A flat panel display technology which consists of three tiny cells for each pixel. Each cell contains a gas which, when electrically stimulated, emits ultraviolet light which, in turn, activates a phosphor coating on the edge of the cell facing the viewers. The phosphors for the three cells are selected for red, green and blue light. Plasma displays have the advantage of being relatively modest in thickness (typically around 75 to 100mm including casing). Some models require internal fans for cooling, but for home theater use those without are preferable to eliminate this source of noise. Older panels may suffer 'burn-in' in which a ghost of the image is retained if left displayed for too long. But this can be easily avoided simply by not leaving menus and the like displayed too long. Some models also incorporate TV tuners and speakers and are thus called plasma TVs.