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Does a dimmer switch rheostat consume the electricity that the light fixture is not receiving?

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2015-07-15 21:41:03
2015-07-15 21:41:03

A little.

First off, most modern dimmer switches aren't rheostats. Those have been supplanted by TRIACs (triode for AC), and later, IGBTs (insulated gate bipolar transistors). For both of these, their mode of action is to change the duty cycle of the AC wave (duty cycle is time on versus cycle time) such that less power per cycle is put through the bulb. This is more efficient than a rheostat, in that, there isnt as much resistive loss across the dimmer.

The resistive loss is where the "a little" comes in. For all three types, a small amount of the power put through the dimmer is dissipated as heat - however, this is significantly less than the reduction in output power to the bulb, whatever the type.

An ideal dimmer would have 100% efficiency - that is, for a given setting, it would dissipate no heat, and the bulb would be the only thing on the circuit consuming power. However, no component is ideal, and modern dimmers typically consume under 1% of their power throughput (so if it's passing a total of 1W, it'll consume less than 10 milliWatts).

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