XNA game on Xbox screen dimming

Question

I have a made a game for the Xbox 360 using XNA and whilst testing the game the screen seems to dim every 30 seconds. The way it dims is as if I have been away from the Xbox for a while. If I press the Xbox guide it goes back to normal. I've tried googling this issue and i've found a few people who have had the same problem but I couldn't seem to find any replies on those posts. If anyone knows what the issue is and how I could fix it it would be of great help as this is the last kink i'm trying to resolve with my game.

Answer 1

Just to convert my comment into an answer:

Many modern TVs and some monitors have a "dynamic contrast" feature where, if the displayed image is predominantly black, the intensity of the backlight will be reduced.

(Often it's really annoying, just making high-contrast black-background scenes go dark for no reason.)

The backlight can also be turned down as a power-saving feature, kind of like a screen-saver.

You could test on a monitor without this feature, disable this feature in your TV settings, or use a scene that isn't so dark.