Many, many LCDs still use fluorescent backlights. Turning that backlight on and off prematurely ages the lamp. Just like a CRT, you want to turn it off (put it

Many, many LCDs still use fluorescent backlights. Turning that backlight on and off prematurely ages the lamp. Just like a CRT, you want to turn it off (put it into sleep) when the cost of the electricity outweighs the cost to lamp life -- e.g. overnight. You should always have a screensaver, even if it's just "blank screen," for when you lock your workstation for short periods.