In my app I have to turn off the screen but keeping active the touch screen.
I use this code:
Dim Phone_Brightness as Phone
Phone_Brightness.SetScreenBrightness (1/255)
I tried it on an X8(OS 2.3.3) and an LG P500(OS 2.3.3) and it works perfectly (all black screen), but on Galaxy S2 (OS 4.0.3) the screen doesn't become completely black.