Even on a current new 2012 car, when the green LED clock inside the car is quite bright, but when the car's headlight is turned on, the clock dims down to only about 1/4 of its brightness, which makes the time hard to see.
I thought the clock requires merely a watt or even less for its brightness, and the car stereo which output at least 30 watt of music (if comparing a 30 watt speaker for the PC to the car stereo), won't be less loud when the headlight is turned on.
Why does the clock dim down so much? Is it explained by Ohm's law? Also, can't it be "parallel" instead of "in series" with the headlight, so that the brightness is not affected?