Shop Lighting

[Micheal Roth]

I ran two runs of 24 feet of the lower output T8's for most of the time working out there because they are less expensive to run. I also have one run of 24 feet of HO lights down the middle for when I am doing something like final sanding or staining or spraying finish where I really need a lot of good color light. The two runs of T8's are on one switch and the HO's are on another one so I can turn them on separately. My shop has 9 1/2 foot ceilings and is 24x32 total. Probably a little overkill but I don't regret it a bit.

I will say the HO's do hum a little though. I like the function of the electronic ballast T8's better.

I'm going to use 2 runs of 32' low output T-8's 4' in from the outside walls and 1 row of 24' lower output t-8's down the middle. This will give a light spacing of 8'. This should give me plenty of light.

[Rick Prosser]

Is there a chart, or software that can help layout the lighting for the shop? I will have a 40x70 room with 14 ft walls to light. Not sure if I need to drop the lighting down to 10-12 ft, or keep them up out of the way. My eyes need a lot of light to see clearly, so I will lean toward overkill.

[Bill Arnold]

I don't know about a chart or other type of planner. I used practical experience with various shop light fixtures to decide how to light my shop. The attached image shows the arrangement in my shop. All of the fixtures are recessed in joists to maintain clearance and protect them somewhat.

The old section (left) has eight four-foot, two-bulb T8 fixtures. They are on two switches; one bank is shown in red, the other in blue. The addition I built (right) has 12 of the same type of fixtures. Again, I have them on two switches; one bank in red, the other in blue.

I rarely need additional task lighting but have some available for the bandsaw and lathe, if needed.

(Joists are 16" OC in the old section since they double as floor joists for the loft; the new section is 24" OC)

[Eric Gustafson]

A word of warning: don’t judge the color of a lamp by color temperature alone. There is another metric, color rendering index, which must also be considered. I’m not going into a discussion of CRI unless someone is interested.

I was searching for posts on fluorescent lights and found yours. You did such a great job on color temp, can you explain CRI, too?

[Leo Graywacz]

In simple terms it is color accuracy compared to sunlight at noon. The sun has a CRI rating of 100. The closer to 100 your lamp is the closer to true sunlight it is. Good is in the upper 60's and very good is higher that 92. I have seen a few around 95 but it starts to get expensive.

[Jack Lindsey]

I was searching for posts on fluorescent lights and found yours. You did such a great job on color temp, can you explain CRI, too?

Color rendering index describes the correlation between the spectral distribution of a light source and the spectral distribution of a blackbody radiator operating at the same color temperature. In plain language it means we measure how much light of each color is emitted by the light source compared to how much is emitted by our iron ball. The higher the number, the more closely the light source will match the way we see colors lighted by the iron ball.

As far as predicting how well colors will be rendered the metric by itself is meaningless. Why? Because at low temperatures the colors of light emitted by the ball are primarily in the red region and blues, greens and other colors won't be rendered well. By the same token the color will shift to the blue region at high tempertaures so cool colors - blue and green - will look good but warmer reds and oranges will be muted.

For example, the sun is a perfect radiator, actually better than the iron ball, and has a CRI of 100. It also goes through a wide range of color temperatures over the period of a day. At dawn it is about 800K, around 10,000K at noon on a bright summer day, and back to 800K at dusk. Are colors rendered equally at dawn, 10AM, and noon? Not even close!

Incandescent lamps are very close to the sun in terms of spectral distribution within the visible portion of the spectrum and also have a cri of 100.

In order to predict how well a light source will render colors we must know both the color temperature and CRI. In general higher cri's will render better colors but understand that lower temps will be better for reds and higher temps will be better for blues.

Now the disclaimer - this is a highly technical topic and the above explanation is greatly simplified. It is not a scientific explanation but does cover the concept. For a more deyailed explanation see the IES Lightig Handbook, or my book, Applied Illumination Engineering (Fairmont Press/Prentis Hall)

[Mike Cruz]

I put the T8 6' long 2 bulb versions from HD in my shop. The shop is 24 x 30. Each rafter has 2 fixtures along its 24' span. Rafters are 4' apart. There are 7 exposed rafters (9 total, one on each Gable end). So that would make 14 lights. That is in only in theory. Because of a finishing room and wood rack that combined take up 1/4 of the floor plan, I ended up with 11 lights.

In the section that is 24 x 15 (approx) there are 4 exposed rafters with 2 fixtures on each rafter along the 24' span. This accounts for 8 of the fixtures. I have these 8 on 2 seperate circuits (alternating rafters). So I can light up that entire area with either one of those two circuits (4 lights on 2 rafters that are 8 feet apart) or with both circuits (8 lights on 4 rafters that are all 4 feet apart).

In the section that is 12 x 15 (approx) there are 3 exposed rafters with 1 fixture on each rafter along the 12' span. This accounts for 3 of the fixtures. I have these 3 on 1 circuit.

Lights up the shop very well. Hope that wasn't as confusing as it may have sounded.

[glenn bradley]

Ya gotta love having a guy like Jack around who is so giving of his time and info. I run 15, 2-lamp, T-8 fixtures in a 20 x 30 shop. Lamps are 6500k with a CRI in the low 90's. I have an unfinished ceiling at about 9' and the fixtures hang on very short chains. I have two walls finished in semi gloss white and one flat white (it was already that way) and one really messed up wall that is mostly covered with lumber rack, cabinets and other hanging fixtures.

The light distribution and coloring is working well for me. I have no eye fatigue after long hours like I used to get with the few original shop lights and the shadowy areas that came with them. I do use lights of a known type when color selecting for an environment. This usually means going to a room in the house and setting lights up as no one I know puts my furniture in lighting like I have in the shop ;-))

[Eric Gustafson]

Thanks for the reply, Jack. You did a great job "illuminating" what can be a confusing topic for the layman.

[Jack Lindsey]

Thanks, Eric and Glenn, for your comments.