Many LCD monitors have a MTBF (mean time between failures) of like 50,000 to 100,000 hours. To be conservative let's say we took the 50,000 hour figure.
If you left your monitor on (I mean really on as if you were sitting in front of it) for 24 hours/day...it would take 5.7
years before you would reach 50,000 hours (11.4 years if we used the 100,000 hour figure).
Of course your not going to leave your monitor on 24 hours/day...in fact it may only be on a few hours/day. If you used your monitor 4 hours/day...you wouldn't reach the 50,000 hour figure for 34.2 years!!!
Of course there are other things that factor into the wear & tear on an LCD monitor...but believe me...unless you drop the monitor & break it. The monitor is going to last a long long time...and leaving that little white LED on when in standby mode will make very little difference.
Also, I'm willing to bet that you will probably upgrade to a larger monitor well before 34.2 years.
- Nick
p.s. Actually...if you pressed the power button on your monitor everytime you turned it off (so the little white LED would not be on)...you would probably wear out the power button much much faster than any additional wear & tear to the monitor by leaving the white LED on.