On Jan 27, 12:12 pm, CJT wrote:
wrote:

On Jan 27, 11:15 am, "Joseph Meehan"
wrote:

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

triacs.

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 ofRead my other post and think that through.




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
24.5watts

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.