I saw a strange effect with the rearview mirror in my (2 months new to me) LR3 yesterday. A car was behind me who’s headlight bulbs seemed to be jittering horizontally. It was a newish Toyota Venza with LED bulbs. It was so striking, my first reaction was that it was a custom aftermarket thing, like pulsing lights on a motorcycle. Looking at the same car in my side mirror showed no vibration.

At one point, there was also a car with halogen bulbs visible in the mirror at the same time. The halogen bulbs appeared steady while the LEDs were jittering (again, only horizontal, no vertical component to the motion). I even turned around briefly to look with my naked eyes, and there was no jittering.

Is this related to the auto-dimming function of the LR3 rearview mirror? Some kind of frequency-based pattern between the LEDs and the mirror electronics? I’ve never seen this before.

 

LEDs are usually PWM (pulse-width-modulation) controlled. So if there was just the correct road vibration or music playing, the mirror was vibrating just right to cause that. Sorta like when shooting a video of a helicopter and the blades appear to not be moving or moving slowly. Frame-rate sorta stuff. The dimming in the mirrors we have are electrochromic and is based on variable voltage and is more similar to an old calculator display, except a little more sluggish by design to not result in super fast adjustments.