Comment Re:Not just cost, but optics (Score 2, Informative) 685
Diodes have a very sharp turn on, so from off to full on is a very small voltage change. To alter the brightness of an LED you pulse them at some cycle rate. For dim you turn them on for a little bit every cycle and for bright you turn the on for most of the cycle. That's pulse width modulation. If you don't use a high enough frequency then you can see the flicker especially when your eyes scan across them.
