[Updated]

Apple Released iMac G5 Sleep Light Update--Mystery Updater: If you have an iMac G5, the updater may appear in the System Preferences Software Update pane or it may not. No standalone updater is available at this time [11:30am EDT]. According to the Read Me file,

The iMac G5 Sleep Light Update adjusts the brightness of your iMac G5 sleep indicator light so it's not as bright during the evening. The daytime brightness remains the same.

This update is installed in Applications > Utilities and should automatically launch. Click Update and follow the onscreen instructions to apply the update.

Note: Once the update has started, do not cancel or interrupt it. The updater takes over one minute to complete. During the update, your computer fans will run at full speed, but will return to normal once the update completes.

It is not clear for which iMac G5 model the update is intended. The updater appeared in the Sofware Update preference pane of our early 1st generation 20" iMac G5 but not in our recent 2nd generation 20" iMac G5. Still, it would not launch and run on our 1st generation iMac G5. [Update: We checked Software Update again on our 1st generation iMac G5 and the update was offered again. This time a restart was required and it updated our firmware. Also, Charles Williams wrote that the updater worked on his 1st generation 17" iMac G5. Mystery solved.] [Dana Baggett & Bill Fox]