When you press MENU, you should see an option for SETUP. Scroll down to that and click the arrow on the remote to the right. Scroll all the way down, and one of the last options is LIGHT EFFECT. Click to the right again, and you'll have the option of Off, Standby, Watching and Always on. That will allow you to power down the light.

From page 28 in the manual:

Does that help?