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Changing the Backlight and now new greenish problem
Posted: Mon Feb 11, 2008 10:34 am
by beeblebrox
The T20 I was given to fix has a dim and yellowish display (Samsung LTN 141X8). I remember that it was bright white when I bought it 3 years ago.
Now, I changed the CCFL with a brand new one (Ultra bright white 7400Kelvin ). Unfortunately I have a greenish tint now.
Does it mean that the CCFL is bad (production error) or that the LCD has a yellow tint (polarizer plastic decayed) which in the end would give me green?
Did anyone have the same problems? I did not find any other thread on this topic
( Hint: Blueish CCFL + yellowish LCD = greenish tint -> really Ogrish.)
Posted: Mon Feb 11, 2008 10:12 pm
by ajkula66
The only way to find out for sure would be to throw in a different CCFL, but I'm fairly certain you don't feel like doing that...
I'd be placing my bet on your "ogre" sandwich due to deteriorating LCD condition...
A very interesting one indeed. Keep us informed...
Posted: Tue Feb 12, 2008 7:14 am
by beeblebrox
ajkula66 wrote:The only way to find out for sure would be to throw in a different CCFL, but I'm fairly certain you don't feel like doing that...
I'd be placing my bet on your "ogre" sandwich due to deteriorating LCD condition...
A very interesting one indeed. Keep us informed...
Yes, I checked the CCFL without notebook connection. It is fine, very bright and white. Putting it into the LCD it is quite dark und greenish. Yuck...
After reading some threads on other internet forums I got the following theory:
Backlights dim after some time (1-3 years) because their phosphorous layers decay. These layers are bombarded by UV rays from the mercury atoms and they render UV rays into visible light at different wave lengths. When these layers decay, the lamp dims and is more transparent for UV light, which then goes thru all the plastic foils (polarisers and diffusers). Just like plastic turns yellowish in the sun's bright UV light, these plastic layers decay giving a yellowish tint. You can see that e.g. on iMacs, iBooks, Macbooks and Mac Minis, who are exposed in a sunny office.
With a new lamp you have a fresh new bluish tint (7500-8400 Kelvin). Bluish tint and yellowish tint gives exactly: greenish tint.
So, according to this theory is is better and cheaper to replace the CCFL every 1-2 years (and dump them cheaply on fleabay
.
A new LCD costs around $100-200. A new CCFL is about $15.
Way to go...?