I installed sixteen dimmer switches around the house, for various purposes.
Don't have any problems at all, but am curious.
When a dimmer switch is turned down so the light is not as bright, does this
save electricity or does the dimmer switch disperse the voltage drop in
Thanks for the info. Bob
Modern home dimmer switch do save energy. Of course they do consume
some heat and most lamps when dimmed are somewhat less efficient. So if you
had 10 lamps in the room you could dim them all 50% or turn half of them off
and save a little more energy.
Wikipedia says the power used and light output of an incandescent bulb are
proportional to V^1.6 and V^3.4, so light is proportional to V^(3.4/1.6)
= P^2.125, no? Turning half off makes half the light with half the power,
but dimming all to 50% power only makes 0.5^2.1225, ie 23% of the light.
Making 50% of the light requires dimming them all to 0.5^(1/2.125), ie
72% of the original power. That's a lot vs a little more energy, IMO.
Then again, CFs are 4X more efficient, and some dimmable CFs have
a light output that's directly proportional to power :-)
You do save alot but im not sure about nicks numbers, To get an
incandesant to light when its output might be 1/ 100th or less I found
mine took 6-8v. I believe at 50% power you get less than 50% light
output. But incandesants can last 10 times more at 50% and nearly
indefinatly at 10% power, but this does not apply to halogens.
On Jan 27, 8:15 am, firstname.lastname@example.org wrote:
Another Nick classic. Quick with the numbers and clueless as
usual. The guy didn't ask if a bulb that is at half brightness uses
less energy. Any dummy knows that. What he asked was whether the
energy saved at the bulb just shows up as energy wasted at the
dimmer. Which of course it doesn;t because dimmers are Triacs.
I guess that could be called a trader4 classic since not all dimmers are
His numbers are correct and I believe he properly addressed the
question. Often a question calls for additional information.
Sorry, but I have to disagree. All Nick addressed was how much
energy is consumed in the light bulbs. That was not the question.
We all know a bulb that is burning at half brightness is going to use
less energy. The question was whether the energy saved in the light
bulb is just dissipated instead in the dimmer. And it would be if
the dimmer were a resistor.
But even if it were a resistor, the heat dissipated might not be much,
because the total resistance of the (presumably) series-connected
resistor and bulb would be greater than that of the bulb alone, so the
total system dissipation would drop.
The e-mail address in our reply-to line is reversed in an attempt to
minimize spam. Our true address is of the form email@example.com.
The OP says he installed 16 dimmer switches in his house. When is
the last time you saw a house dimmer switch that wasn't semiconductor/
Triac based? Every one you can buy down at the home center is.
And that was precisely the issue of the OP's question. Because these
type that use semiconducotrs and have been around for decades do not
just produce a voltage drop like a resistor would. If the dimmer was
resistor based, then it would just dissipate the energy instead of the
dimmed bulb and you would not save energy by dimming the bulb. That
was the question, which asked if the energy that doesn't go to the
bulb was not just dissipated as a voltage drop in the dimmer.
I see your point and you are correct. Inserting a resistor as a
dimmer doesn't mean that all of the power that would have been going
into the fully lit bulb now gets dissipated in the resistor dimmer.
But the amount the resistor has to dissipate as heat is still
substantial and why that method is not used for AC switch dimmers.
Here's a simple example. Let's take a 120W bulb connected to 120V,
which will draw 1 amp. So it uses 120Watts. To reduce the power at
the light to 50%, 60Watts, means the current would have to decrease
from 1 amp to .71amps. P=I**R That requires inserting a resistor of
49ohms in series. Inserting that, gives a total resistance of 169
amps, and a current of .71 amps through both the resistor and the
bulb. The bulb dissipates 60 watts, while the resistor dissipates
Which is a big waste of energy. Thirty percent of the power is going
to heat the resistor. Now consider that most of these switch dimmers
are rated at 600W. If you put a full load on it, it will require the
resistor dimmer to dissipate 122 Watts, which is a lot of heat for an
wall box, not to mention a lot of wasted energy. And of course, this
is to just dim the bulb from 120W to 60W. If you dim it more using a
resistor, it only gets worse.
That's why Triacs are used.
On Jan 27, 2:45 pm, firstname.lastname@example.org wrote:
You can go ahead and factor in the decrease in resistance of the bulb
at the lower light output if you want to. It doesn't change the
answer to the OP's question, which was whether typical light switch
dimmers disperse the power that would have gone to the bulb, which I
noticed you never addressed at all. And if you do factor in that the
resistance of the bulb decreases, it only makes the loss in a
resistive type dimmer, if one were to be used, worse.
Triacs are used in dimmers, because instead of acting like a resistor,
they act as an on/off switch on each current cycle, and hence waste
only a small fraction of the power that a resistor would. Instead of
harping on, for once just address the question that was asked and tell
us if you diagree with the simple statement in the previous sentence.
The type of dimmers under discussion are semiconductor based, using
Triacs. They are not variable resistor based, which would just
dissipate the energy that is not going to the lights, producing no
energy savings. The Triacs work instead by delaying turning on the
output voltage for part of the 60Hz sine wave, essentially chopping
off varying portions of the leading edge. That chopping action,
which turns a nice sine wave into something with a fast rising edge,
is also what produces RF intereference that is common with these.
There is of course some energy lost as heat in the dimmer, so they are
not 100% efficient, as you can tell by touching one. But a light
dimmed with one of these does save a substantial amount of energy.
I might add that while that is true for most all lamps, under some
conditions (generally when dimmed between about 40-60% halogen lamps will
actually have reduced life. Kind of knit picking. :-)
Also while and not sure exactly what trader4 was trying to say, but you
are correct about the savings not being directly proportional.
I put in newer electronic dimmers, and part of their advertisement,
was they reduce electricity, and extend bulb life. I don't
remembering it be 1 for 1 relationship. Example, 50% setting saved
40% and extended bulbs life like 25%.
Just what I remember...
tom @ www.FreeCreditCheckGuide.com
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