[LINUX] screen brightness is going crazy on revo with karmic

OK first thing, I am teaching myself the joys of Linux here

I have a revo 3610 which I have installed ubuntu karmic and XBMC 9.11. For some reason the brightness/contrast is dynamically changing on its own all the time and its very frustrating. Does anyone have any ideas as to places to start looking to figure out why it is doing this. It gradually gets darker and darker and then I have to do something with the mouse to get it back, almost like the XBMC dim screensaver but its very dynamic and affects the whole OS not just XBMC

Is anyone else with a revo and karmic having this issue. Its bloody frustrating that your trying to watch something and the screen is almost pulsating as the brightness is going up and down. Doesnt seem to matter if I use 185, 190 or 195 nvidia drivers. I do not have any screen saver or power management settings that should cause such an issue and it even happens on bootup at the splashscreen but not if Im in the bios.

I have tested other HDMI devices on the same TV and none cause similar issues so it must be either the revo hardware itself of karmic. I dont remember having this issue in jaunty but would like to avoid rebuilding back down to that

To me its sounds like your tv is doing dynamic back lighting

Thanks for the response. Could be but I have 4 other HDMI devices I have tried and it doesnt do it to the others on the same port with the same cable, will have a play but the light sensor option on the tv is turned off. Ive also found similar posts on some ubuntu forums which indicate similar issues with karmic so perhaps jaunty is the way to go, not sure. Being new to linux is can be a tad daunting, I found karmic is easier but need this fixed as it makes watching it annoying and Ive yet to retire my trusty old xbox/xbmc combo