Which uses more electricity, a 75 watt light bulb or a 150 with a dimmer so that it is as bright as the 75?

Which uses more electricity, a 75 watt light bulb, or a 150 with a dimmer so that it is only as bright as the 75?
If one uses more, does it use much more?
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Hi mm, me again...
Most dimmers (esp the reasonably priced ones) just stick a resistance in the line. So, they get hot (hence need a little ventilation, esp the high power ones). This consumes a fair bit of electricity. The smaller bulb w/ no dimmer is definitely more efficient. I think there are fancy dimmers that are electronic and chop the phases or something, but these still won't be 100% efficient.
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Well, every dimmer I've seen in the last 25 years is electronic. Resisntance dimmers are a thing of the past .... long, long past. Modern dimmers use a triac to "chop" the waveform and they do produce some heat. Also, when a higher wattage lamp is dimmed, the color changes and they become somewhat less efficient. I don't know exact numbers, but my guess is that it would probably cost more to run a dimmed 150 watt lamp to give the same light output of a 75 wat lamp
kevin wrote:

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This must mean you read my other post just now. I wanted them to appear together, but I wanted this one to be first. So I waited a full 45 seconds from posting this one until I posted the other one.
But still I think you got the other one first. I'm learning more and more about Usenet every month.

Still reading posts....
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The latter (phase choppers) as opposed to the former (resistors) are something like well over 99.9% of light dimmers in use, and 100% of light dimmers that you can buy at home centers and nearly all hardware stores and nearly all electrical/lighting supply shops.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Apparently I was misinformed about resistanced dimmers. I guess that also means that the dimmer isn't a huge loss, just the drop in lighting efficiency of the filament mostly.
The triacs still give off a fair bit of heat for high intensity lights, no? We have dimmers on some very bright lights at school (no idea how bright, but the administration complains if we turn them on saying they are expensive to run). Each dimmer has a separate 4"x4" wall plate with a 1/2" deep heat sink stuck on it.
Electronic dimmers it is then... -Kevin
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A common term of resistance dimmer now means that the load must be resistance and not inductive. That means in very simple terms the load must not contain a large coil of wire such as a motor,transformer, or flourescence tube ballast. They do make dimmers for the tubes.
The dimmer does generate some heat. Maybe as much as one or two watts of heat for each 100 watt bulb hooked to it.
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kevin wrote:

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The 150 on the dimmer. Light bulb efficiency drops off *a lot* the more you reduce the voltage. As the filament temperature drops, the bulb puts out a little less heat, but a lot less light.
For a 150W bulb to put out the same amount of light as a 75W bulb would require about 100W of electrical power.
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A 150 watter dimmed to the brightness of a 75-watter consumes about or maybe a bit under 100 watts. Given the dimmer likely to "lose" a watt or two in the process, I would say that a 150-watter dimmed to the brightness of a 75-watter ends up consuming close enough to 100 watts.
Assuming a 10 cent per KWH electricity cost, that extra 25 watts over the 750 hour rated average life expectancy of a "standard" 75W lightbulb costs $1.87. Even if the lightbulbs are at a "convenience store price" of $1.15 apiece and only average 500 hours actual life, you pay more if you even completely eliminate burnouts with 25 watts more power consumption per lightbulb.
- Don Klipstein ( snipped-for-privacy@misty.com)
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Don Klipstein wrote:

But at $3.19 per gallon of gas, that trip to the convenience store to buy a replacement light bulb (if not using a dimmer) will add another $1 to the cost. ;>)
Suppose you have a combo ceiling fan with four light bulbs in it. (The lights are wired separately through a switch.) You start out with four fresh bulbs. One eventually burns out. Do you replace the one, or all four? If you replace one, another will burn out in a few days. Replace that and another burns out. Drives you nuts. Replace all four when the first burns out and you could be wasting good bulbs because of one bad bulb. What do you do?
That's why I prefer a dimmer with higher wattage bulbs. It greatly extends the bulb's life, and then I'm willing to replace all four at once. Not the most frugal, but lessens the frequency of my chances of falling off the ladder.
Lena
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If I were worried about the ladder, I might do that, but I wouldn't throw away the good bulbs. I'd put them in a used bulb box and use them in lamps and anything more accessible than a ceiling fixture.
Me, I change the bulbs in one bedroom while standing on the mattress, which can be very challenging. In the other, I stand on a rolling, reclining, swivel desk chair. Well I used to, but the very heavy one broke and the newer lighter one might not work.

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Lena wrote:

I agree.
I installed "hidden" dimmers for the "vanity lights" in our bathrooms and set them just a little down from full brightness. It seems like I've hardly ever had one of those bulbs burn out in the twenty years since I did that.
Jeff
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This is even more true if you live in Kansas, where the new "light bulb convenience" law states that you MUST go out to buy a new bulb IMMEDIATELY on discovering the old one burnt out and you MUST NOT use that trip for anything other than to buy ONE light bulb. It is a class one felony for a consumer to get 2 bulbs at once.

Don't forget, it's a separate trip to the store for each bulb.

BTW, in case you forgot this is not a serious message.
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mm wrote:

As bright means almost same not equal. So the question is moot. For same kind bulbs takes same amount of energy to produce same Lumen(brightness)
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Tony Hwang wrote:

No, the balance between heat and light changes.
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CJT wrote:

I'd also say that the meaning of "as bright" is that the two would be equal brightness, not "almost same." Particularly in context, the question was clear.
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mm wrote:

No matter how you dim it, the 75 will be more efficient or brighter if you like. However the 150 watt will last a lot longer.
The hotter the lamp burns the more efficient it will be and the shorter its life will be.
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a lamp dimmed to half its wattage will last so long its filament wouldnt burn out but outgass or redeposit on the inside of the glass bulb making the bulb very dim even if run at full voltage undimmed.
much of this can be elminated by using compact fluroscents, much more feeicent with less heat and long life.
most shouldnt be used on dimmers
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Thanks to everyone who answered. I'll use all this info when deciding what to put in my three locations with dimmers. The 150's really are expensive, too, like that guy brought up a few weeks ago. Very annoying when I knocked the lamp off the kitchen table.
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