I don't know if they have ambient light sensors to adjust the backlight (I don't think they do) but I don't see them as being particularly bright. I do tend to sit with my back to them.
They do show useful information relating to big engineering works, QR codes for various information, along with the animated 'filler' ads about groupsave or whatever. I've not seen any commercial advertising, but nor have I yet seen service information when approaching stations that would be useful (platforms, times, delays etc).