• Lighting the Small Workshop - by Jack Lindsey

    Lighting the Small Workshop
    By Jack Lindsey

    "Ten years have passed since I wrote the Fine Woodworking article on lighting the small shop," Jack Lindsey explains, but much has changed. Jack comprehensively explores lighting a hobbyist or small industrial shop, drawing on over 25 years of professional lighting experience, covering topics such as fixture and ballast selection, lamp life, and color when employing fluorescent lamps.

    Introduction

    Ten years have passed since I wrote the Fine Woodworking article on lighting the small shop. While the principles it contained remain valid, there have been changes in lamps and ballasts resulting from technological advances, and legislative mandates have outlawed some of the most popular lighting products. Magnetic ballasts for most lamps are being phased out, and the mainstay of fluorescent lamps, the T12’s, are meeting the same fate. Some of the common general service incandescent lamps have also been outlawed in favor of more energy efficient fluorescent and LED lamps. The replacement products are for the most part more energy efficient although in some instances they are inferior in terms of performance and generally have a much higher first cost. We have no choice but to use them, and choosing the ones we use carefully can result in better performance and lower overall costs.


    This article will focus on lighting the hobbyist or small industrial shop with ceiling heights of 16’ or less using commonly available T8 lamps, and strip or industrial type fixtures. The design method used in this article may also be used for T5 HO lamps with the caveat that they are several times brighter than T8’s and may cause objectionable direct glare if located within the field of view. Their use should be confined to shops with high ceilings. The minimum height will vary with the size of the shop, with large shops presenting the greatest potential for glare since more ceiling area will be within the field of view as the size of the shop increases. As a general rule I prefer to see them at a minimum height of 14’. Be aware that T5 HO lamps are currently about 5 times the cost of T8’s, and fixtures cost almost twice as much. This is somewhat offset by the need for fewer lamps and fixtures. If you are considering using these lamps I suggest a trip to your local big box home improvement store to see them in operation. If you are satisfied that the brightness is acceptable the next step is to determine how many fixtures will work in your shop, and compare the economics between T5 and T8 systems.

    Twenty eight watt T5 lamps are not included since their performance characteristics are similar to T8’s but they are significantly higher in cost. HID lamps in wattages suitable for industrial use are very bright and should be mounted at heights of 18’ or more so they are not included. Light emitting diodes (LED’s) are an emerging technology and are also omitted.

    Over the years I have done many posts on this and other forums suggesting the installation of “x” number of fixtures spaced “y” feet apart, and you may have seen one or two where I explain some of the theory behind it. This article will differ in that it will enable the reader to easily determine the number of fixtures that are needed, and provide guidelines on how to lay them out in the space. It will contain some theory but concentrate on the mechanics so almost anyone can follow the blueprint to light a small shop. No one will come out of this a qualified lighting designer but that's not the objective. I’m just trying to improve on what can be done through trial and error, and try to combat some of the misconceptions about lighting that I see on a regular basis on the forums.

    We’ll start with some lighting terminology that will be needed as we progress through the steps to design your own lighting system. Then a brief discussion of how much light we really need based on the kinds of things we do in our shops and the age of our eyes.
    Then we’ll get into the meat of the subject: the lamps, ballasts, and fixture types that best meet our needs. We’ll talk about lamp characteristics, circuit types, lamp life, and color temperature and color rendering index. Electronic ballasts are now the norm but there are distinct differences between many of them. For the most part we are at the mercy of the fixture manufacturers since they select the ballasts they install but we do have the option of using another fixture if necessary. This article will discuss the important ballast characteristics that should be considered when we buy a fixture.

    There are many different kinds of fluorescent fixtures. Some are well suited for lighting our shops. Others are not. I’m not going to engage in a discussion of brand names but I will go over things to consider when picking a fixture. And we’ll concentrate on fixtures that are readily available through the big box retailers and lighting distributors.

    Finally, we will go through a simplified method of determining how many fixtures are needed using a method I developed and taught in my lighting classes to help contractors and lighting sales people come up with a preliminary number of fixtures to help qualify prospective customers. While the method isn’t precise it is sufficiently accurate for a small shop.

    Note that this discussion assumes that we will provide uniform illumination throughout the shop. Why do this instead of just lighting the work areas? Simple. Fluorescent fixtures tend to have a fairly wide distribution of light, space is usually at a premium so we locate machines close together, and we move machines periodically about the shop.

    The last step is laying out how the fixtures will be installed. Should they be installed in continuous rows or as individual fixtures? How far apart should they be? How close should they be to the walls? Should they be mounted directly to the ceiling or suspended?
    The article is arranged in sections, each covering an individual topic. If you already know how much light you want, what equipment to use, or how you want to light the space you can simply skip those sections and go directly to your area of interest.

    Dave Anderson, a Moderator of the forum, asked that I include my qualifications to write the article so here goes. I retired as a Senior Engineer from a major west coast electric utility where I specialized in lighting for over 25 years. My main responsibilities were providing assistance to commercial and industrial customers on lighting, training company personnel, and evaluating new lighting equipment. I taught evening classes in lighting design at a couple of community colleges and a course in Illumination Engineering at a state university, and wrote “Applied Illumination Engineering” which was used as a text for those classes. I also wrote a monthly column on lighting for Electrical Contractor magazine, and have authored and presented numerous technical papers on lighting to IEEE, IESNA, and AEE. I’ve served as an advisor to the California Energy Commission on the development of the lighting portion of their energy code and as a charter member of their Advance Lighting Professional Advisory Group. I am a Fellow of the Illuminating Engineering Society of North America and have served as President of that organization.

    Now, on to lighting our shops.

    FUNDAMENTAL LIGHTING UNITS AND RELATIONSHIPS

    Yeah, this is the boring part. When I took my first class in lighting we spent several hours going over terminology, definitions, and their relationships. I was bored to tears and spent most of that class period wishing I was fishing. It didn’t take long to realize, though, that it was going to be tough if I couldn’t comprehend the language of lighting. We’re only going to cover three basic units in this discussion though, so it won’t be too bad. And we’re going to discuss them in plain English, not scientific terms, so leave your physics books on the shelf.

    CANDELA The first building block is the “candela” (cd). It is the unit of luminous intensity and allows us to assign a number value to the brightness of a light. The higher the number, the brighter the light. An ordinary wax candle flame has an intensity of 1 candela when viewed from any angle. It is used in industry as a basis for many lighting calculations.

    LUMEN The lumen (lm) is the basic unit of a quantity of light. That’s not the technical definition but it’s pretty close and is a lot more understandable. The light output of a lamp is rated in lumens. The common 100 watt incandescent in your table lamp produces about 1750 lumens. Many 4’ T8 fluorescent lamps are rated at 2800 lumens.

    FOOTCANDLE The footcandle (fc) describes how much light is striking a surface. More light equals more footcandles. By definition one footcandle is equal to 1 lumen of light striking one square foot of surface area. The footcandle is being replaced by the SI unit of illuminance, the lux. One lux is equal to 1 lumen of light striking one square meter of surface area. A square meter is about 10 square feet so 1 fc is approximately 10 lux.

    The SI system has been slow to gain acceptance in the United States so this discussion will be based on footcandles and feet.


    Now let’s explore how these units are related and how we can use that knowledge to light our workshops. Let’s light a common candle and place it in the center of a plastic sphere that has a radius of 1 foot as shown in Figure 1. Now divide the sphere into one square foot areas and measure the amount of light striking each square foot. By definition that amount is one lumen. It is equal to the amount of light falling on an area of 1 square foot, all points of which are 1 foot away from the light source. Since our sphere has a radius of 1 foot it has a surface area of 12.57 square feet and our candle with an intensity of 1 cd produces 12.57 lumens. This helps put the light output of a lamp in perspective. It takes a lot of candles, about 139, to equal the light output of a 100 watt incandescent lamp.



    Figure 1. Relationships between candelas, lumens, and footcandles. When a light source of 1 cd intensity is placed in the center of a sphere with a 1 foot radius, 1 lumen of light will strike 1 square foot of surface area. This produces a lighting level of 1 footcandle.
    Courtesy of IESNA (Picture of candle added for clarity)


    HOW MUCH LIGHT DO WE NEED?

    Rather than spend several pages discussing the complexities of evaluating visual tasks and quantifying illuminance requirements based on age, the need for speed and accuracy in our work, or the influence of the reflective characteristics of the things we work on I’m simply going to give you my opinion based on over 25 years in the profession. Typical hobbyist and small commercial woodworking shops should be lighted uniformly to levels of 50 or 100 footcandles (fc). Fifty fc for shops with young workers (age 25 or less) where there are no difficult visual tasks like intricate carving, fitting of small precision parts, etc.

    For those of us over 25 or in shops with more detailed work as mentioned above I recommend 100 footcandles. If we are performing very difficult visual tasks like intricate carving additional light may be needed. This is typically provided by a small task light. The recommended values fall within recommendations published by the Illuminating Engineering Society of North America (IESNA) in their 2011 Lighting Handbook. Note that these are nominal values and a variation of 10 to 20% isn’t significant. Why? Because the human eye is an amazingly adaptable instrument. We can see at night in a parking lot under 1 fc or less or on a sunny mountain top with over 10,000 fc at high noon. Small variations in lighting levels are insignificant in terms of visual performance.

    FLUORESCENT LAMPS

    Unlike incandescent lamps which produce light by heating a thin tungsten wire filament to a very high temperature, fluorescent lamps don’t have a filament and operate quite differently. They consist of a glass tube that has had virtually all the air removed and small quantity argon, neon, or other specialized gas injected. Some metallic mercury is added, a wire coil called a cathode is inserted into each end, and the tube is sealed. See Figure 2. The internal pressure is very near a vacuum so the mercury is primarily in a gaseous state, with molecules of mercury floating independently within the tube.





    Figure 2. Cutaway of a typical fluorescent lamp showing component parts.
    Courtesy of IESNA


    While the cathode may resemble an incandescent filament its function is quite different. It acts as a terminal for an electric arc that passes through the tube. In operation electrons in the arc stream collide with electrons in the mercury atoms causing some of them to be temporarily displaced. When they jump back to their proper locations they give up the energy they took on from the collision. A little of that energy is in the form of visible light but most of it falls in the ultraviolet region, 253.7 nanometers for those with inquiring minds. Figure 3 illustrates this sequence of events.

    The cathodes are coated with an emission material that provides the electrons for the arc stream. As the lamp operates the material is boiled off the wire so the supply of electrons is continuous. When all of the material is evaporated from either cathode the arc cannot be maintained and the lamp fails.

    The inside of the tube is coated with a powder, called a “phosphor”, that converts the UV energy to visible light. Different phosphors are used to produce different colors of light, and the process is much more efficient that heating a wire. Figure 3 illustrates this sequence of events.



    Figure 3. Principle of operation of a fluorescent lamp. An electron in the arc strikes an electronin the mercury atom causing it to jump to a higher energy level. When the electron jumps back to its original level the energy it took on in the collision is released in the form of ultraviolet radiation which strikes the phosphor on the inner surface of the tube and excites it. This produces visible light. Courtesy IESNA

    Why is all this important? Because it will be used later in the discussions of color and ballasts.

    This discussion will focus on T8 lamps. The “T” indicates that it is a tubular lamp and the “8” denotes the diameter in 1/8ths of an inch so a T8 is 1” in diameter. Quite a bit smaller than the 1 ½” T12 lamp that was the industry standard for decades. They are available in lengths ranging from 2’ to 8’ for general lighting however shorter lengths are made for some specialized applications. Four foot lamps are the most common and are preferred for the typical hobbyist or small industrial shop for two good reasons: they are lower in cost, and much easier to handle than 8’ lamps – especially when atop an 8’ or 10’ ladder.

    COLOR

    The color temperature and color rendering index of a fluorescent lamp are probably the two most discussed and least understood lighting topics discussed on the forums. They are interrelated and will be discussed together.


    Color Temperature

    The visual color of a light source is described by its color temperature. Imagine a bar of steel. At room temperature it is a dull grey. Now imagine that the bar is placed in a blacksmith’s furnace. As the temperature of the bar rises it begins to change color. First a dull red, then as more heat is applied it progresses to a bright cherry red, then orange, yellow, and finally a bluish white. If we measure the temperature of the bar at any of the colors we can then describe the color of the bar in terms of its temperature, and each and every time we heat the bar to that specific temperature it will appear to be the same color. For example, if we heat the steel to a temperature of 4941 degrees F it will appear to be a warm, soft white with an almost imperceptible tinge of yellow. This will be about the color of a 200 watt incandescent lamp or a 3000K fluorescent.

    The example, while accurate for purposes of understanding, isn’t scientifically correct. In practice we use a theoretical device called a blackbody radiator instead of a bar of steel. The blackbody will perfectly absorb and then reradiate all energy that strikes it. An incandescent filament almost perfectly matches the blackbody within the visible portion of the spectrum so we have visual basis for comparison.

    Note in the example I cited a temperature of 4941 Degrees F for the bar yet compared it to a 3000K fluorescent lamp. That’s because we don’t use the F scale to describe color temperature. We use the Kelvin scale, also known as the Absolute scale. Note that while the temperature in F or C is stated in degrees the temperature for the K scale is stated in Kelvins, not degrees Kelvin. The Kelvin scale uses the same gradients as the Celsius scale but has its zero point at -273C. The two temperatures, 4941 F and 3000K are the same. Figure 4 shows a comparison of the three scales.




    Color temperature also describes the visual impression of the space in terms of warmth or coolness. A 3000K lamp imparts a feeling of warmth while a 4100K lamp is cool. Temperatures of 5000K and above tend to psychologically feel cold and sterile.

    Color Rendering Index

    Color temperature only tells part of the story about how the light from a lamp will make an object look. Unfortunately there isn’t a perfect way to describe it but we do have a system that helps. It isn’t ideal but it’s all we have. It’s called “color rendering index” and it describes how well the spectral distribution of the lamp compares to that of a blackbody radiator, typically at eight specific colors. As differences widen between the test lamp and the blackbody the CRI will begin to decrease. In general a higher CRI will provide better color rendering. It is important to note that the lamp and the blackbody must operate at the same color temperature.

    Comparisons of CRI’s between lamps of different color temperatures will be meaningless. For example, incandescent lamps have a CRI of 100 throughout their range of operating temperatures from dimmed to full brightness yet their ability accurately render colors varies widely as the color temperature changes. At 1800 K the lamp produces mostly red light so reds look great and blue colors will be washed out. Increase the temperature to 3000K and blues will look much better and reds will also good. At 4100K blues improve but reds begin to wash out.

    Selecting a lamp color for your shop is a matter of personal preference and how much you are willing to spend. There are no right or wrong answers. Some stores have displays of several lamp colors and they can be helpful. If you can’t find a display and don’t already have a preference, 3500K is somewhat neutral and not a bad place to start.

    Note that there has been no discussion of the screw in compact lamps. They have been purposely omitted because they are simply not a viable light source for lighting an entire shop. If you have a need for supplemental light at a specific location or are looking for a screw in replacement for an incandescent lamp they may be fine, but not for lighting an entire shop. Compared to a T8 they are less efficient, have a shorter life, more expensive.

    BALLASTS

    Once an electrical arc has been initiated in a fluorescent lamp, the lamp exhibits a negative electrical resistance characteristic: the resistance to current flow through the lamp decreases as the current increases. This “run-a-way” current would destroy the lamp in a few seconds if allowed to continue. An auxiliary device, called a ballast, is required to prevent this condition. In addition to limiting current the ballast provides the proper voltages to start and operate the lamp.

    Most older ballasts, referred to as “magnetic”, contain a current limiting transformer, a power factor correction capacitor, and a thermal safety switch. The transformer consists of coils of copper or aluminum wire wound around a steel core to alter the output voltage. These coils have resistance therefore some electrical energy is lost in the form of heat. This is bad since the heat costs money on your power bill, and excessive heat shortens the life of the ballast, particularly when it is enclosed in a fixture.

    Magnetic ballasts for most lamps have been eliminated by legislative mandate and have been replaced with ballasts using electronic components to perform the required functions. There were some problems with them during their early days in the 1980’s and ‘90’s but those have been resolved and most current electronic ballasts are highly efficient and very reliable. They have lower internal power losses since they do not utilize transformers. Another, seldom discussed advantage of electronic ballasts is they generally drive lamps at frequencies of 12 kHz or higher which increases the efficiency with which the phosphors produce light.

    Rapid Start vs Instant Start Ballasts

    There are many different types of electronic ballasts on the market and they vary widely in performance characteristics. As previously mentioned at the beginning of the discussion of fluorescent lamps, the cathodes which serve as terminals for the arc contain an emission material to provide electrons for the arc stream. These electrons must be heated to boil them off the cathodes. This can be done in either of two ways: independently heating the cathode by continuously applying a low voltage to it, or by using a high voltage to blast electrons off the coils and then relying on heat created by the arc stream to maintain the cathode temperature. The first method is known as “rapid start” and the second as “instant start”. Rapid start ballasts provide a gentler boil off of electrons compared to instant start so lamps tend to last longer when operated in the rapid start mode. The downside is that the independent cathode heating uses power that adds to operating costs so if all other factors are equal a rapid start system will cost slightly more to operate. There are premium instant start ballasts available that employ circuits to soft start lamps and significantly extend lamp life.

    Unfortunately we have no control over the specifications for the ballast in the fixtures we buy so we take what we can get, estimate the number of fixtures we need based on generalities, and pay the power bill. Fortunately, for a small shop, that produces sufficiently accuracy for the design process and the differences in cost are usually insignificant.

    One final thought on ballasts. Many of the inexpensive shop lights use the minimum components needed to operate a lamp to keep costs down. Because of this they may significantly shorten lamp life and may fail prematurely. I don’t recommend them.

    LAMP LIFE

    The life of a fluorescent lamp ends when all of the emission material, previously discussed, evaporates from one of the cathodes. This is governed by the ballast type and quality, and the number of operating hours each time the lamp is started. Frequent starts and short burning cycles shorten life while longer cycles extend it. Most ballasts used in industrial grade and medium to high quality consumer products can be expected to drive lamps within the lamp manufacturer’s specifications. Inexpensive ballasts used in low priced shop fixtures may not provide the correct voltage and current characteristics and result in low light output and short lamp life.

    Rated life doesn’t mean that each lamp will last that long. It means the point at which 50% of the lamps in a large sample will have failed and the remaining 50% will still be in service. Failures can be expected to begin at 40% of rated life and accelerate to 50% failures at rated life. Theoretically for each lamp that fails early another lamp will last a corresponding time past rated life.

    Note that I haven’t put an hour figure on rated life. That’s because it varies greatly by 4’ or 8’, instant start vs. rapid start circuitry, premium circuitry in the ballast, and the number of hours the lamp is operated per start. In general 4’ lamps have longer lives than 8’ lamps, rapid start lasts longer than plain instant start, and premium instant start may last the longest. Unlike the days when I entered the lighting profession and you simply went by the single number in the lamp catalog it’s now necessary to consult lamp and ballast catalogs for accurate information. If you are buying a fixture off the shelf at a big box retailer just assume 20,000 hours for a 4’ lamp and 15,000 for the eight footer and check the manufacturer’s literature if you want a more accurate number. This assumes operation for 3 hours per start. Life will be shortened if you turn them off more frequently and extended with longer operating hours. Sorry to be so vague but we would have to append a lot of catalog pages to the article to cover all the possibilities.

    FIXTURE SELECTION

    There are two fixture types that are well suited for our shops: strips and industrials. A strip is simply a white channel that contains the ballast, is equipped with a white cover, and has sockets to hold the lamps. It is the least expensive and is well suited for mounting directly to a finished ceiling. It is recommended that the ceiling be painted a light color, preferably white, to reflect light down to the work area.
    An “industrial” is a strip fixture that is equipped with a reflector to direct light downward. It is recommended for use on unfinished ceilings or when fixtures are to be suspended below the ceiling. The reflector may be white painted metal or specular aluminum. Some reflectors have slots, called “apertures” that allow air to flow past the lamps and through the fixture. The air flow helps keep lamp and fixture surfaces cleaner by carrying dust in the air out of the fixture instead of letting it build up. It also reduces heat buildup around lamps and in the ballast compartment. This increases light output and extends ballast life. The apertures also allow some light to pass through to illuminate the ceiling and help reduce the psychological feeling of working in a cave. They are generally a better choice than reflectors without apertures.

    Other fixture types that I have seen recommended on forums include “wraps”, “troffers”, and other office type fixtures. A wrap is simply a strip fixture that has a plastic lens enclosing the lamps. Troffers are the recessed fixtures we see in most offices and some retail establishments. They are equipped with a lens or louvers to shield lamps from direct view and direct light in specific directions. Neither type is recommended for use in woodworking shops since the lens adds two surfaces, the inside and the outside, that will accumulate dirt and decrease fixture performance. The lens also traps heat which can adversely affect lamp performance. Typical fixtures are shown in Figure 5.




    Figure 5. Typical fixtures. From left to right: industrial with reflector, strip, and wrap.
    Strips are used when mounted directly to a light colored ceiling. Industrials are best
    for mounting to joists when there is an unfinished open ceiling, or when fixtures
    are suspended from higher ceilings. Wraps are not recommended for shops due
    to dirt buildup on the plastic lens.
    Courtesy IESNA

    A final thought on fixtures. You may be tempted to use a strip instead of an industrial with a reflector if your shop construction calls for the industrial. Yes, the strip is lower in cost but it won’t perform well unless it is mounted on a white painted ceiling.


    ESTIMATING HOW MANY FIXTURES ARE NEEDED

    The first step is to decide what lighting level you want. As previously noted I recommend 100 footcandles unless you are under the age of 25 and will be performing work that is not demanding and is easy to see. If that’s the case you may get by with 50 fc or less. Since 100 fc is a more common recommendation that is the value we will use in this example.

    Next let’s calculate how many lamps will be needed using the simplified rule of thumb method which says that 50% of the fixture lumens will reach the work plane when installing open fixtures like strips or industrials in rooms with fairly light colored ceilings and walls. If using enclosed fixtures, which I generally don’t recommend for shops, the figure is closer to 40%. Why only 50%? There are several reasons. First, not all of the light gets out of the fixture. Some hits fixture surfaces where it is absorbed and lost. Some light hits the walls and other building surfaces where it, too can be absorbed. That loss can easily be 25% or more. And over time the light output of a fluorescent lamp decreases due to a deterioration of the light producing phosphors and a buildup of tungsten which evaporates from the cathodes and deposits on the bulb wall. On average we can expect the typical T8 system to lose 10% to 15% of its initial output due to depreciation within the lamp.

    Another significant loss occurs from the buildup of dirt on fixture and lamp surfaces. If you doubt this simply wipe a lamp that has been operating in a workshop for a year or more with a white cloth. Over time you can easily lose an additional 10% to 20% even in a relatively clean shop. Dirt accumulation on walls and ceilings accounts for additional losses.

    Now that we have accepted that we are going to lose light over time let’s see how many fixtures are needed. For this example let’s assume a 1500 square foot shop with a 10 foot ceiling painted white, and white walls.

    The footcandle was previously defined as lumens of light per square foot. To provide 100 footcandles we need 100 lumens per square foot times 1500 square feet, or 150,000 lumens at the work surface. Since only half of the lumens on the ceiling make it down to the work surface we need twice as many on the ceiling, or 300,000 lm. Assuming a 32w T8 lamp rated at 2800 lm we need 300,000 lumens divided by 2800 lumens = 107 lamps. Each 8’ fixture contains 4 lamps so we need 27 fixtures. In math terms this takes the form:

    # fixtures = (desired fc) x (shop area) x (2) / (lumens per lamp) x (# lamps per fixture)
    = (100 fc) x (1500 sq. ft.) x (2) / (2800 lumens) x (4) = 27 fixtures
    How will that fit into the space? If we mount the fixtures end to end in continuous rows we can fit 6 fixtures in a row with one foot left over at each end. In reality a 50’ long building won’t have 50’ of free space inside since the walls take up some of that 50’ so 6 fixtures is a good fit. The next question is how many rows. Twenty seven fixtures divided by 6 = 4.5 rows. We can’t realistically install half a row so we have a choice of 4 or 5 rows. Before making that choice let’s see how they might fit in the space.

    Good design practice calls for spacing rows even distances apart with the distance from the walls to the closest row 1/3 to ½ the spacing between rows. I usually calculate it for ½ and make adjustments if needed later. For the first option, 4 rows, divide the total distance, 30’ for the example, by the number of rows, so 30/4 = 7.5 feet. This is the spacing between rows and the spacing from a wall to the first row is ½ that, or 3’8”. The 3’8” will actually be less, closer to 3’ due to wall thickness but that’s ok. It’s a good idea to have some fixtures close to walls because we frequently put machines long them. That’s where the electrical outlets usually are. The other option is to use 5 rows spaced 6’ apart and located about 3’ from the walls. The layouts are shown in Figure 6.



    Figure 6. Two possible layouts for the example shop. Option 1 is uses fewer fixtures and will result in substantial savings in both first cost and ongoing O & M costs. It will, however, require occasional cleaning of fixtures to maintain lighting levels.


    When determining the spacing it’s a good idea to avoid unusual distances such as 7’ 2 ¾”. Just round it to 7’ and make adjustments next to the walls.

    The next step is to see if the layouts meet the criteria for providing uniform lighting without dark spots in between fixtures. That’s done using something called the spacing criteria, or SC. It provides the maximum spacing between fixtures for uniformity based on the mounting height of the fixtures above the work surface. It is found from manufacturer’s catalogs or specification sheets and is given as two values, one for spacing parallel to the lamps, and one for perpendicular. We are mounting the fixtures in continuous rows so we need be concerned only with the perpendicular spacing. Since you probably won’t have access to the data, values of 1.5 perpendicular and 1.3 parallel are reasonable assumptions.

    For the example we have a 10’ ceiling. Most workbenches or tables are about 3’ high so the mounting height above the work plane is 7 feet. The maximum spacing is then 1.5 x 7’ = 10.5 feet. Both of our proposed layouts use closer spacing so either is acceptable in terms of uniformity. It is important to understand that the spacing criteria are not a design guide to determine optimum spacing. It is only used to determine the maximum spacing to achieve a uniform distribution of light within the space.

    Note that this example assumes fixtures will be mounted in continuous rows. This is generally the preferred method since it provides good light distribution and minimizes electrical wiring costs since the fixtures themselves are used as the raceway and it is only necessary to provide power to one end of the row. An exception might be when lower lighting levels are desired and fewer fixtures are needed.

    We are now at a decision point. The estimate calls for 27 fixtures but that doesn’t fit well into the space. Option 1 calls for 24 fixtures while the other calls for 30. Do we put in 3 too many or 3 too few. I’d go with 24. There’s a considerable savings in first cost and ongoing costs for electricity, and fewer replacement lamps over time. We can easily maintain the lighting levels we want by occasionally cleaning the lamps and fixtures. That’s because we factored in a decline in light output due to dirt accumulation on the lamps and fixtures, and the gradual depreciation in light produced by the lamps. These losses can be recovered by cleaning and relamping. Routine cleaning once every year or two will help maintain lighting levels in your shop. Note that when the system is new and everything is clean the lighting levels will be higher than the design level. That’s normal.

    The information provided in this paper can’t cover all of the possible configurations of shops or all of the various tasks we perform in them, but it does contain guidelines that should be of help for most of them.


    Acknowledgments


    In closing it is only proper to thank those who have been involved in bringing the idea to print. To Ken Fitzgerald, Forum Moderator, for his tireless efforts to overcome limitations on posting long articles on the Forum and taking the lead in the actual posting. This article would not be on the Forum without Ken’s considerable efforts. To Michael Mayo for lending his IT expertise, to Jim O’Dell for suggesting in the beginning that I write it, and to Dave Anderson, another Forum Moderator, for jumping in at the start to suggest how it might be done. And thanks to all of them for reviewing and commenting on the content and format. Finally, a big thanks to the Illuminating Engineering Society of North America for providing most of the illustrations.

    This article was originally published in forum thread: Lighting the Small Workshop - by Jack Lindsey started by Jack Lindsey View original post
    Comments 89 Comments
    1. Todd Burch's Avatar
      Todd Burch -
      This is an excellent article.

      After reading it, however, I was totally bummed, because my estimate for shop lighting went from an "off the hip" guess of $1000 to a pretty realistic, no surprises, plenty of light, $6500 estimate. Not sure whether to jump for joy or cry. But, I feel if I follow the principles outlined here, I'll have good lighting.

      Todd
    1. Ken Fitzgerald's Avatar
      Ken Fitzgerald -
      Todd,

      I used Jack's original article for my shop lighting and dearly love the results. I have gotten many compliments by visitors about the lighting!
    1. Todd Burch's Avatar
      Todd Burch -
      Quote Originally Posted by Ken Fitzgerald View Post
      Todd,

      I used Jack's original article for my shop lighting and dearly love the results. I have gotten many compliments by visitors about the lighting!
      Picture please!
    1. Ken Fitzgerald's Avatar
      Ken Fitzgerald -
      Todd,

      In the following thread, scroll down to post #32 where you can see 3 photos showing the layout. My shop is 32x24 with 9' 8"ceilings.

      http://www.sawmillcreek.org/showthre...e-turners-here
    1. Joel Turner's Avatar
      Joel Turner -
      This thread has been very beneficial as I plan out my basement shop. I'm looking for feedback on my calculations to see if I understand the concepts presented. All fixtures are 4ft, 4 bulb, 2800 lumens with 8.8 ft ceilings unfinished.

      The basement area I want to light is approximately 456 square ft broken into two sections of 289 square ft and 167 square ft. Mechanicals and the staircase divide the two halves. When I calculate my lighting for the 289 sq ft area, I came up with 5 fixtures. Since one part of this area is wider than the other, I'm fine with the idea that the wider section will have three 4ft fixtures and smaller area will have 2 fixtures. As the room is approximately 21.5 ft long, I came up with the first row 6 ft away from the wall with the spacing between the two rows about 12 ft. Does this seem right?

      For the 167 square foot area, I calculated three fixtures. The area is 18' X 9. Does it make sense to have three rows with one fixture each? I was thinking the first fixture 3 ft away from the wall with 6 ft spacing.

      Any input would be greatly appreciated.

      Thanks,

      --Joel
    1. Jack Lindsey's Avatar
      Jack Lindsey -
      Sorry for the delay in responding, Joel, I've been off the forum for a couple of days. If I understand your shop correctly you have two areas, one approximately 13.5 feet by 21.5 feet (289 sq ft) and the other 9 ft by 18 ft (167 sq ft).

      The 4' 4 lamp fixture will be ok for the 167 sq ft area. I suggest running them parallel to the 9' wall. Locate the first fixture 3' from the wall with a spacing of 6' between fixtures.

      You will get much better results in the 289 sq ft area if you use 2 lamp fixtures instead of 4 lamp. Install 2 rows of 5 fixtures each running parallel to the 21.5' wall. Space the rows about 7.5' apart, and 3' from the walls. Using a single row of 4 lamp fixtures will put them too far from the side walls and you will have dark spots.

      Hope this helps.

      Jack
    1. Joel Turner's Avatar
      Joel Turner -
      Hi Jack,

      I've been off line for several weeks myself, but I really appreciate your feedback and suggestions. I will try the configuration you suggested and fill in with task lighting where needed.

      Thanks,

      --Joel
    1. Scott Vaughan's Avatar
      Scott Vaughan -
      Attachment 294307I just got this from Duke Power and thought it would add to the information here with regards to T8 and LED lighting
    1. Judi Watson's Avatar
      Judi Watson -
      Great article, thank you Jack. The ceiling is open in my shop at about 92", I'll be setting up better lighting next week, moving a few fixtures so I can add a few. Thorough, thoughtful and thought provoking, thanks again.
    1. Jack Lindsey's Avatar
      Jack Lindsey -
      You're welcome, Judi, I appreciate your feedback. Glad it was of help.
    1. John Cavette's Avatar
      John Cavette -
      Quote Originally Posted by Jack Lindsey View Post
      You're welcome, Judi, I appreciate your feedback. Glad it was of help.
      Hi Jack

      My name is John and I'm a new B, I have read both your first and second articles and am very impressed with your work and help with and for others. From what I see, you love what you do. And that is a wonderful thing.
      I do have a "FEW" questions I'm hoping you can help me with though.

      Back in 08 I put up a 30x30 shop with a bonus room above and extended one wall out on the ground floor out with a 10x16 foot wing making one wall 46', what was suppose to be a sort of office area that ended up being more of a storage area for hording STUFF.

      The actual inside floor dimensions in the shop area are 29x29 do to the 2x6 walls. The inside walls are insulated and covered with a milky white fire retardant plastic wrap, but otherwise unfinished, with very little reflective value if any. The 9' inside ceiling of the shop is also unfinished do to utilities like electrical conduits, hot /cold water and natural gas for the radiant heat in the shop floor. Also the fact of all the multi layer 2x10 truss's spanning the 30' from left to right across the shop that I can't drill holes in. Also easy maintenance for repairs. The rear wall of the shop has a stair well that is 4' x15' across it, that cuts out a 4'x15' floor area that also cuts my square footage down 60sq.ft.then the 60 sq. ft. section next to that that's sorta out of the square of the room as far as a pattern of light fixtures. Sort of a inset if you will. So that's a long winded description of the area of my lighting project.

      My intention was to suspend the lights up in the cavities between the truss's and floor joist just enough to keep from loosing any light from the truss's and joists and harms way. One of my problems is that the truss's at the front and rear, run from left to right, and the center section run from front to rear which creates a problem as far as spacing. The front and rear 10'x29' sections will have lights running left to right and the 10'x29' center section would be running front to rear. Won't that create problems in design, spacing and light coverage?

      Jack, I am presently using four 4 tube 8ft. T12's I got used over 20 yrs. ago. Last august I bought 5, four tube, T5's x 4'. I put one up to check if I found them to be too bright, my 67 year old eyes like it so far, I just don't stare at it,. One thing I liked about this particular model was that you can switch the fixture to use 2 or all 4 tubes at a time. I got them at HD if anybody is interested. They are spendy though $90 plus tubes. If you go on the web you can get the tubes for almost half, for 10 or more. (HD) So I was toying with the idea of using those on the rear wall where my work benches are and switching them seperate from the rest of the shop. To save some money, then maybe get the four tube T8's x8' in the rest of the shop that is switched left and right side of the shop, that might be a problem as far as rows/columns. I haven't quite made my mind up on the 4' T5's and the 8' T8's yet as far as the rest of the shop , I do like the switching capability of the 4' T5's though.

      So Jack, if you could share some of your expertise and knowledge, I would be very grateful. John
    1. John Cavette's Avatar
      John Cavette -
      didn't know how to do this but hit reply to the last entry
      sorry
    1. Jack Lindsey's Avatar
      Jack Lindsey -
      Quote Originally Posted by John Cavette View Post
      didn't know how to do this but hit reply to the last entry
      sorry
      Hi John, sorry for the delay in responding. I’ve not been on the forum for a couple of days.
      You’ve raised several questions that I’ll try to answer.

      First, with regard to the orientation of fixtures due to the joist patterns: psychologically most of us favor uniformity in a lighting layout but from a performance standpoint it really won’t make any difference how the fixtures are oriented in the spaces you describe provided they are spaced according to the guidelines I’ve provided in the article. You are correct in suspending the fixtures at or below the bottoms of the joists. You could also consider mounting them to the bottoms of the joists if conditions permit.


      Your T12 fixtures are outdated but there is no reason to scrap them as long as you have T12 lamps. I suggest that when new fixtures are installed you use T8’s rather than T5’s since the high brightness of the smaller diameter lamps can produce objectionable glare.
      As far as being able to switch pairs of lamps independently in 4 lamp fixtures goes, this is a function of the ballasting of lamps, not the lamps themselves. Back in the days of magnetic ballasts each ballast typically drove two lamp so 4 lamp fixtures had two ballasts that could be switched independently. The newer electronic ballasts can be manufactured to drive two or four lamps so for reasons of economy a four lamp fixture typically uses one ballast that drives all four lamps. If you want to be able to switch two lamps independently of the other two you must use two 2 lamp ballasts.

      One last suggestion. You should use fixtures with reflectors since they will not be mounted on a highly reflective ceiling.


      Hope this answers your questions. Let me know if it doesn’t.
    1. Jeff Mazur's Avatar
      Jeff Mazur -
      Not loving the article. Far too much detail about things of limited importance to the task at hand (e.g. I don't need to know how the bulb is constructed - the WHY of color temperature and other important factors in choosing is interesting but extraneous, better left as sidebar info or as a separate link.) The work that went into this is much appreciated, thank you. Better editing would have taken it from good to great.
    1. Neil Persaud's Avatar
      Neil Persaud -
      We are setting up a 10,000 sf shop and this article was extremely helpful.
      One question, does the fixtures in the rows have to be continuous? How do you determine the fixture spacing in the same row? Thanks in advance for your answer.
    1. Jack Lindsey's Avatar
      Jack Lindsey -
      Quote Originally Posted by Neil Persaud View Post
      We are setting up a 10,000 sf shop and this article was extremely helpful.
      One question, does the fixtures in the rows have to be continuous? How do you determine the fixture spacing in the same row? Thanks in advance for your answer.
      No Neil, the fixtures do not need to be mounted in continuous rows. They can and frequently are mounted individually. The explanation is lengthy so if you want to pm me a mailing address I'll send you a copy of an article I wrote that includes diagrams and an example. I discussed continuous row mounting in the Sawmill Creek article since that method usually has lower electrical wiring costs.
    1. Joel Turner's Avatar
      Joel Turner -
      Hi Jack,

      Following on my previous question earlier in the thread and Neil's question on lighting rows being continuous, my space is not a perfect rectangle. You advised me earlier to put 2 rows of 5 two light fixtures in my space. How do you compensate for different room widths? In other words, the first 10 feet of my basement is 15.75 ft wide and then narrows to 13 feet for the remaining 11 feet of length.

      My thought is to just divide the room and half and light accordingly. I'll still have 10 lights. I'll just adjust the wall spacing and row spacing to match the dimensions.

      Does seem reasonable or do you suggest something different?

      Thanks,

      --Joel
    1. Jack Lindsey's Avatar
      Jack Lindsey -
      I'm a little confused, Joel, about the dimensions of your space. In your earlier post (June '14) you described two areas totaling 456 sq ft and now they total 263 sq ft. Is this the same space or do you now have a different area you want to light? If it is new, how high is the ceiling, and what color are the walls and ceiling?
    1. Joel Turner's Avatar
      Joel Turner -
      Quote Originally Posted by Jack Lindsey View Post
      I'm a little confused, Joel, about the dimensions of your space. In your earlier post (June '14) you described two areas totaling 456 sq ft and now they total 263 sq ft. Is this the same space or do you now have a different area you want to light? If it is new, how high is the ceiling, and what color are the walls and ceiling?
      Sorry for my poor description. The space is the same. I have two areas in my basement divided by mechanicals. One is approximately (289 sq ft) and the other 9 ft by 18 ft (167 sq ft). The first area is what I was referring to in my follow up question. The length of that space is approximately 21 ft; however the width differs. If you were to divide that space in two, you would end up with the front of the shop at 11 ft by 13 ft and the rear of the shop at 10 ft x 15.75 ft. If I light the shop in continuous rows, I'm concerned the lights in the rear will cast shadows since they will be too far away from the wall. Of course that's where I'm planning to put my workbench.

      My thought was to light the front of the shop as suggested ( 2 rows of 3 lights ,7.5' apart, and 3' from the walls) and the rear of the shop with 2 rows of 2 lights, about 8' apart, 4' from the walls. Total fixtures remains unchanged from the original recommendation, but the layout is designed to match the dimensions.

    1. Jack Lindsey's Avatar
      Jack Lindsey -
      Joel, I'm having difficulty envisioning what you propose. Can you post a drawing showing the floor plan with the proposed fixture locations and all dimensions? If not I'll pm you my mailing address and you can mail me a drawing. I'd rather be sure I understand what you are proposing before offering an opinion.