I got the following info off the net: Brightness on HDTV sets is often measured in cd/m2 or candela per square meter. This indicates how well you can view the TV in brighter lighting conditions. The higher the value the brighter the screen will be and the easier it will be to see in bright light conditions. For examples, you are probably aware how difficult it can be to watch a TV set in a bright room or even use a laptop outside, this is because of the brightness of the unit. A typical TV set has a brightness of 350 cd/m2, an older laptop screen of 400 cd/m2 and a new HDTV can be upwards of 1000 cd/m2. Therefore if the room you will be watching your HDTV in is often bright you will benefit greatly from a higher cd/m2 TV set as it will help deliver a higher quality picture. "Brightness deals with the intensity of the light that one can see and is measured by candelas, as in candelas per meter squared or cd/m2, also referred as nits. It can make a significant difference in a user's visual experience depending upon the environment and the content being viewed. If you watch TV in a sunlit room, you want a brighter screen than when you watch TV in a dark room. A typical CRT picture tube has an average rating of 350 cd/m2. A key issue about screen brightness is uniformity or is the screen's brightness the same throughout all the areas of the screen? When a CRT was curved, there were differences. Flat screen CRT's display more uniform brightness levels so, overall, the image appears brighter to your eye. Flat panel screens, LCD and Plasma, generally have uniform brightness levels and, for now, that is one of the variables that limits screen sizes. That's why LCD screens are typically up to 36 inches (diagonal) and Plasma screens run to about 60 inches. An older LCD screen might have had 250 cd/m2, when used as a computer monitor, but can now achieve well over 400 cd/m2 but there is a cofactor that needs to be considered. LCD panel screens are lit with built-in fluorescent tubes above, beside and sometimes behind the LCD. This lamp, usually a Cold Cathode Fluorescent Lamp (CCFL), produces little heat, is highly efficient, and has a long life span. A white diffusion panel behind the LCD redirects and scatters the light evenly to ensure a uniform display. This is known as a backlight. When that light goes out, you can barely see the image on the screen. This principle also applies to LCD and DLP projector and rear projector TV models." Read the whole thing here: http://answers.google.com/answers/threadview?id=566806
