There is a traffic light near me that has three lights on it, and there is a noticeable difference between when the first light goes from green to orange to red and when the second goes through the same progression. My friends thought I was insane until I took high speed photography of the same traffic lights and proved them that it was off by the tiniest amount (don't remember exact figures). The same thing can be said for PWM'ed LED's, such as the ones in certain cars...