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Thread: Fluorescent lights

  1. #1

    Default Fluorescent lights

    Quick question:
    I have heard the fluorescents light will last a lot longer if they are left on with as little on/off cycles as possible Is this so? And if it is, does anyone have any idea how the constant "lights on" effects one's monthly electric bill?
    I have a ton of them in my shop and am mixed as whether or not to leave them running or try to keep the electric bill down
    Thoughts?

  2. #2
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    Default

    If you did a bunch of math, you'd find that it costs about $6 per month to operate one 8 ft tube, at a rate of 10 cents per kwh. That's leaving it on all the time. I've seen those tubes run for more than 5 years before failing, but if we take 5 years as the replacement time, then the cost of running them will be about $360 per tube, plus replacement cost. Let's say they are $10 to replace. So that's $370 over 5 years. Per 8 ft tube.

    Now let's say you switch them on and off many times per day. They'll still last 3 years or more. But let's say they only make it 2 years. Your cost of running them has jumped from $370 to $395 over the 5 year period. But that's if you still have them on for practically all of 24 hours per day. If you ran them for 8 hours per day, and they only lasted 2 years, then your 5 year cost of running and replacing them is then $145. That's assuming a shorter lifetime than I'm used to seeing from them, a replacement cost of $10 per bulb, which is a little higher than I can currently get them for, and an energy cost of 10 cents per kwh.

    Now let's say that after 5 years the ballast had died, and that it's solely because you switched them on and off all the time, like you had nothing better to do. I can buy a ballast for about $40, so that represents $20 per tube, and if you add that to the cost of running the lights 8 hours per day, it still only costs $165 to run one tube for 5 years.

    So you leave them run all the time and it costs about $400 per five years per tube, and if you switch them on and off all the time, but don't leave them run all night, it's about $160 per five years.

    The one reason I wouldn't always be turning them on and off is because if it's cold, they won't give a proper light right away.

  3. #3
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    Default

    Not exactly on topic, but strangely, I have lost more ballasts than tubes in my shop in the last 6 years.

  4. #4
    Join Date
    Sep 2004
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    Smile Weird Tubes

    I have a high efficiency sign type tube system in my shop same tubes like 12 years? What am i doing wrong?

  5. #5
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    I believe this "myth" comes from some office buildings where the lights are changed by union help. They probably need to have them on for at least 14 or 16 hours a day anyway so the savings in electricity is not as much.

    I have seen those same buildings use electric heaters in the AC ducts to control the temperature in each area. The AC ran full blast 24/7 and the heaters reheated the air to a more comfortable temperature. 1950s thinking. I doubt that very many such buildings still do that. Likewise for leaving the lights on 24/7.

    As my father often said, "Turn the lights off".
    Paul A.

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  6. #6
    Join Date
    Mar 2005
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    Default Turn the lights off....

    Paul;
    I couldn't agree more, Paul. A simple energy concervation means, yet it is dependent on trained, thinking people.
    On the other hand, building owners/ tennants will spend big bucks to have "energy management systems" installed to turn lights & heat on & off automaticly....(good money to be made in energy consulting...)

    As for heating & cooling, In many large buildings the lighting, equipment load (think maybe data centre, fashion store etc.) and tennant mix may be such that cooling is needed most, if not all, year round. Especially in a temperate climate. Some areas like office/ reception areas may need supplemental heat when the bulk of the load is for cooling. The cheapest way to do this is often with a duct heater...Duct or pipe revisions etc. are expensive and add to tennat improvement costs.

    I agree that it would be better to have seperate heating units, zone control or some such affair but these are usually more expensive to install...

    That's what I've experienced, anyway.
    Rick

  7. #7
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    Default

    Many large office buildings were designed with the lighting system as part of the heating system. For that reason they were left on 24/7 when needed. This design practice has been changed as the "optics" were terrible as it looked as though they were wasting energy. That wasn't the case since any electric appliance converts the electricity it consumes to heat with 100% efficiency.

    BTW, using lighting for heating gives excellent zone control (when the offices aren't in use).
    Last edited by Evan; 12-01-2006 at 09:23 AM.
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  8. #8
    Join Date
    Apr 2004
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    You didn't specify what voltage, lamps and ballasts your currently using, but our customers are looking at changing to T5 lamps and electronic ballast as a cost savings over the older T12 and wound ballasts. This may be something you may want to look at if you have a large number of fixtues. There's alot of factors to consider depending on your aplication. Ceiling height, avalible voltage, and amount of lumins required are just some of them. You may want to contact a local electrical contractor to do the the math for you. As a rule, they will do this at little or no cost in the hopes of getting the fixture change out job. After you've decided which way you want to go, write up an outline specification and put the job out for bid.

  9. #9
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    No one has addressed the issue of the initial surge to the ballast when first turning the fluorescent lights on. I was taught that you were wasting money if you needed to turn them back on within an hour, but have heard others say that it wasn't an issue.

    Then there is the wear and tear on the switches and switch plates.

    Ross

  10. #10
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    Fluorescent lamps are rated in part by the number of starts they undergo. You generally won't find that rating stated anywhere but too many starts will kill them before they otherwise wear out. Usually, the faster the lamp starts the more the starts wear it out because of the very high starting voltage applied, as high as >400 volts.

    Another thing to consider is that some fluorescents have really poor power factors, around .5 or so. If you are being charged for poor power factor you need to figure that in the calculation. If you have a lot of fluorescents it is a good idea to check the power factor of the ballasts.
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