I have my rotational light dimmer and am wondering the logic behind it. If it is a potentiometer, when fully off, it should be wasting lets say 50V of power if not using a transistor. By logical design:
1) Should it have an extremely low voltage with a resistor and control a transistor to limit large power loss?
2) Is the dimmer a rheostat or a potentiometer?
If anybody has a answer, that would be great for my understanding. Thanks!
Dimmers traditionally involve a TRIAC that chops the ac waveform with a potentiometer controlling the duty cycle. These circuits cause highly distorted currents leading to a low power factor. Knowing this, you will easily find examples of such circuits online.
Varying current through an incandescent lamp with a series resistor (rheostat, potentiometer) wastes an unacceptable, even unmanageable, amount of power.
Note that this applies to incandescent lamps. There is no single standard solution to dimming LED lamps because of the varying drive methods used in the lamps.
MOST modern light dimmers are no longer a potentiometer or rheostat. The are a triac and the rotating dial you see is the "user interface", emulating the actions of the older rheostat technology. All the dial does now is advance or retard the firing angle of the triac done by the little firing board inside. That's why you see dimmers now with sliders or capacitive touch plates, they are just different versions of the user interface as a way of applying an analog value to the firing board.
There is some waste heat in the switching losses of the triac, about 1.5W of heat rejected per amp passed through.
Many LED light bulbs have triac dimming.