Is that my rear screen heater button?

[cheapo]

LoL! A bit late, but I just tried it in the dark. (ooer missus!) It does get brighter as I push it in. (facepalm)(ooer missus!)(facepalm) ROFL! But the brightness goes back to nothing when it's released. On the few cold mornings when I could have done with it, it had no effect, so I stopped using it and decided to ask.
Dammit, I'll have to get on me hands and knees and look at the blimmin fuses. I need to check them as the stereo doesen't work either.