I was using my MacBook today when suddenly the backlight turned off, right while I was in the middle of using it. I know it was the backlight because:
- I have an external display, which remained on, and I could still see my desktop (so the computer hadn't turned off)
- The windows that were on the internal display didn't move over to the external display, meaning that the internal display itself was still on, but just not illuminated
After some experimentation, I discovered that I could get the backlight to turn back on by holding down F1 (to lower the brightness) until the brightness setting reached 0, then holding F2 (to raise the brightness) until it was back at 100%. It was as if the system didn't "know" that the backlight was off until I manually lowered the brightness to 0, and then it would know to turn it back on when I raised the brightness.
However, after doing this, the backlight would only last for a few seconds at 100% and then it would turn off again.
Finally, I tried raising the brightness slowly from 0, and was able to work my way back up to 100% without it turning off. It's been working since.
Is this a hardware failure or a software glitch? I'm running OS X Mountain Lion (10.8.4) and the issue persisted through a reboot.