Uneven backlight - why?

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Biges

[H]ard|Gawd
Joined
Feb 28, 2008
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Why is the backlight uneven in some monitors?
(I think it is also called "backlight bleeding" if severe enough.)

I mean with the same model, same manufacturing process, one piece can have a perfect backlight, one can be horrible.

I can understand bad/dead pixels, but problems with backlight reall puzzle me.
 
Because god is testing you.

Because the manufacturing process isn't 100% perfect, why else?
 
ashmedai said:
Because god is testing you.

Because the manufacturing process isn't 100% perfect, why else?
Click to expand...

I'd like to know more technical details. Can the quality of the backlight tubes vary that much?
 
Say you've got a backlight tube. It has to light up the cavity inside the LCD such that exactly the same number of photons hits every unit area at every unit time. WTF, really hard to make. They do a reasonably good approximation considering, but it's not perfect and understandably so.
 
The other problem is all the variations in circuitry driving the CCFL backlights. Maybe LED will fix this?

As an aside: I've rarely seen an unneven laptop display, is this just because they are smaller, or is it just because they only tend to have a single CCFL (from what I've seen on various repair guides). I take it that bigger desktop panels have rows of backlights?
 
Smaller displays are MUCH easier to design and build in all aspects.
 
Thanks for the answers.
Yes, LEDs should be the answer (alhough by NEC 2690 has no cloulour bleeding problems).
 
LED BLU doesn't really solve the non-uniformity problem for two reasons:

1) It's not easy to maintain uniform brightness across a strip of LEDs. Part of the problem is that LEDs are temperature sensitive, and if the temperature varies across the panel area, LED brightness uniformity will be affected.

2) There are other causes for non-uniformity, such the the LCD panel itself, and LED doesn't fix any of those.
 
Even just the prospect of supplying uniform voltage across a large array of LEDs introduces some difficulty. If it was an easy fix to add, we would be seeing it popping up in every new display.
 
visualguy said:
LED BLU doesn't really solve the non-uniformity problem for two reasons:

1) It's not easy to maintain uniform brightness across a strip of LEDs. Part of the problem is that LEDs are temperature sensitive, and if the temperature varies across the panel area, LED brightness uniformity will be affected.

2) There are other causes for non-uniformity, such the the LCD panel itself, and LED doesn't fix any of those.
Click to expand...

From my experience of reading reviews on the LED backlighted 81F series TV from Samsung, and briefly having one myself, 1) may not be much of an issue...

However, 2) can certainly still get you...(which was my experience...)
 
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