It takes lots of light to deliver bright, crisp images on your rear-projection TV, but that same light leaks through to the screen during dark, Perfect Storm--style gloomy scenes, hindering detail. To darken the blacks, a growing number of LCD and DLP rear-projection-TV manufacturers are turning to mechanical apertures that can limit the amount of light that reaches the screen. HP, Toshiba and Sony, among others, are using a dynamic iris, which automatically narrows like a camera's aperture to reduce the amount of stray light. Mitsubishi´s approach, on the other hand, works like a shutter, quickly opening and closing after light leaves the DLP chip. The controls continuously monitor video, limiting the light output by as much as 75 percent during dark scenes. The resulting contrast ratios--the difference between the blackest blacks and the whitest whites--can be increased fourfold to about 5,000:1, or slightly better than plasma and direct-view LCD TVs.