[Patrick]

3 or 4 times in the last few days, I've noticed a problem where part of my iMac's LCD suddenly goes dim when I'm using it. Unlike the screen's automatic dimming feature, this occurs as a gradient, with the darkest portion at the top and normal brightness toward the bottom. After restarting, the problem goes away. I don't know enough to guess whether it's a hardware or software issue, but when it happens I notice that I can't activate the screensaver in the usual way. Using OS X 10.58, on a 1.8 GHz G5 (rev. A) with 512 MB RAM here.

I'm half wondering if my computer's days are numbered. The internal HD failed a couple weeks ago (though 6 years ain't bad, I suppose), and I'm surviving on an external drive at the moment. Could replace it, but the LCD thing makes me wonder if there's another hardware issue at work here.

[P]

This sounds like the backlight of the LCD is going. I have that exact model, I liked it a lot and it still sees some use as an emergency TV, but it's time to upgrade.

[seanc]

Sounds like the CCFL (bulb) at the top, or the connection to the bulb is failing.

[Patrick]

Thanks. So I just googled "imac ccfl gradient," and sure enough, found people describing the same problem. Upgrade time… I remember drooling over those newer iMacs anyway. Here's to hoping I'm on Santa's "nice" list this year.

EDIT: apparently the screensaver thing wasn't part of the problem. I just remembered I'd zapped the PRAM a few days ago, which would have reset certain system preferences like the screensaver hot corner.