LCD Panel/Screen and Backlight Question..?..

[MisterD]

Question: If the backlights are working and the LCD Panel is not doing anything, does it still let the backlight shine through to form a white or grayish screen? in other words does the LCD Sceen have to be working in order to see anything such as a white display with no picture? or is that just the backlight you see on the screen?

[budm]

Re: LCD Panel/Screen and Backlight Question..?..

http://s807.photobucket.com/albums/y...t=DSCF1912.jpg

[MisterD]

Re: LCD Panel/Screen and Backlight Question..?..

Here's some information I found on the web.

Unlike older cathode ray tube (CRT) displays that scan an electron beam over a phosphor screen to create light, LCD displays are composed of a fixed grid of tricolor pixels that change transparency based on a range of voltage levels provided by the monitor's controller. Without a voltage the pixel is opaque and blocks the screen's backlight from transferring through it, and when a full voltage is applied then the pixel allows full transmittance of the backlight. When this is done over the entire pixel grid in patterns, then you see those patterns on the screen.
At a very basic level, the way pixels work is a voltage change alters the pixel to allow more or less light through. When there is no voltage, no light is let through (darker), and when the voltage is at its maximum level then 100 percent of the light is allowed to pass through (brighter). By supplying intermediate voltages the computer adjusts the pixel's transmittance levels for its three color components, to display various combined colors and intensities.
This pixel-based setup for LCD monitors provides many advantages over CRT displays, but does have potential drawbacks arising from the fact that the image is dependent on millions of independent electrical components as opposed to a single scanning beam, so if faults occur in these components then the display output can be affected. The resulting problems include stuck or dead pixels, as well as a residual image effect.

[budm]

Re: LCD Panel/Screen and Backlight Question..?..

In liquid crystal displays (LCDs), use is made of linear polarisers, familiar to most as the glass in polarising sunglasses. If you “cross” two polarisers (i.e. arrange them at 90 degrees to each other) then light does not pass through. This is the basis of the LCD, but between the cross polars the liquid crystals are arranged with a “twist”. This twist allows light to pass through. However, when an electric field is passed through the liquid crystals, the twist is removed, and so light cannot pass through – the area appears black.

For more info on liquid crystals, see my previous answer at:
http://www.physlink.com/Education/AskExperts/ae303.cfm