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Discussion Starter · #1 ·
Im curious what the ACTUAL cause of backlight bleeding is, specifically when it is only occuring around the edges, and uniformily. I took apart my Toshiba 26" to see if I could reduce some of the edge backlight bleeding. After getting the bezel off, you are left with the LCD glass screen which has a black rubber seal around the edges. It was of high quality and even all the way around. If you lift up the screen, behind it is a white panel, and behind that is the CCFL.


Doing some experimentation I first tested the CCFL and its light distribution was VERY even, and obviously not the cause of bleeding around the edges. I then did some experimenting with electrical tape adding more "seal" to the edges, but this did not have any affect on reducing the bleed.


So this leads me to my question of what actually is causing the bleed around the edges?
 

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Quote:
Originally Posted by ashenfang /forum/post/15483480


Im curious what the ACTUAL cause of backlight bleeding is, specifically when it is only occuring around the edges, and uniformily. I took apart my Toshiba 26" to see if I could reduce some of the edge backlight bleeding. After getting the bezel off, you are left with the LCD glass screen which has a black rubber seal around the edges. It was of high quality and even all the way around. If you lift up the screen, behind it is a white panel, and behind that is the CCFL.


Doing some experimentation I first tested the CCFL and its light distribution was VERY even, and obviously not the cause of bleeding around the edges. I then did some experimenting with electrical tape adding more "seal" to the edges, but this did not have any affect on reducing the bleed.


So this leads me to my question of what actually is causing the bleed around the edges?

My, you are brave



I don't know about your edge bleeding; my 52XV545U seems quite uniform and has no edge bleed. However, the 'bleeding' of the backlight as one moves off center viewing axis increases proportionately to the number of degrees off-axis that one moves. This effectively decreases the contrast ratio at the off-axis viewing locations.


This was explained to me in the Offical Toshiba XV545 Thread in post #211 on that thread as inherent in the S-IPS technology. The IPS Alpha Provectus technology used by Panasonic and Hitachi has evidently solved this phenomenon (I have the Panny TC-32LX700 and there is no dropoff as one moves off axis).


But since you have the 26-incher apart with the backlight revealed, can you measure the CRI index of that puppy to see if the dreaded 'Toshiba Green Cast' is associated with the CCFL backlight? My guess is that it is traceable to the sprectral output of the backlight and is uncorrectable. It would be interesting to be able to measure that spectral output
 

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Discussion Starter · #3 ·
My actual LCD terminology is a bit weak....what exactly do you want me to measure?


Back to topic, the bleeding occurs looking at the TV head on or at an angle, and only in the edges, and only annoying on black or dark screens. I know that LCD's cannot block all light, but its interesting that the most (98%) of the screen can block light, except at the edges, with no indication as to why....?
 

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I personally think that the edge flashlighting is caused by the bezel pinching the panel,making it bend or flex slightly-seeing as a lot of the threads on this forum mention loosening off the torque on the bezel screws to reduce flashlighting.

It's only a guess though,I'm not sure if this is the actual cause.
 

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Discussion Starter · #5 ·
thats what I was thinking too, but when the bezel was off and the glass was "free floating" on the CCFL backing, the edge bleeding was still the same as it was with everything together, which is why I ask the question, where is it coming from?
 

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I'm stupid on the matter, but if I had to guess out of nowhere..........


........I would think that around the edges of the TV, light reflects off the edge side as it has nowhere else to go unlike in the middle where it is merely uniform on all sides. At the edges, the light permeates outwards all around it including the side, causing a reflection and more intense light around the edges. That's just a total guess.


I do however understand the screen not being completely flat as well. If I remember correctly, there were some pics of somebody taking their LCD apart and under the visually seen screen, is the thin white screen below it and in between the main screen and the backlighting of the unit. If that thin white screen wasn't entirely flat, I would think off of Snell's Law(???) or whichever law of physics deals with the angles of light refraction/reflection, that the non-uniform screen would cause the backlighting to pass through at different angles causing the problem.
 
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