Need to know if a rheostat cuts down the watts on the bulb. I don’t know anything about electricity- Example would be if I use a 60 watt bulb and turn it down low on the dimmer – does it still draw the same power? Last night we started an energy management course and I’m sure I’ll be back with some lame questions. Thanks, Rich
It’s not what you say or what you do- it’s how you make people feel
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My guess is you don't really mean a "rheostat", which is a variable resistor. Seldom seen for lighting control except in commercial settings.
Modern household dimmers are solid state switching devices that clip off part of the electrical sine wave feeding the light. So, yes, dimming lights with a dimmer control reduces the energy used by the lighting.
See: http://en.wikipedia.org/wiki/Dimmer
Mike Hennessy
Pittsburgh, PA
I wonder, though.....
They indeed do "clip" the sine wave, but IIRC they don't actually turn off, but rather dump the current to a heat sink.....but I could be RinCing......
"They indeed do "clip" the sine wave, but IIRC they don't actually turn off, but rather dump the current to a heat sink.....but I could be RinCing......"The common dimmer (vs some that are used for DC and maybe for LV switching power supplies (the non-magnetic "transformers")use a TRAC for the control switch.They turn off at the zero crossing. Then don't turn back on triggered some time later in the cycle. The more that trigger is delayed the smaller slice of voltage the lights gets and thus dimmer.When the TRAC is on there is a small voltage drop that is independent of current (I forgot if it is 0.7 volt or 1.4). The amount of current times that voltage is the power that is "lost" in the dimmer.It is very small amount. It will be less than 4 watts with a 300 watt lights.And the more that the switch is on (the brighter the light) the more time current is flowing through the TRAC and the more power that is lost.
Thanks for the education...
I find electricity both fascinating and mystifying. for example..."If you always need the light output of a 75 watt bulb, it is more efficient to use a 75 watt bulb than to use a 100 watt bulb and dim it down to the light output of a 75 watt bulb."Not sure how one would begin to think about verifying that claim......
Yes, best to "right size" the bulb.BTW, one of the dimmer brands (don't remember who, but it was a mainline company) got on the green wagon and can out with a "energy saving" dimmer.What it was was a standard dimmer with an internal control, so that as it was shipped, you could not get it to 80% (IIRC) of max brightness.
One way to think about it is that you can turn the dimmer down on a big bulb so far that NO light is emitted, since there's not enough power to make the filament glow, but current still flows. So you're getting zero bang for your buck. It takes more power to make a big filament produce as much light as, say, the small filament in a 3-volt flashlight. The bigger the filament, the less resistance, and therfor the more power it'll take to heat it up.
Mike HennessyPittsburgh, PA
Speaking as an Electrical Engineer, it's true. The reason has to do with temperature. The efficiency of incandescent lamps increases as the temperature of the filament increases, right up to the point where the filament burns out.When you dim a lamp you reduce the filament temperature, and that reduces lamp efficiency since proportionally more of the electricity is going into producing heat (or IR radiation) than light (visible radiation).
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce
Gee Joe, in an aggregate of your current 8 posts, you sure are sounding a lot more like an electrician, than a plumber...;o)
Incandescent light bulbs are most efficient when operated at their rated voltage. Reducing the voltage with a dimmer decreases the electrical consumption but decreases its light output more. I would not recommend a dimmer for energy conservation but to provide a variable light output were this is needed or desired for ambiance. If you always need the light output of a 75 watt bulb, it is more efficient to use a 75 watt bulb than to use a 100 watt bulb and dim it down to the light output of a 75 watt bulb.
Dimmers have an additional disadvantage when it comes to energy conservation that they are not compatible with most compact fluorescent bulbs which are much more efficient.
Thread hijack -
The dimmer switches in my house cause the AM radio to buzz.
I upgraded to a more expensive switch, the package sayid it won't interfere with AM radio. The buzz is significantly reduced, but it's still very noticeable. Any suggestions?
This doesn't need to be solved until next April, when baseball season restarts. That's my main reason to listen to AM radio.
Dimmers reduce the wattage consumed by the bulb, but proportionally much less than they reduce the light produced. Very roughly, if you reduce the wattage consumed by half you're reducing the light output by about a factor of four.
So it's much more economical to use the correct wattage bulb vs using a dimmer: incandescent lamps, when used without a dimmer (or a dimmer on "full"), produce light directly proportional to their wattage. (And it's more economical still to use a Compact Fluorescent Lamp -- CFL -- instead of a common incandescent lamp, though most CFLs are not dimmable.)
Thanks, now I'm not nearly confused as before!! No dimmer, no problem. On the down side of the new bulbs- cost a lot, costs to dispose of, don't work well in cold and can't dim. but still better. Rich
Note that HD (and probably Lowes) is now recycling used CFLs for free. No need to pay for disposal. (And, FWIW, it's less polluting, even in terms of mercury emissions, to just trash the bulb than to use incandescent, due to the difference in electrical usage. The amount of mercury in the extra coal burned to power an incandescent swamps the minuscule amount of mercury in the CFL lamp.)
Corporation: n. An ingenious device for obtaining individual profit without individual responsibility. --Ambrose Bierce