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Old 10-24-2008, 06:01 AM   #1
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How much electricity does a fluoresecnt use?


Hi;
I am curious to find a conversion factor in determining how much actual electric power my fluorescent lamps use.
The ones I buy to replace incandescent clearly state how much electricity they use, but what about the tubular "standard" fluorescents.
I am using fixtures that have two 40W bulbs each. They have electronic starters.

Thanks

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Old 10-24-2008, 06:18 AM   #2
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How much electricity does a fluoresecnt use?


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Originally Posted by KE2KB View Post
Hi;
I am curious to find a conversion factor in determining how much actual electric power my fluorescent lamps use.
The ones I buy to replace incandescent clearly state how much electricity they use, but what about the tubular "standard" fluorescents.
I am using fixtures that have two 40W bulbs each. They have electronic starters.

Thanks
Look at the ballast for that number. A 2 lamp, f40, magnetic ballast can pull about 1.2-1.4 amps.

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Old 10-24-2008, 11:32 PM   #3
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How much electricity does a fluoresecnt use?


If you're looking for watts used, a rough figure would be to add the lamp wattages, and times by 1.2

For example, a fixture with two 40 watt lamps would be 40 X 2 = 80 X 1.2 = 96 total watts used.

This is not exact, but pretty close most of the time.

If you're looking for amps, you'll need to look at the ballast.

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Old 10-25-2008, 02:13 PM   #4
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How much electricity does a fluoresecnt use?


I guess I'm confusing myself by comparing the screw-in compact fluorescents with the tubular ones.
The screw-in are say, 13 Watts, and state they give as much light as a 60 Watt incandescent bulb.

So the 4 foot 40W bulbs are really 40 Watts of power, providing whatever in the way of illimination.
I should really be looking at lumens.

The whole question came up because I just replaced a very old fluorescent fixture in the basement. It was two 2ft 20W bulbs, which used starters.
I replaced it with a fixture that has two 4ft 40W bulbs.
We have been leaving it on most of the day, because it's dark in the basement without the light, so I was trying to figure out whether we should be leaving it on all day, or turning it on and off as required.
Problem is, people are going up and down, and the on/off cycle might be too short to make that more efficient than just leaving it on all day.
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Old 10-25-2008, 02:46 PM   #5
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How much electricity does a fluoresecnt use?


If you're worried about power consumption, you could put it on a motion sensor and set the off delay time to like 5 mins. So when there is no one down there it would shut off in 5 mins preventing it from being on all day long.

Edit: Our stair way lights were being left on all the time with a 3 way switch at the top and bottom of the stairs, we'd forget to turn them off or whatever and they'd be on for quite a while. I have since pulled out the 2 3-ways, and wired in two single pole motion sensors. I know you say "two single pole?" It works out great, either one will turn the lights on, but they both have to be off for the light to turn off; the delay is set so short that sometimes it can be a nuisance when you are in the basement and kinda in front of the motion sensor at the bottom of the stairs (they turn on and off frequently). So the one at the bottom of the stairs usually stays in the off position.

Last edited by theatretch85; 10-25-2008 at 02:50 PM.
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Old 10-25-2008, 05:56 PM   #6
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How much electricity does a fluoresecnt use?


Maybe you could benefit from an occupancy sensor?
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Old 10-25-2008, 06:01 PM   #7
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How much electricity does a fluoresecnt use?


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Originally Posted by KE2KB View Post
Problem is, people are going up and down, and the on/off cycle might be too short to make that more efficient than just leaving it on all day.
You are getting too far into this. Simply turn them off when not being used and turn them on when needed. If you want to calculate start up currents and everything, you will go nuts. The additional current for start up will be quite minimal so unless you are simply standing there flipping them on and off, you will benefit from turning them off when not being used.
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Old 10-25-2008, 07:04 PM   #8
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How much electricity does a fluoresecnt use?


I personally would be more worried about a fluorescent breaking in my house and where all the Mercury is ending up in landfills then a little energy saved.
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Old 10-26-2008, 09:46 AM   #9
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How much electricity does a fluoresecnt use?


Not trying to diminish the seriousness of mercury but I have actually played with mercury when I was a kid. I like to think I am ok. this is from wiki:

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Elemental mercury
Quicksilver (liquid metallic mercury) is poorly absorbed by ingestion and skin contact. It is hazardous due to its potential to release mercury vapour. Animal data indicate that less than 0.01% of ingested mercury is absorbed through the intact gastrointestinal tract; though it may not be true for individuals suffering from ileus. Cases of systemic toxicity from accidental swallowing are rare, and attempted suicide via intravenous injection does not appear to result in systemic toxicity.[11] Though not studied quantitatively, the physical properties of liquid elemental mercury limit its absorption through intact skin and in light of its very low absorption rate from the gastrointestinal tract, skin absorption would not be high.[12] Some mercury vapour is absorbed dermally but uptake by this route is only approximately 1% of that by inhalation.[13]
In humans, approximately 80% of inhaled mercury vapour is absorbed via the respiratory tract where it enters the circulatory system and is distributed throughout the body.[14] Chronic exposure by inhalation, even at low concentrations in the range 0.742 μg/m3, has been shown in case control studies to cause effects such as tremors, impaired cognitive skills, and sleep disturbance in workers.[15][16]
I believe the mercury in lamps is simple elemental mercury. As such, the dangers of contact are minimal compared to other sources of mercury. I would suggest you have much more to worry about in what is in your food and what is in the atmosphere than what is in the lamps.

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