Starting with the PowerBook G4 Double-Layer SD models, the sleep indicator light in the lid button has a new behavior.
When you first press the power button to turn on the PowerBook G4, the sleep indicator will also turn on. As the computer starts up, the indicator stays on until the display turns on.
After startup, after the system shuts down the video circuit (the screen goes dark) but before power is shut down to the main logic board, the sleep indicator light will once again turn on solid. It will turn off if the video is turned back on or it will start pulsing if the computer meets the condition for sleep.
You can use this light as a diagnostic visual to determine whether the computer is getting power at startup.