12 fixtures. T8 lamps must be operated with T8 ballasts and vice versa. However, if the ballast is changed to a T8, then T8 lamps can be operated in formerly T12 fixtures without further alteration because the pin configuration is the same. There are a bewildering number of ballast sizes to choose from, so you may need help at the store to be sure you get the correct size for the lamps.

Choosing shop lamps - There is a lot of useful information about the fluorescent lamp on the lamp packaging. On one, or the other, will be found color temperature, CRI, lumens, and wattage. The choice of color temperature is a personal one. I like the appearance of a bright sun lit work area so I choose 5000 K lamps. Others may prefer the soft lighting of 3500K lamps, or middle of the road 4200K lamps. To decide, buy some of each and see what you like. Colors can look strange under cheap CRI 60 lamps (often sold as "shop lights") and some people may find that annoying. The more expensive lamps with CRI of approximately 80 will be suitable for most people and applications. Premium CRI 90 lamps are expensive and unjustified for cutting dovetails, but they might have limited application in finishing areas. Lamps will also vary with lumens of light output. If lots of light is the objective and minor operating cost differences less important, buy lamps with the highest lumen rating. For example, 32 watt T12's put out significantly less light than 40 watt T12's. PAR lamp packages will contain wattage, lumens and some indication of the beam spread angle. For PAR lamps, the lumen rating is for the center of the beam. Beware that "high efficiency" lamps are low wattage and hence low light output.

As discussed in this article, proper lighting is a combination of lighting fixtures and lamps as well as their placement and number. The reflection of this light off the surroundings also is important. If there are lighting questions that this article has not covered, consult with the design people at well stocked lighting store. They should be able to provide even more detail on fixtures, lamps and design details.