2006 Prius speedometer automatically dims with bright sun.

So have you used the switch to turn it to full brightness and you still can't see the display in the sun? Are you using polarized sunglasses. removing them helps. I think you can adjust the day, night setting on the display by going through the menu's.

Normal the little bubble on the dash close to front edge of windshield is a load sensor when dark lights stay on bright when sun is out dims the lighting cover sensor problem solved