Can I have too much fluorescent lighting?

[Peter Rawlings]

This tool may prove useful for those contemplating lighting scenarios.

http://www.visual-3d.com/Software/In...l/Default.aspx

Download the program, go to the Photometric Profiles and find a similar device to what you're considering. Plug in dimensions and characteristics of your space and it will give a prospective layout and lumens per sq. ft. throughout the space.

Took some playing around with it to get familiar with it all, but not a mind blower.

Ended up shooting for around 50 lumens per sq. ft. total, in two stages. The first stage is really good, the second is killer lighting and it's all very even.

My biggest question was knowing what the target should be. I actually went to a former employer and calculated what the light was in a particlarly well lit addition, so I had a known basis.

Attached is a sample of result.

[Jack Lindsey]

Peter, Greg stated that his shop is 20 x 20 but your drawing implies different shape and thus different measurements. You also show a layout using 15 fixtures

What shop size did you assume?

What are the components of the assumes 0.63 light loss factor?

Where did you get the 50 footcandle lighting level?

[John Keeton]

One strange phenomena I have noticed is that as my hair gets lighter and thinner, my shop gets darker! I am sure it is just the bulbs aging, and not me

[Peter Rawlings]

Peter, Greg stated that his shop is 20 x 20 but your drawing implies different shape and thus different measurements. You also show a layout using 15 fixtures

What shop size did you assume?

What are the components of the assumes 0.63 light loss factor?

Where did you get the 50 footcandle lighting level?

Forgive me if this in not the proper way to post directly to a query, this forum format is unfamiliar.

I didn't model any particular space, although I'd be happy to. It was intended as an example of what the software does. The model is 30 x 50.

As to the components of light loss calc;There are several ready made sets of parameters available in the program, I simply chose a description that seemed most appropiate. As to the actual specifics of said parameters, it may be there, I never investigated.

The lighting level seemed to me the most slippery of subjects. Many opinions out there, lots of by guess and by golly. I read much on forums and mfgs. websites. I arrived at the 50 level in the way I described coupled with info gleaned elsewhere. If anything I wanted to err on the side of too much, these eyes getting no younger. I also added receps in the ceiling for possible task lighting later on. In truth I don't know if I'll ever use it, but it seemed like a good safety valve.

From what I recall, 15 to 30 fc is adequate lighting for many things, 75 to 100 for really critical need such as surgery or other precision work. I also had worked where there was a good and not-so-good lighting within the same buiding, so I did have basis to start from...a nice place to start.

I'm no expert, but I did try to quantify data to make an informed choice. I really don't like looking back and thinking, if only...

There is an curious phenomenon I've observed. Even though I staged the lighting 50/50, to my eye the first stage seems to illuminate greater than 50%. A WAG would be 75%. This could be perceptual or have to do with reflectance or who-knows-what. It's interesting to me, but mostly I wanted great lighting, not a deep understanding of theory.

[glenn bradley]

The difference is so significant that the remaining T-12's will probably go first chance I get.

It was like a prophecy. I just used a coupon from Lowe's to pick up 3 more fixtures at about $15 each.

[Peter Rawlings]

Since someone asked, I modeled your shop space and proposed lighting and here's the result. It looks like plenty of light from my limited experience, but I doubt you'll regret it. Perhaps staging would be prudent. What I've found is that I use the 2nd stage only some of the time.

What I really can't say is what the perceptual and practical difference between, say 50fc per sq.ft. and 75fc. Like I said earlier, difinitive info is hard to find and varies with the person and their experiences, it seems.

I should also add that in my situation, there's a fair amount of light from windows, a detail I changed from original plans.

[Jack Lindsey]

Thanks for posting the revised layout, Peter. That looks a lot more realistic.

The light loss factor is the product of ballast factor, lamp lumen depreciation factor, and luminaire dirt depreciation factor. There are other factors that are sometimes considered but these are the ones I think will apply. Based on the input watts and calculated footcandle levels I assume that the ballast factor is probably fairly low - in the .70 plus or minus a little- range.

Your proposed layout should be fine for someone Greg's age. For age 40 and up I'd recommend using a higher ballast factor.

One suggestion. The layout shows an end to end separation between the fixtures. It's a lot easier to install them butted together. That way the fixture becomes an electrical raceway so you only nee to feed one fixture in each row. Cuts down on wiring cost, especially if you hire an electrician.

[Peter Rawlings]

Thanks for posting the revised layout, Peter. That looks a lot more realistic.

The light loss factor is the product of ballast factor, lamp lumen depreciation factor, and luminaire dirt depreciation factor. There are other factors that are sometimes considered but these are the ones I think will apply. Based on the input watts and calculated footcandle levels I assume that the ballast factor is probably fairly low - in the .70 plus or minus a little- range.

Your proposed layout should be fine for someone Greg's age. For age 40 and up I'd recommend using a higher ballast factor.

One suggestion. The layout shows an end to end separation between the fixtures. It's a lot easier to install them butted together. That way the fixture becomes an electrical raceway so you only nee to feed one fixture in each row. Cuts down on wiring cost, especially if you hire an electrician.

Jack, I see reference here of an article you wrote, is that correct? Where might I read it?

I admit to being curious about all this, there's more to it than I ever imagined. My shop's already done, with a target fc averaging 52 or so (according to the Visual model)...and I'm 53! It would seem you're advocating substantially more than that and I'm having a hard time imgining more light being needed, but it's all new, so that may change in time.

Does the lumens output or any given lumiaire diminish much over time? Can you elaborate on balast factor, I'm unfamiliar with the term.

What's your take on my observation as to percieved light level changing less as lumens climb? To put another way, it seems to me that my first stage illuminates more than 50%. When the second stage is turned on, it just doesn't seem twice as bright, but that's purely subjective.

Appreciate your input.

[Ken Fitzgerald]

Peter...IIRC Jack's article was in February 2002 Fine WoodWorking. Excellent article. I used it to design and install the lighting in my shop and haven't been disappointed!

[Edward Henderson]

I have taken a slightly different approach to lighting in my 24x24 garage shop. When I built the garage 25yrs ago I had no idea that I would be out in the garage as much as I am now so the provision for lights was minimal. When I did decide to augment the lighting I did it piecemeal, bit by bit. I have since had to modify most of it.
I have a problem with the flourescent lights in my shop probably because I was working with a tight budget and opted for the cheapest fixtures I could find, including castoff's from work. My fixtures drip a black goo occasionally.
So I have replaced a few of the fixtures that are over work area's with incandecant fixtures, some with the new flourescent bulbs. Where possible I have put them on separate pull switches so they can be off when I'm not working there. Over my tablesaw, router table and scms I have installed spot lights that highlight the blade area. I like the spots because they aid with accuracy and remind me of the danger. I also have a scms permamently mounted on a portable fold up stand and have attached small led lights to light both sides of the blade.
My vision is pretty good for an old guy but I find that task lighting is very helpful and urge anyone just setting up shop to consider it.

[Jack Lindsey]

Ken, we've chatted before. Glad to learn that you are still pleased with your lighting.

Peter, Ken posted the info on the article I wrote for FWW. If you really want more info you might try to find a copy of my book "Applied Illumination Engineering", Second Edition. It's out of print and the lamp chapters haven't been updated to include the latest technology but everything else applies.

To answer your questions:

Ballast Factor - when a lamp manufacturer tests a lamp to determine light output they operate it on a special current limiting transformer called a "reference ballast". These devices are large, heavy, and maintain excellent waveform to drive the lamp. The lumens produced by the lamp on this ballast are the rated lumens published in the lamp manufacturers catalog and on the lamp packaging.

Ballasts used in commercial fixtures are smaller, lighter, and don't provide ideal current characteristics for the lamp so they drive the lamp at a light output somewhat lower than the reference ballast. This also applies to electronic ballasts, especially with reference to waveform. The percentage of rated lumens that the ballast causes the lamp to produce is called “ballast factor”. If a lamp is rated at 3000 lumens but produces 2820 lumens when operated on the commercial ballast the ballast factor will be 2820/3000 = 0.94. A high quality magnetic ballast can be expected to drive a lamp at about 85 % for energy saving lamps, and 95% for full wattage lamps. Electronic ballasts vary over a wide range from about 70% to over 110%. A low ballast factor isn’t necessarily a bad thing since wattage is also reduced. The important thing is to know what the ballast factor is and adjust your calculations accordingly.

As fluorescent lamps age the gradually drop off in light output. The phosphors, the white powder that coats the inside of the glass tube, are the light producing element of the lamp. As they age the gradually lose efficiency so light output decreases. Additionally, material evaporates from the cathodes, the wires at each end of the lamp that serve as terminals for the arc, and coats the inside of the tube further reducing light output. The magnitude of the loss depends on the phosphor type and the current loading of the lamp.

Other light loss factors include the build up of dirt on fixture and room surfaces. Fluorescent lamp performance is also effected by the ambient temperature in which they are operated. Most lamps are designed for a still air ambient temperature of 100 degrees F. They may lose some light output in enclosed fixtures which trap heat and raise ambient temps, or if operated in a cold environment.

If your system is fairly new and the lighting levels are close to your design level as you indicated then your system is under designed and you can expect a significant loss of light as the system ages. The loss can be recovered by relamping and cleaning fixtures.

Hope this answers your questions.