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Thread: Lighting design questions - T5 and T8 fixtures

  1. #1

    Lighting design questions - T5 and T8 fixtures

    I'm new to lighting design, including T5 and T8. I've always just hung cheap T12 shop lights where I needed them. Time for a change, and I need to get educated.
    I'm considering using 24x24 suspended ceiling T5 fluorescent fixtures and surface mount them to the ceiling of my shop after enclosing the two open sides with painted sheet metal. Finished height will be 6".

    The T5 fixtures I'm looking at have two parabolic reflectors, two electronic ballasts (B228PUNV-C) and holds one, two, or three F24T5 HO bulbs in the center of the fixture. Bulbs are included, temp is 3500K, 2000 lumens per bulb. Spacing criterion is 1.3 x heigth perpindicular to the axis of the reflector and 1.2 x heigth parallel to the axis. Ten foot ceiling in my shop.

    I can get these 24" T5 fixtures for a price comparable to the price HD and Lowes ask for surface mount 48" T8 fixtures.

    The prevailing opinion I've found on the forum indicates that T5 is both too bright and too expensive, most folks go with T8.

    For the same inital money per fixture would you go with F24T5 or F48T8 fixtures?
    Do I need more 24" fixtures than would be required for a 48" fixture installation, considering a brighter 24" fixture?
    Do I need to calculate spacing based on ceiling to floor heigth or ceiling to workbench heigth?
    These fixtures have a 73% efficency rating - is this good, lousy, or what?
    Will enclosing the open sides of these fixtures and using them as surface mount fixtures cause any temperature related problems?
    Thanks,
    Glenn

  2. #2
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    I wouldn't use the 2' lights - go with the 4'. Seems to me that the 4' bulbs will be cheaper in the long run.

    I've got no opinion on the Kelvin rating.

  3. #3
    A T-8 (mine, at 5000oK) produces 1800 lumens perbulb. A T-5 is the bulb of the future. It is more efficient (lumen per watt)and bulbs will continue to fall in price over time. 5000oK bulbsessentially replicate daylight – and are the only way that I would go. Thedifference is amazing. T-5’s start much better at cold temperatures than T-8’swill. The other component that makes a big difference between fixtures is thereflectivity of the reflector surface. Polished aluminum probably offers thebest bang for the buck. With a new install, my recommendation would be T-5’s at5,000oK with high efficiency reflectors & same number of fixtures as you would use with T-8's. If you want to think aheada few years, make certain that your ballasts are dimmable as well. http://www.lrc.rpi.edu/programs/NLPIP/lightingAnswers/LAT5/pc5.aspRead install directions for information on surface mount. I'm in a non-code area but heat output from electronic ballasts is a lot lower than old technology. If you worry a lot, use a pair of spacer blocks on each fixture. If you look at a T-5 fisture with two bulbs at 2000 lumens per bulb spread over 4 sq ft (1000 lumens per square foot); and T-8 fixture with two bulbs at 1800 lumens per bulb spread over 8 square feet (450 lumens per square foot), your eyes can easily see the difference. The 400 lumen difference between the two bulbs can't be seen by a typical human - but the difference in lumens per square foot can be easily discerned by a human. It is lumens at the surface which is important.

  4. #4
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    Wow, that's a lot of technical questions that I'm not really qualified to answer. But I also believe that you may be over thinking this whole thing.

    I just recently installed T8 lighting in my shop and struggled with a few of the same questions. I have an L-shaped layout that equals about 600 sqft. Just twelve 4' double bulb fixtures (spaced 3 feet apart) fixed my lighting problem quite nicely. Of course, they have no reflectors (due to the fact that I ran conduit to them), so they're a little brighter than usual.

    Basically it boiled down to this:
    (a) Measure your total square footage.
    (b) Figure out the lumen-ratio from fixture to workbench top.
    (c) Add cost of wiring and other installation materials.

    The reason most people use 4' or 8' long fixtures is because they cover more area and they're easier to find replacement bulbs for... at least that's why I used them... your mileage may vary.

  5. #5
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    There was an article in the February 2002 FWW IIRC written by a fellow Creeker about designing shop lighting. The guys name escapes me now and if I remember correctly, he's a retired lighting engineer. In the article he explains how much light is desireable based on age. IIRC....over age 40 you need twice as much lighting per square foot. He explains how to calculate base on square footage and distance between light height and working surface height. I used 8' fixtures that contain 4 - 4' T-8 bulbs. I used his article to design the number and positioning of the fixtures. There are no shadows in my shop and everybody compliments me on the lighting there. In the article, he explains how to recognize the quality of the ballast and what ballast ratings mean. The ones I bought weren't the cheapest ones at HD but in 6 years I haven't had a single failure of ballasts and only a couple lamps have gone bad.

    '
    Last edited by Ken Fitzgerald; 02-05-2012 at 11:34 PM.
    Ken

    So much to learn, so little time.....

  6. #6
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    I asked my local auto parts guy about the T5 and that is what he uses in his store and he said that he does not remember replacing them in the addition he added several years ago. When I get or build a different shop that is what I am going to use. I actually thought about outfitting my garage shop with them but figured we are not going to be in this house for very much longer and decided to hold off. I would go with the T5, I have some 4' T8's in my garage and it seems I am always replacing them. Ultimately the choice is yours and my thoughts are free. Good luck on what you decide.

  7. #7
    FWIW, new governmental standards for lumens per watt means that certain T-12 & T-8 bulbs will no longer be produced. This began this year and will continue to expand with more bulbs being phased out over the next two years. I`m going to just stock up on replacements.

  8. #8
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    We installed about 3 dozen T-5 fixtures in a factory area three years ago. The run eight to ten hours per day. We have yet to replace a bulb. We did have two fixtures go bad shortly after they were installed that were replaced under warranty. They are very bright, at first some workers complained about how bright it was, but they soon learned they no longer needed their task lights and could see their work. Our local lighting distributor did an illumination plan for free that showed us the desired layout for fixtures to achieve our target illumination level.
    Lee Schierer
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  9. #9
    Miscellaneous thoughts:

    I've been to office supply auctions and dealers and seen hundreds of fluorescent fixtures that could be had for a buck or two.

    For me, daylight balance is far preferable. I put some in and asked the little woman what she thought and she just shrugged her shoulders.

    If you have fixtures, it might be worth it to install an electronic ballast in one as an experiment. As far as I know, a new T-5 is just a narrower bulb with an electronic ballast. I could be wrong! I know I have a fixture that uses narrow fluorescent bulbs that predates electronic strobe lights.

  10. #10
    If you're looking for bang for your buck 4' T8's are the way to go over 2' t 5's. I don't know if you've priced the lamps, but the difference is huge. T8's are far from being legislated out of existence, there are 700 series lamps that will go away, but the 800 series lamps ( basically color rendition and efficiency differences) will be around for a long time. If you're concerned about efficiency, a standard T8 is a 32 watt lamp, they are also available in a 28 and 25 watt lamp, but of course at a cost. T5's have been around for a while now, and offices, commercial spaces and warehouses etc. are still designed with T8 fixtures based on cost effectiveness. Lithonia Lighting offers a simple lighting layout software that you can download, that allows you to plug a fixture type into a 3 dimensional space, input your footcandle requirements and it will give you quantities and spacing for the fixture. The software is called Visual. T8 fluorescents are far from being an obsolete technology, I'd spend my money elsewhere.

  11. #11
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    Jack Lindsey. Great article. Lots of good information, but probably needs to be updated with the new offerings. Jim.
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  12. #12
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    I recently installed 8' T5s with electronic ballasts from the borg. I couldn't be happier. My shop gets pretty cold for TX, but they have not failed to start once. The ones my local HD sells do no have a reflector. I have a 4' T8 in the back of my shop and even with the reflector it has on it, it is not even close to as bright as the T5s. Night and day difference. The 8' at HD run ~$70 each in my area.

  13. #13
    FWIW, I recently purchased Lowes SKU #163725 fixtures , T-8 8 ft High Output (110 watt) with 0 degree start capability. $56.55 each. Bulbs are SKU# 327859 @ 6.99 each
    Fixture quality is so-so but the light output is quite good. 4 fixtures seem to provide enough light for a 20' x 24' space. May add 2 more as shop build continues and equipment moves in.
    Then again, my eyesight is terrible ( 800 over 20) and I`m over fifty. YMMV
    Last edited by Randy Rose; 02-07-2012 at 5:55 PM.

  14. #14
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    T5s are 5/8" diameter and T8s are 1" diameter. I thought I read somewhere that T5s are also shorter than T8s? A 4' T5 fixture uses 44" bulbs? If this is true and they phase out T8s, retrofits could be expensive, or a lot of trouble. T8s are the same length as the conventional T12s. The T12s are 1-1/2" diameter. I put 4' T8s from HD in my shop. The fixture and ballasts were about $30. I haven't had any trouble with them.

    Mike

  15. #15
    While 5000K is better than 2000K or 3000K, it is still pretty yellow. I would shoot for a minimum of 6500K, which is the color temp of sunlight at noon. You should notice a difference between 5000K and 6500K pretty easily.


    Kim

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