Display technologies (such as CRT, Plasma and others) when left with a static image for prolonged periods, end up with the static image burned into the screen. This is especially visible when viewing darkly lit content.
The burn in effect isn't limited to static images. A TV station's logo can burn into the screen as its position is fixed and visible for long periods or when viewing a lot of 4:3 content on a 16:9 Widescreen TV (at the original aspect ratio), the black bars on the sides of the screen can lose contrast with the rest of the display area.
WhiteWash Wizard can reduce and eliminate the burn in effect by slowly forcing pixels through a bright and dark cycle which can help restore their contrast range.