PB sleep light question.

I recently began using our newly purchased 15" 1.67 GHz PowerBook, and I have a question about the sleep light. On my iBook, the light would only illuminate and pulsate when the computer was "sleeping". I have discovered that on the PowerBook, when I set the display to sleep after 10 minutes (leaving the rest of the computer "awake") the light illuminates and pulses just as if the entire computer were sleeping. I'm curious if this is something unique to the PB or if my sleep light is somehow malfunctioning. Can anyone who owns a similar PB describe how his/her sleep light functions when the display sleeps? Thanks in advance.