What causes LCD backlight bleed?

[darren1394]

I'm interested in 22" Lcds. Does the backlight leak out from the edges and cast light on the FRONT of the screen?? Or is the light actually leaking THROUGH from the back??

 

[Captante]

Just a guess but it seems that backlight-bleed is more of an issue with cheap LCD panels (notably TN's) and may be the result of low build quality more then anything else.

 

[xtknight]

There is actually an inconsistency in the cells, causing them to lose their ability to block light. Thus, the backlight is seeping through because the cells can't block it.

 

[BernardP]

Originally posted by: xtknight
There is actually an inconsistency in the cells, causing them to lose their ability to block light. Thus, the backlight is seeping through because the cells can't block it.

But then, why is the bleed often noticeable only along the edges of the screen? I had assumed light from the fluorescent tubes is leaking due to poor sealing of the cell unit to the light unit.

 

[xtknight]

Originally posted by: BernardP

Originally posted by: xtknight
There is actually an inconsistency in the cells, causing them to lose their ability to block light. Thus, the backlight is seeping through because the cells can't block it.

But then, why is the bleed often noticeable only along the edges of the screen? I had assumed light from the fluorescent tubes is leaking due to poor sealing of the cell unit to the light unit.

Not sure really. There is probably a different amount of pressure on the panel at the edges, possibly causing problems. For example on some 20WMGX2s the pressure on the panel seems to be abnormally high causing bleeding for the first week or so. It then solves itself pretty much. Something to do with humidity/pressure but the backlight unit (BLU) didn't just magically move.

 

[Matthias99]

There's definitely some amount that leaks through the actual cells even when they're set to "black" -- you just can't make LCD cells with current tech that will be 100% opaque when 'on' and still relatively transparent when 'off'. This is why LCD panels don't give as deep blacks as emissive display technologies like CRT, DLP, plasma, or OLED.

My understanding on leaking at the edges is that it's mostly light getting around the edge of the panel. But differing pressure might affect the amount leaking through the cells as well, I guess.