heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) (05/12/91)
The question recently came up here of the minimum duration of absence from a room (an office in this case) that justifies turning off the fluorescent lighting. I turn them off whenever I'm going to be gone for more than two or three minutes. One fellow said he had heard that you should leave them on unless you'd be gone for more than forty-five minutes. Is there someone out there who can provide a firm answer to the question?
wayned@wddami.spoami.com (Wayne Diener) (05/12/91)
In article <HESKETT.91May11123526@polymnia.titan.tsd.arlut.utexas.edu> heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) writes: >The question recently came up here of the minimum duration of absence >from a room (an office in this case) that justifies turning off the >fluorescent lighting. I turn them off whenever I'm going to be gone >for more than two or three minutes. One fellow said he had heard that >you should leave them on unless you'd be gone for more than forty-five >minutes. Is there someone out there who can provide a firm answer to >the question? During the winter, I don't bother to turn my lights out unless the actual light is bothering me ... my house is electrically heated ... the electric power "wasted" by the lights simply helps to heat my house ... same price as what goes into the furnace. Also helps reduce wear & tear on switches, ballasts, etc. During the hot summer months, you pay significantly more than twice as much for that waste heat, at least if you have air conditioning. Then, the "wasted" electric power heats my home and requires additional electricity to remove the heat. I think the answer is pretty dependent on the type of building, geographic location and time of year, etc. -- |---------------------------------------------------------------| | // Wayne D. Diener | | // Spokane, WA | | \\ // E-mail reply to: | | \X/ To: isc-br!hawk!wddami!wayned@uunet.uu.net | |---------------------------------------------------------------|
walvdrk_r@pttrnl.nl (05/19/91)
In article <HESKETT.91May11123526@polymnia.titan.tsd.arlut.utexas.edu>, heskett@titan.tsd.arlut.utexas.edu (Donald Heskett) writes: > The question recently came up here of the minimum duration of absence > from a room (an office in this case) that justifies turning off the > fluorescent lighting. I turn them off whenever I'm going to be gone > for more than two or three minutes. One fellow said he had heard that > you should leave them on unless you'd be gone for more than forty-five > minutes. Is there someone out there who can provide a firm answer to > the question? If you'd like to conserve power, it's worth while turning off the lights for a few minutes. But ... the tubes have a very long lifetime. Only the heated wires at both ends of the tube haven't. These wires are only heated during the start-up of the tube and that's when they suffer more than during the normal "burning" operation of the tube. However, I don't know how many start-ups a standard tube is supposed to last, but suppose it is 5000 times. Lifetime of the tube itself is something like 10000h. So if, on the average, the on-time is longer than 2h, the tube will end it's life because of the tube, rather than because of the heated wires. So it's -without any doubts- defendable to switch of the tubes for a short time as long as the average on-time stays at 2h or more. If the average on-time is shorter, the tube will end it's life because the heated wires are worn out. Your energy saving has to account for the premature replacement of the tube. Worst case: the price of a new tube. Suppose the price is $5.00 and the kWh price is $0.10 a new tube equivalents 50*(1000/32) hours of on-time (for a 32W tube). So, if you save more than 1563h on-time during the life time of a tube, it's certainly more economical to switch it off. In normal circumstances you've only to make up for the price difference, so it's already more economical to switch the light off with less than the (worst case) 1563h of saved on-time. So I guess, you'll have to split the lighting of your office in 2 parts, connect kWh meters to both halves and set up an administration of when your tubes have to be replaced. Switch one half with one strategy and the other half with the alternative and after a number of years ... ;-) -- Kees van der Wal e-mail: JC_vdWal@pttrnl.nl ---------------------------------------------------------------------------- PTT Research Neher Laboratories P.O. Box 421 2260 AK Leidschendam The Netherlands Phone: +31 70 3326295
dag@hp-lsd.COS.HP.COM (David Geiser) (05/22/91)
I just bought some tubes and noticed that the manufacture had rated their life at 10,000 hours with a ten hour derating for every on/off cycle. dag
john@zygot.ati.com (John Higdon) (05/23/91)
In article <1991May19.164508.65064@pttrnl.nl> walvdrk_r@pttrnl.nl writes: >But ... the tubes have a very long lifetime. Only the heated wires at both ends >of the tube haven't. These wires are only heated during the start-up of the >tube and that's when they suffer more than during the normal "burning" >operation of the tube. However, I don't know how many start-ups a standard tube >is supposed to last, but suppose it is 5000 times. There are three basic starting types each representing a distinct trauma to the tube (or starter). The oldest type uses a bi-metal starter which is in series with the filaments of the tube. When power is applied, an inert gas (such as neon) conducts in the starter, heating the bi-metal strip. When the strip heats, it completes a circuit through the tube filaments which then heat up. Meanwhile the strip is cooling since its closure stopped the conduction through the neon gas. When it opens once again, voltage is once again available at the ends of the tube and since the filaments are hot, the tube conducts and lights. Sometimes several tries are necessary and this is why lamps of this type flicker when starting. What usually fails first in this system is the little capacitor across the bi-metal strip. This cap suppresses noise and helps with the inductive kick from the ballast to start the lamp. When this cap shorts, the lamp sits there and glows orange at the ends. A nicer method of starting flourescent lamps is "rapid start". A special ballast is used which applies current to the lamp's filaments at the same time it applies a high voltage across the tube's length. The high voltage causes the tube to conduct almost instantly, and as the filaments heat the tube draws more and more current, lowering the voltage across it. The tube smoothly comes up to operating current within a second or so. This is the least destructive way to start a flourescent lamp, but since current is applied to the filaments constantly, it is not the most efficient. It is very popular, however. The third way is called "instant start". This is the almost-universal method used in the longest tube lengths. No current is sent through the filaments. In fact, these tubes only have one pin at each end. The ballast sends a very high voltage through the tube, causing it to conduct instantly (as a cold-cathode lamp). Very quickly, the filaments heat from the current flowing through them as cathode/anode. (They switch roles sixty times a second.) When they heat, the tube switches from a cold cathode lamp to a hot cathode lamp, and the ballast allows the voltages and currents to change accordingly. There is some filament wear during the cold-cathode phase of operation, as well as during the transition to hot-cathode state. Starter-type lamps should be turned on and off as little as possible. Rapid start lamps can be turned off whenever desired. Instant start lamps fall somewhere in between. -- John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !