My VAIO advised me to switch to a White Background, to reduce power consumption.
But it seems contradictory to common logic. Its like saying a brighter Torch consuming less than a dimmer one.

Common Logic says that, Screen is BLACK when not using any POWER, so displaying black color should not consume any power (because without powering any pixel it gives black color)
Also a white screen gives me more light than a darker one, so it should use more Energy.

White Wallpaper => More Light Output => More Electrical Energy Consumed
Black Wallpaper => Less Light => Less Electricity Consumed

My question is - Is there anything wrong with the above argument ?

A Lighter Wallpaper consumes less power than a Darker one.

Is it true ?
If yes, Why ?