Does a dimmer switch (aka: rheostat) on a light reduce power consumption?

Question

Will installing a dimmer switch reduce my electric bill?

Answer 1

The correct answer is yes, provided you are comparing it to operating the light at full intensity. A dimmer reduces the power output of the light, and therefore allows you to use less power when you don't want as much light.

Many ill-informed people will claim that dimmers don't actually save power consumption because it converts it all to heat in its resistive windings. This is a myth, and they are not engineers. At least...they shouldn't be. The truth is that the heat generated by a rheostat is a fraction of the amount of energy actually attenuated. The heat is generated simply due to the fact that real rheostats are imperfect devices, and suffer some real-world energy loss. Think about it. You have a light bulb that's burning well over 200 Degrees Farenheit. If you were to really put a "dimmer" device on that that changes all of its power to heat...your "dimmer" would get blazing hot wouldn't it? Does a Rheostat get that hot? Nope. Not even old-style dimmers. New solid state dimmers are even more efficient, and incur even less power loss. A Rheostat reduces the current flow across the appliance, reducing the power consumed by the system, period.

Other folks will point out that if you run the light with the dimmer but at full blast, that it will use *more* power, bcs of the addional loss in the system. They have a point, but fail to see the larger picture. The energy loss of incorporating a dimmer device will indeed consume more power at full blast than one without a dimmer device, but will give you the ability to save significantly more power in allowing easy dimming. The alternative is moronically having to replace the high-wattage bulb with a lower wattage bulb every time you want to save power, to save the milliwatts of power loss you'd have incurred by incorporating a dimmer.

And of course, I woud add that it would be vastly more effective to use a more efficient light source to begin with as a power-saving measure. Incandescent lights produce more than 90% heat, and only about 10% light. Flourescent lights, on the other hand produce much less wasted energy in the production of its light.

Answer 2

You are asking two different questions here - which may well have two different answers.

The two questions are - will it reduce power consumption? And will it reduce energy cost? These are not necessarily linked, as you can see below.

An older dimmer (the carbon plate resistance variety) will somewhat reduce power consumption by making a parallel current path. Depending on the dimmer rating, it may or may not actually reduce power consumption (as an approximation, going from 100 percent to 75 percent will save you something, but going all the way down to 50 percent will simply dump the energy into the device instead of the lamp).

In comparison, using a rectifier type dimmer (the modern kind) will NOT lower your power consumption because it introduces harmonics into the system - both to your light and back to the utility. These have to be accounted for, so the 'apparent' power usage will be higher, even if the 'real' power usage remains the same. Depending on how your utility prices your power, this may mean you actually pay somewhat MORE for power.

Of course, the major "loads" in a house are (in order of magnitude): electric baseboard heating, electric water heater, electric dryer, refrigerator, freezer, .... and way down at the bottom, lighting and electronics.

Answer 3

This Site Might Help You.

RE:
Does a dimmer switch (aka: rheostat) on a light reduce power consumption?
Will installing a dimmer switch reduce my electric bill?

Answer 4

Dimmer switches used in walls are not rheostats in the power sense.
A true rheostat dimmer uses a large carbon plate to increase the total resistance in the line so the current flowing to the bulb is less. It does reduce power usage because the total current times total voltage (watts) is less, although it gives off power as heat in the carbon disk.. Used to be used to dim stage lighting.
Modern dimmers use triacs and SCR (silcon controlled rectifiers) to dim lights. They do this by waiting during each cycle to turn on the voltage more or less later in the cycle. When the power is a narrow little spike, the bulb is dim, when it is almost the full half cycle, it is bright. The circuit uses some power (gets warm) but nothing like full resistance devices.

Answer 5

A dimmer switch does reduce the power consumed. Installing one will only reduce the power if you turn it down. You can get the same or better result by installing florescent bulbs in place of your incandescent bulbs - and not have to stumble around in the dark to save energy.

For example there are florescent bulbs with an equivalent 100 watt light output that use only 23 watts. If you were to replace your 100 watt incandescent bulb with a 23 watt incandescent bulb or use a dimmer to turn down the power to that level. You would find it darker than you would like.

Answer 6

Does Dimming Lights Save Energy

Answer 7

I have heard both answers to this, even by people who should know. I do believe the dimmer switch absorbs some of the power use, but it also reduces consumption some.

Answer 8

it might, but then...in using a rheostat to dim stuff, that means that there will be higher resistance in the circuit (in the rheostat) to give a dimmer light, hence some energy may be lost to that higher resistance too! so its not a total energy saver!

Answer 9

Yes, when your light is dimmed, it is using less power.
Try using flourescent bulbs, too.

Answer 10

A rheostat will not save you a lot. It will dissipate power across the resistor instead of the light bulb.