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Light Dimmer Switch

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RTFishall | 18:46 Mon 10th Nov 2008 | Science
12 Answers
When I turn the dimmer down on my light switch, am I saving electricity or is it just being wasted in a resistor?


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You are wasting it. It will be turned to heat and sound (the buzzing you hear).
Yes you will be saving energy its controlled a triac or it was 20 yrs ago
In actuality, both previous answers are correct. If the dimmer is an older rheostat type that simply controls the voltage going to the bulb, no savings will be realized since the electricity is converted to heat. However, as the second anzwer implies, newer, electronic dimmers control the amount of time the electricity is on... i.e. reaching the light bulb. It happens so quickly the cycle of off-on cannot be perceived by eyesight. The more the bulb is dimmed, the more one saves. Additionally, the dimmed bulb last a lot longer... Unfortunately, you can't dim most fluorescent bulbs...
Well Clanad ive seen domestic light controllers clip or chop the power never seen a rheostat one it would need some sort of back box for that type ,when you say old how old (ime nearer 80 than 70)
all the best lol
Hi ya, bentaxle. (great name!)... here in the U.S., most of the rheostat type dimmer switches disappeared about 10, maybe 20 years ago. I've a neighbor that still has one and it's self-contained within the switch box itself... Hums a nice tune, which I can decipher...
Question Author
Thanks for all your answers (to date). But I'm still not sure, is the �5 dimmer I can buy at B&Q saving my electric bill? I've asked Customer Services at B&Q but all they say is "Would you like our new energy saving light bulbs" lol

PS. And that's another question!
Gosh, I'm glad that we didn't have dimmers when I was a lad and young man because they would certainly have been rheostats, wasting as heat the energy that would otherwise have gone into the lamps.

Modern dimmers work by progressively clipping the sinusoidal waveform of the a.c. voltage, thus reducing the RMS value of it. That's why they remain cool.
Well Rtfishall I can only say I got rid of my dimmers when the low energy lamps came out as they dont work with them ,so if its to save money go for the low energy lamps also
you wont be able to buy tungsten lamps in a few years
Like I said clip ,chop ,or burst fire its just another way of controlling the RMS, we also had a dimmer 60 yrs ago we called it a gas valve and mantle you see theres nothing new in this world
all the best Chakka
Hello Clanad I still marvel at this www keep thinking its a chap down the road ime talking to ,any way the name was an old fishermans nick name it was that or brokendish his brother
all the best
Question Author
bentaxle, The only trouble with low energy bulbs is the terrible colour temperature of the light. I've even tried the more expensive "Daylight" type and there even worse. Still I've got about 100 years supply of incandescent bulbs stored in the shed, so I guess I'll stick with my more welcoming (and smaller) bulbs and dimmers for some time yet. ;)

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