Why do LED lights look like they are flashing quickly???

I have this ongoing discussion with my spouse about LED lights. Each time we see a new Cadillac with those fancy LED tail lights she seems to think they are flashing so fast they appear to be on steadily. She says it seems like they are "vibrating" is the only way she can describe it. Anyone else think so? Anyone know anything about LED lights or how they work? Or is sleep-deprevation taking her over????

Public Comments

1. led lights can "vibrate" or go on steady. I don't know why or how they can do this. I have astro jax. which are basically led lights on the ends of strings. when you spin them they make cool designs. you can set them to be on steady or vibrate. when you set them to be on vibrate they look steady untill you spinn them, then you can see that they are not steady.....so i think cadillac uses leds that vibrate because they look cooler when the car is moving..... does this answer your question?
2. It is common for LED alpha-numeric displays to flash rapidly. I think I saw the same thing with a new car tail light. Why would the manufacturer do this? Good question. My guess is that it is a simple way to change the brightness. Step on the brake pedal and the ON time gets longer and the OFF time gets shorter. Then the light looks brighter.