How many LED's are in a typical LED monitor?

[patjk]

How many LED's are in a typical LED monitor? For example, how many in a 20in vs. in a 24in, etc?

Thanks

 

[mgb_phys]

LEDs are only used as a backlight, not as individual pixels.
There are two arrangments - a grid of several hundred LEDs in the back of the TV and for thinner units a line of a few dozen LEDs along the edges.

 

[patjk]

Great, thanks.

What in a LED monitor causes the colors to appear?

Cheers.

 

[mgb_phys]

In an LCD monitor individual pixels are covered with a red/green or blue coloured filter made of plastic. Each pixel contains an LCD shutter which either let's through or blocks the white light from the white LEDs in the back. An individual pixel then gives a red/green or blue point.

Plasma TVs are similar except that each pixel glows white, rather than needing a backlight, the color is still set by the filter in front.

 

[patjk]

Great info, thanks.

Do LED monitors use the same type of setup as an LCD (as you discussed above)?

For LCD, can 1 pixel put out more than 1 color (like a gradient for example. I assume not, but curious if so)? And how are each pixel lit (what provides the light source, is it just a small bulb?)?

 

[mgb_phys]

For an LCD TV the backlight LED gives you the ligth source - the only reason for using LEDs rather than flourescent lamps is the smaller size, greater efficency and longer life.

A single pixel only puts out one color (red,gree or blue) groups of three or four pixels are used to give all the colors by varying amounts of these primary colors.

ps .There are purely LED display screens used for large outdoors screen such as in stadiums - these do use groups of LEDs in each pixel to give either a red, green or blue light.

 

[patjk]

How does the computer trigger what color needs to be shown in which location at any given time?

 

[mgb_phys]

You set a voltage on a line that turns on or off the LCD to allow light through or not. You can control the brightness by turning the LCD on/off quickly and varying the relative amount of on-off time.

see http://en.wikipedia.org/wiki/Liquid_crystal_display

 

[MATLABdude]

There are also Organic LED displays in which every pixel actually *is* an OLED (okay, 3--one each for red, green and blue in the colour displays and one in the monochrome ones).
http://en.wikipedia.org/wiki/Organic_LED

While I've heard of them in small cellphones and handheld devices, and the Wikipedia article mentions that there is at least one commercial OLED TV, I don't think they've really taken off (or at least, not yet).

 

[minger]

the only reason for using LEDs rather than flourescent lamps is the smaller size, greater efficency and longer life..

Also note that some of the newer/more expensive LED-LCD employ a technique called local dimming, where certain of the backlighting is turned off so darker blacks and higher contrast ratios can be displayed. Note that the vast majority do not though.