Does a dimmer switch use electricity?

[Pebbilita]

Hello,
How does a variable resistor change the flow of electricity? For example, on a dimmer light switch does it use any of the electricity that flowing through it in order to dim the light? Thank you

[Loosehead]

The light is dimmed by the variable resistor reducing the amount of energy available to power the light. It does not "use any of the electricity" to actally dim the light, the electricity is evvectively strangled in it's progress toward powering the light. Hope that makes sense.

[Pebbilita]

Thank you! but what gives the resistor the power to ...Strangle?

[Loosehead]

The resistor is made of special "resistance" wire, that is wire that is a very poor conductor. The length of that wire that is in the circuit is variable depending on the position of the dimmer switch so for max brightness no resistance wire will be in the circuit for min brightness then the resistance wire will be fully in the circuit. The resistor is not "powered" as such.

[Pebbilita]

Excellent!! Thank you!

[TeeGee]

You'll probably find that a resistor-type dimmer switch gets warm in use, so that a small amount is being translated to heat energy within the switch. So Yes, a dimmer switch does use energy but a very, very small amount.

[Tim123]

Modern dimmer switches are far more complicated than a simple rheostat.

http://home.howstuffworks.com/dimmer-switch2.h tm

[TeeGee]

Indeed so, Tim123 but they still get a little warm, you don't get owt for nowt. So my above observation stands.

[buildersmate]

Your observation does stand, but its simply not true that a rheostat type dimmer uses little power. To knock a mains 60W bulb down to one quarter of its rated power (15W) requires a 1k ohm resistor of 15W rating. Such beasts are large wirewind affairs that get very hot. As much power would then be lost in the resistor as is consumed by the bulb. Tim's right.

[Pebbilita]

Sorry for sounding slow.... so does that mean then that the resistor IS consuming some form of energy? Which contributes to an electricity bill? ( even if very small?)

[TeeGee]

Any, or all, electrical or electronic circuit(s) consume some power when in use. Albeit sometimes very small. Afterall they rely on there being a potential ( voltage ) difference and depending on the resistance ( or impedance ) some power is inevitably consumed.

[Loosehead]

the point is, as explained in varying ways above, the energy that is being prevented from getting to the bulb is being dissipated in the form of heat. Essentially the circuit uses the same power regardless of the dimness of the bulb so it is not taking power to run the function of dimming it is taking power and turning it to heat as a means of stopping the full power getting to the bulb.

[TeeGee]

Looseheads answer is only correct in the case of a direct rheostat, but even the modern type of dimmer uses a variable resistor of some form to control the device, so Pebbilitas question can be answered in a quite straighforward manner and is, as I said earlier -

Any, or all, electrical or electronic circuit(s) consume some power when in use. Albeit sometimes very small. Afterall they rely on there being a potential ( voltage ) difference and depending on the resistance ( or impedance ) some power is inevitably consumed.

[mjd]

what has been said to date is true as far as it goes but only relates to resisitve dimmers. Almost all modern dimmers utilise semiconductors called thysistors. The brightness of the light is controlled by turning the thyristor on (and allowing current to floe through the light) at different points in the mains cycle. Turn it on at the beginning and current flows all the time, max.brightness. turn on very late & current only flows for a short time, very dim light.. The angle at which the turn on occurs is controlled by a variable resistor which dissipates v. little energy. When off the dimmer consumes hardly any energy.

[TeeGee]

Surley mjd, when the switch is off, it's off, isolated, dead.

[buildersmate]

Yes, exactly the point! When its off, dead, not working, not conducting it uses no power. When its on, working, conducting, a thyristor has very little resistance so uses very little power also!!
Result - the thyristor switches fast between these 2 states in a wave chopping action, but uses a tiny amount of power itself. The proportion of the ON to OFF time determines the brightness of the lamp.