Can cause problems apparently. This is more of a bug report than a question... but maybe I am doing something wrong.
I wanted to shutoff the monitor, so I saw a Perl script that did that, and thought I can do that in TCL real quick. So I did, but it doesn't work.
I broke down the steps here that cause the screen to stay black, I can restart lxdm and get it back.
xset dpms force off
tvservice -o
xset dpms force on
tvservice -p
apparently, thru my testing, you must have the hdmi powered on before dpms turns the monitor on or you end up at a black screen that I could only get around by restarting lxdm or rebooting.