A plasma screen is a large widescreen monitor, from 32" to 84" in size, which has the advantage of being very thin so that it can be hung on walls. Plasma screens can be used with computers and video recorders/DVD players etc. A plasma screen overlay is a device that fits over a plasma screen. Plasma screens that have an interactive overlay on them work in exactly the same way as interactive whiteboards. The advantage of using a plasma screen is that a shadow is not cast by the presenter, unlike front projection interactive whiteboards. Plasma screens also have a lifespan of around 30,000 hours use. Projectors used with interactive whiteboards have an average of 2,000 hours lamp life and lamps for most projectors are costly to replace. The biggest disadvantage with the plasma screen is the screen size and the high price. However, Plasma screens give a far neater finish in a boardroom environment and far superior pictures when using video recorders, satellite systems or DVD players to show television or video.