Issue: When connecting your android device to TV or projector using HDMI out, you can’t turn the Android device display off.
Finally, I found the best solution to turn my android tablet screen off when using HDMI out. (tested on Acer Iconia A500 tablet)
Solution: The solution is to use RootDim, you can download it for free from Google Play Store.
Requirement: need to root your Android device.
How to do it?
1./ Download RootDim from Google Play Store
Download from your Android device click here
2./ When connecting to HDMI out port, run the Root Dim, then click “min” from “min, 25%, 50%, 75%, 100% ” options
Warning: Do it at your own risk. To turn the tablet screen on again, just press power button.