Darken Viking Pro tablet screen when using hdmi to t.v.

[zhong]

I have a Viking Pro 10.1 inches model- RCT6303W87 DK

I wish to automatically darken the screen when I use hdmi cable plugged from tablet to t.v. video play.

I try to adjust time out in settings of hdmi but it doesn't work.

Is there a way to darken the tablet screen so it won't burn the screen ? Cause I don't need to have the tablet screen on when playing on lcd t.v.
If there is a way to darken the screen when in hdmi mode. If so, where in settings and how to do it ?



Thanks