Today I happened to look at the TV while it was off and noticed that its screen was reflecting glare from one of the windows in the room. There was a striation pattern in the reflected glare! I was able to capture it on my digital camera.
The glare-striations are not in the glare light itself. They stay still on the screen when I move my head slightly so as to reposition the glare "hot spot" with respect to the borders of the screen.
Although I can't really match the two banding patterns striation for striation, I'm convinced these two phenomena are actually one! That is, whatever causes the window glare to be non-uniform in its reflection from the screen is also what causes light from the LCD panel, when it is on, to be non-uniform in its distribution.
Why do I think this? Both patterns of non-uniformity involve vertical bands (striations) of various arbitrary widths. The widths are all fairly broad, on the order of an inch or so. They don't seem to appear on either end of the screen, just in the middle 50% or so. There are no horizontal striations, just vertical ones. The striations are quite faint in both cases. Their "edges" are indistinct and gradual in both.
The glare-striations are clearly not produced by the TV's electronics, since the TV is off. They are not due to backlight non-uniformity or leakage through the LCD panel, since there is no backlighting.
What exactly does produce them is hard to say. My best guess is that it's something physical, or mechanical, or geometric — whatever word you want to use for something not perfectly smooth and flat. Possibly the front, outer surface of the LCD panel is rippled. I notice that when I apply light finger pressure (using a tissue), the front surface gives a bit.
Or possibly the ripples are in a deeper layer of the LCD "sandwich."
An LCD panel in an HDTV is made of several layers, the first one (counting from the rear forward) being the backlight. The backlight simply produces light, which then passes through a vertical polarizing filter (the next layer) that polarizes it — makes sure all the light waves are aligned in one direction, the vertical one.
The comes the liquid crystal layer, sandwiched between two glass plates whose grooves cause the intervening sequence of liquid crystal molecules to be helically twisted in alignment. The light passing through the liquid crystal layer has its polarity twisted because the liquid crystal molecules are themselves thus arranged. So the light from the backlight will be able to pass right on through the next layer, a horizontal polarizing filter ... and the pixel will light up.
The color of the pixel — red, green, or blue — is produced by a tiny colored filter in the light path. The colored filters are yet another layer of the LCD sandwich.
The first glass plate in the sandwich houses an array of electrodes, one electrode for each pixel. Each electrode contains a transistor. If any given pixel's transistor has voltage applied to it, it will untwist the liquid crystal material in proportion to the applied voltage. The higher the voltage, the more the crystal untwists.
The result is that less of the light passing through the liquid crystal will be able to penetrate the horizontal polarizing filter. The pixel will darken.
If the maximum voltage is applied to the transistor for a given pixel, the liquid crystal will be fully untwisted, and the pixel will be black (or, at least, it will be as dark as it can be).
But if the liquid crystal "leaks," the pixel won't get that dark. It leaks when:
- the applied voltage is too low
- the appropriate maximum voltage doesn't fully untwist the liquid crystal
- there are impurities in the liquid crystal
- there are defects in the alignment of the various parts
The problem I have — vertical striations — could however be related to defects in the mechanical alignment of things on the various inner layers of the LCD sandwich, such that when light enters the panel from the front (as with the window glare) it is not reflected back evenly.
I have had not one but two LCD panels in my Sony: the original one and a replacement panel installed by an authorized technician after I complained of the striations. As far as I can tell, nothing whatsoever changed when the replacement panel was put in.
To my eye, that is, the exact same striations beset the second panel as beset the first. They appear to be in precisely the same locations on the screen. It is enough to make me wonder if they might be the result of physical irregularities in the front frame of the TV, against which the edges of the LCD panel are pressed when the necessary screws are tightened during assembly of the TV. If so, a replacement panel would be distorted in the same way as the original was distorted.
So that's where I stand on the striations issue at present. I am becoming convinced that there are mechanical distortions in the LCD panel which cause them to show up in pictures being produced on the screen and in glare reflected from the screen.