Q: PowerBook G4 with 10.5.8

Has it been turned off via F8 key?

F8 toggle on/off, F9 decrease, F10 increase.

Important: Even when the keyboard illumination feature is on, the keyboard illuminates only in low-light situations.

You can turn off the keyboard illumination feature in the Keyboard & Mouse pane of System Preferences or by pressing the F8 key.

The second paragraph suggests that there is a preferences file somewhere that may need to be trashed.

This may be wide of the mark but was your upgrade from an earlier version of OSX (i.e. pre-10.5) or was it an incremental update from an earlier version of 10.5? If it was the former - say from 10.4 - did you use a full retail disc? If by any chance you used a grey install disc intended for another machine there is always the possibility of anomalies. As I said this may be an irrelevance - just refining the possibilities at this stage!

Very strange. As an aside I didn't know you could still buy Leopard from an Apple retail store - I thought you had to request it direct from Apple, but maybe its different in Hong Kong.....

Anyway something has certainly gone wrong. I moved my PB (1.25GHz) from 10.4 to 10.5 without any consequence as far as the illuminated keyboard was concerned so you have been unlucky. When I look at the keyboard preferences pane underneath the section about the F keys I have another check box relating to illuminating the keyboard. My MacBook - which doesn't have the illuminated keyboard - shows a preference pane like yours. Clearly in your case the system isn't recognising that the computer has this function. All I can suggest is that you try reinstalling.

Same problem.  I have been trying on and off to solve for a few years.  Reinstalled Tiger, reinstalled Leopard, took powerbook apart to check connections to keyboard and lamp, etc, etc.

Then, on the off chance, I was googlng the problem and came across this old Apple help file.

http://support.apple.com/kb/TA27062?viewlocale=en_US

It worked - I don't quite understand why but unless you are in a dark environment the features are all disabled; covering the speaker grills where the light sensor is located seems to work with the screen dimming feature but not the illuminated keyboard.

Took my G4PowerBook into a dark room and the illumination feature worked - I could make all the adjustments using the F8, F9 and F10 keys and it stayed working.

Very strange.

I thought that was taken as read!

The mystery is that the "illuminate keyboard in low light conditions" checkbox just isn't there for the OP.

It doesn't come and go depending on the ambient lighting - I've just checked - full sun here and there it is.

Obviously somehow affected PB's don't "know" that they have illuminated keyboards. They'll all be dead soon anyway so its only of academic interest.

Well Braby

You are right about the checkbox. I've been trying to solve this not-very-important issue for quite a while, but, when I took my PowerBook into a dark room the feature that hadn't been working started to work again.

My PowerBook is still a trusty workhorse, I only sold an old Performa a year ago, and it's very satisfying to keep old stuff going even while enjoying using the new kit.

What puzzled me is that trying to fool the system by covering the sensor grills didn't work, being in a dark room did, the feature switched itself back on???

That is certainly a mystery. Glad you're still enjoying using your PB. Mine makes an occasional guest appearance! Even my MacBook is no longer the workhorse it was - those iPads have a lot to answer for!