Yes wrote:
Yes wrote:

I posted this in the sister a.c.h newsgroup and got no reply. Hope
-- snipped --

I haven't experienced this problem before. Is it a prelude to the
monitor or video card failing? If so, which one would be the likely
suspect? What would be useful search terms to use to find out more
about it?

Thanks,

John

I did some deeper Googling and ran across a reference to "backlight"
failure. I don't know what that means, only that the symptoms I
described seem to match that term. Of course, the warranty on my
monitor expired about four months ago :-)

It would seem that the remedy is to replace the monitor, which is not a
big deal, but there was no info about how soon that you should do so
once the problem crops up. Between Paul's and Flasherly's responses,
at least I can rule out the video card. I would have hated to have to
deal with two problems at once. One at a time is more manageable.

There are two symptoms I know of, for backlight failure.

1) CCFL tubes change color when they get old. At 25,000 hours,
the light becomes brownish instead of white.

2) Inverter failures cause the CCFL tubes to go off completely.
Sometimes, the tube comes on for two seconds, then shuts off.
This means the inverter detects "too much load" when moving from
ignite to burn state. The tube operates at higher voltage and lower
current when it starts. And as it warms up, the voltage across the
tube starts to drop. The inverter and the tube characteristic are
matched to one another. But as the setup gets older, the load presented
can change enough, that the inverter no longer tolerates it. Or the
inverter just plain doesn't work right any more. There is an entire
130 page book, which discusses the quirks of CCFL lighting systems,
and its more art than science (making them work reliably).

LED based backlights are different. No nasty voltages. The LEDs still
age. Failure on LEDs is defined as the light output level dropping
below a certain level. So a user might still see light, but a LED
company person would say "all those LEDs are failed" because they
no longer deliver the amount of light expected. While the theory
says the LED based lighting should be very reliable, everyone has
seen instances of LED based lighting, where an early complete
failure happens and there is no light at all. You won't get
"brownish", or "on for two seconds, then dark" as symptoms with
LEDs. So in that respect, a LED lit monitor may have fewer
annoying symptoms over lifetime. But out-right failure (dead LED)
is still possible.

The "gray splotch" problem is probably a chemistry problem
with the chemical between the sheets of glass. Rather than a
backlight problem.

Note that, some LCD panels using LEDs, are "edge lit". They use
a fancy plastic element to redirect the light from an array
of LEDs on the edge of the panel, to cause light to appear
(uniformly) in the center of the panel. If any of the components
shift mechanically, this translates to "backlight bleed". So some
backlight bleed problems, change with time, as some of the
materials work themselves loose.

Paul