Originally Posted by BarryD0706
You can't use a pot to dim LEDs. You have to use a pulse width modulator to dim them (and those can make RF noise which interferes with things like TVs).
Not entirely true. Depends on the LEDs. LEDs used for white light are about 3.3 volt devices. To drive them off 12 volts, various techniques are used. Simplist (cheapest) method is to connect some (say, three) LEDs in series - getting the total LED drop (in this example) up to about ten volts (3 time 3.3 volts), then add a resistor to drop the remaining voltage (to the 12 volt supply). Simple and cheap, but the light output varies noticeably with supply voltage (e.g., on battery alone vs shore power - converter "on"). This type of LED will dim with a simple series resistor (a potentiometer or "pot") and will not cause any RF noise - will not interfere with TV or radio reception. I have this type of LED in my RV and use a simple series resistor to dim them - the light variance with supply voltage I find acceptable, and I have no interference problems.
Alternate LED drive circuits typically include an IC in the LED to "adjust" the incoming 12 volts to the LED's required ~3.3 volts. This type of LED driver will have less brightness variation with incoming supply voltage (battery vs shore power). Putting a resistor (e.g., a "pot") ahead of these ICs can have varying effects - depending on the specific IC. Pulse width modulating the incoming power to the LED rapidly turns the LED on and off, varying the "on" time to vary the effective (time averaged) light output. The LED is always "on" at ~the same brightness, but for more or less time - resulting in perceived brighter or dimmer light. Because this pulsing must occur rapidly to avoid seeing "flicker", the circuits are switching the drive current very fast - potentially causing RF noise - and TV or radio reception interference.