By default Windows 7 turns of (stand by) monitor every 20 minutes. So I guess, it should be OK to turn off LCD (manually push the power button) when I need to leave for over 20 minutes.
In this thread: Should I use a screensaver or just turn the monitor off when I am done?, snicker said:
Powering off modern monitors will not cause any detrimental harm to them.
If you want to save power, it is best to turn them off completely when you are not using them.
But TandemAdam said:
if you are going to be going on and off your computer constantly, then I would just let the screensaver run, as turning you monitor on/off all day could eventually cause more damage.
and torbengb said:
turning a device on and off causes wear because the electronics expand and contract a little when they heat up and cool off. That can eventually lead to a failure.
In summer, my room temperature is 28~31 Celsius degrees. But In winter, it could drop to 3~8 Celsius degrees. Turning on/off LCD in winter seems to cause quite big temperature change to the LCD.
My question is: Does "frequently" (10 times a day) turning on/off LCD shortens its lifespan, especially in my winter? (I plan to use my monitors for over 5 years)