# Dimmer/Toggle Switch

Discussion in 'Electrical Engineering' started by Kissi Asiedu, Dec 31, 2005.

1. ### Kissi AsieduGuest

Would the replacement of regular toggle switch with a dimmer have any effect
on energy savings? What I want to know is that, if I dimmed a 40W light bulb
for about 3hrs compared to a switch that stays on for the same period of
time, would the electric bill be the same?
Thanks.

2. ### Rich256Guest

Depending on your rates, it might cost you a penny to run the 40W bulb for
three hours. Put in a dimmer and you might save 1/4 of that. You might
save 10 cents a month.

3. ### EpsilonRhoGuest

A common question is whether dimmers actually cut electrical use.
Modern ones do! Very old resistance dimmers didn't (some folks still
call dimmers "reostats".)

Sorry, but this is not true. Reostats do reduce total power consumption,
although not efficiently.
Example: Bulb = 120 W @ 120V; I=1A: R=120Ohm
Add 120 ohm resistor in series (set with the reostat):
Total power: V^2/Rtot = 120x120/240= 60W! The bulb uses 30W and the reostat
30W,
but the total power is half of the lamp used without reostat.
You could do the generic algebric calculation and find a hyperbolic relation
between total power
(y-axis) and total resistance (x-axis).

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