How much electricity goes a 50 inch plasma screen tv use?

Plasma screens are becoming more efficient as their designs are improved. Typically, a modern plasma screen will use in the region of 300W although the power drawn is dependent on the image up to a point. A bright image will draw a little more power than a black screen.

Every model is different so it's worth taking a look in the manual for each model. If the question is asked for energy conservation reasons, be aware that turning the television off whenever it is not being watched and turning the power off completely can often save more energy that choosing a marginally more efficient model.