"Tunnel Vision" is a defect in early B&W/Grayscale Active-Matrix LCD displays. Displays affected by this issue will slowly develop a black viginnete effect around the corners of the display, getting worse the longer it has been running for. The effect is only visible after the LCD has been running for a certain amount of time, which can vary on different LCDs. After the display is left off for a few hours, it will have disappeared, but will reappear again as the display is used again.
The issue can be bad enough that it starts appearing after only a few seconds, and will envelop nearly the entire display within minutes, or as mild as only having only the corners darken after running for several hours. How severe the effect is different on each panel.
It would appear that nearly every one of these LCDs is currently affected to some degree. Finding one with no Tunnel Vision is now extremely rare. Strangely, the LCDs used in the Macintosh Portable do not suffer from this defect nearly as much. They can still get it, but seemingly much less frequently than other panels.
Tunnel Vision on different displays can be slightly different. A perfect example of this is how the darkened areas look. For some people, the darkened areas will appear black, with nothing visible. For others, the image in the affected areas will simply display with inverted colors.
Some people report seeing areas like the Mac OS menubar appearing "burned-in" after the display is shut off, which is strange for an LCD panel.
The true cause behind tunnel vision is as of yet unconfirmed. The most likely theory is moisture ingress between the layers of the screen causing some funkiness in the liquid crystal, caused by a defective seal between the layers of the screen. This theory is the most commonly accepted, and it is well supported by the evidence we have on fixes. However, alternatives have been suggested as well. Another idea is simply that the defective sealing itself is the cause. We don't have any way of conclusively proving either, but we do have some proven fixes.
Yes and no. The most common method people use to fix these panels is to bake them in an oven at 100 degrees celsius for a few hours. The idea here is to boil out any moisture, while not being hot enough to cause damage to the LCD's polarizer film or other components. Proponents of the defective seal theory theorize that the baking instead "reflows" the adhesive. I could honestly believe either, and we honestly don't know for sure which is fixing it. What we do know though is that baking below 100 degrees doesn't work well, and baking over can cause damage.
This fix has shown good results in the short to medium term on some displays. We can't call it a cure though for two reasons.
If you have a severe case however, there really isn't much to loose. One idea I have to lower chances of damage would be to avoid baking sessions longer than 4-5 hours. 4-5 is usually enough to improve things for moderate/light cases, so perhaps avoiding long 8 hour sessions could reduce the chances of damage for severe cases. This is all unproven though.
Overall, the oven method works about the best of any people have tried. It doesn't always fix panels 100%, but complete fixes have been done successfully.
Other suggested fix methods have been to try leaving the LCD out in the hot sun, using a vacuum pump, or leaving the LCD submerged in silica gel for a long period of time. Some have claimed these methods to be partially or potentially effective, but seemingly less so than baking.
Luckily, these LCDs are quite rare and were only found in a few laptop models. Specifically, the Apple PowerBook 170, 180, Duo 250, Duo 280, 540, the Macintosh Portable, and a select few Compaq laptops (LTE Lite and Elite models ending in "E").
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