Please check your Instrument Panel Dimmer control

This is a feature isn't it? It gives you the option to use it this way.

 

I believe Phil is trying to say that instead of dimming it is either at full intensity or off.

 

My dimmer works as it should, a gradual progression either way.

 

i will check mine. from memory, it works, but i keep it at full bright. it is a rheostat, isn't it? or have they developed an electronic control with old fashioned wheel?

 

Ours works as a dimmer, with full bright after turning past the click at the top.

 

IIRC, daytime and nighttime functions are different. Nighttime varies, but daytime is light or dark.

 

No need to wait for nightfall. You can cover the ambient light sensor on the dashboard with a dark towel.

 

I don't use the auto light option. I use the day lights, and then on. The dimmer works the way you say, either full or light, this way. I have to manually switch it. If you have your lights on the auto setting, I believe it does the auto dimming as well.

 

I like my backlighting as dim as is readable so that I can preserve my night vision. Several times I have dimmed them to the point that the HSI screen isn't showing anything, and the first time I thought something had fried.

 

I would guess a potentiometer versus a rheostat. Much less electrically noisy, and brightness is probably a function of an ECU somewhere using the reference resistance provided by that thumbwheel.

 

Okay, to satisfy my own curiosity, I conducted a test last night and this morning. I left the light stalk in "auto" position in both cases. At night, the thumbwheel acts as a variable dimmer. During the day, the thumbwheel is either fully dimmed or fully bright, no variable dimmer. That's the way it works on my Prius.