HUD subtle flicker?

I've noticed that the HUD brightness flickers subtly. Hard to see when the car's moving, but sitting still I see it. I can't find any threads on this, so wondering if it's just me.

(Thanks for your feedback! This is a 2018 Prius Four. And it's a small dimming where it stays at full brightness for 4-10 seconds, then dims subtly for 2-4 seconds. Not any kind of flashing. I first saw it in the evening, not yet dark but not full daylight, and assumed it might be something like shadows and light falling on a sensor that adjusts its brightness. I haven't noticed it in bright light, and can't remember if I've seen it at night. I have seen it in our underground garage. When the car's moving, there's enough motion of things that I would hardly notice it if I hadn't been sensitized in a stopped car.)

 

I noticed it very strongly yesterday in our complex's garage. For some reason, the car was slow to switch from day to night mode (navigation flipping from white to black, etc) and as the car went under overhead flourescent lights, the HUD dimmed very noticeably in response.

So I think what I've seen is a combination of two things: a) the HUD does not have as strong a hysteresis-prevention as the rest of the display, and b) the HUD adjusts more strongly in daylight conditions. This may be due to the HUD actually having to adjust more rapidly since it's in your line-of-sight, or it may be that they didn't figure it's worth the extra time and effort to make it work differently.

So I'm very sure now it's a real effect and it could be quite normal, but require just the right conditions to see. It's possible that our Prius' environmental light level sensor system is defective, I guess, and I'll report here if that happens. Thanks all!