Originally Posted by quantum
Nope, that seems like a ordinary light sensetive switches, you know... "when it gets this and this dark, then switch on whatever I have connected".
I just had a brief look at the specs for the VGA board and it looks like it's actually 0-12V, where 12V will provide 70% dimming. Personally I found the dimming not to be enough, even with 100% dimming it's too bright for night usage. That's one of the reasons I'll go with software instead.
Now, what you can do is to use something like this one: http://www.elfa.se/pdf/73/732/07322126.pdf
If you can find anything that you could feed with 12V and that outputs 0-5V then even better.
Hook it up to your gameport / or get a analog input board.
Now you can write you own software to read the sensor voltage and control the brightnedd/contrast instead _and_ you'll also get manual override.
If that doesn't suit you, use a regular photo diode to construct your own "light sensor" that outputs 0-12V to the VGA controller.