Look for a "police lights" app that has source code available. Those are apps that make the LED alternately blink red and blue. Note; do NOT use anwhere a police officer will see you using it, especially in a vehicle on the road.
Also google for programmatic control of notification LED for Android.
I dont think you understood my question, what I meant was how can i get this LED notification light to turn on for Google + for example, or even Gtalk.... I dont want "cop lights"