Re: [Phys-l] About black zones in screens

[Scott Orshan <sdorshan@aol.com>]

The TVs advertised as "LED" TVs are LCD TVs with white LED light sources 
instead of fluorescent light sources. LCDs only pass light, they don't 
generate it, so they need a light source. Some of the higher end LED TVs 
use zones of LEDs to allow segments of the screen to be dimmed to 
produce better blacks.

There are high end projectors that use colored LED light sources with a 
DLP imager, but you don't have that in your classroom.

http://hometheater.about.com/od/televisions/qt/ledlcdtvfacts.htm

To address another comment about color mixing, I've written about this 
before on the NSTA list, so I won't go into any detail here, but as far 
as physics is concerned, there is no such thing as color mixing the way 
it is described in textbooks. It's all an illusion caused by the way the 
human visual system works.

Red plus Green does not make a new wavelength of light - it only *looks* 
yellow.

     Scott

On 11/18/2010 12:00 PM, phys-l-request@carnot.physics.buffalo.edu wrote:
> Date: Thu, 18 Nov 2010 14:15:49 -0300
> From: "CARABAJAL PEREZ, MARCIAL ROBERTO"<mcarabajalp@ypf.com>
> Subject: [Phys-l] About black zones in screens
>
>
> Hello:
>
> I would like to ask a question to the experts in optics. We are considering the screen image  generated by a classroom projector in the case of a picture with black and white boxes, like the chess table. Are the black zones of the screen generated by absence of light (relying in an eye illusion), or they have some particular color ?. I have heard that some new LCD or LEDs TVs are using a particular light length.
>
> My best regards.
> Roberto