medical question

I don't know what search term to use to look this up for myself. It's for a fic. You know how when doctors need to look at X-rays and suchlike, they stick them up on a sort of white wall that's really one big light, to see the scan properly? What on earth is that called? A light wall? They do this in House all the time, I've seen it on the X-Files before, I'm sure every medical drama known to man has featured it. It must have a real name.