Thank-you for your question.
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
"Some lower-end front-projection models don't produce a bright enough
picture to view it in a fully lit room, and you'll have to dim the
lights to get a good view. The lumens value indicates the brightness
of the projected picture; the higher the lumens number, the better."
If you require any further assistance on this subject please ask for
clarification before rating my answer and I will get back to you as
soon as possible.