Flashing light

Alright, so I looked through the archives and I didn't feel like I found a tutorial that helped me out. I'm trying to make an icon out of this picture:







And I want to animate the light on his head so that it flashes (I'm using the big picture instead of the icon so you can kind of see the light better). And I'm not quite sure how to do it. I'm using Image Ready.

Thanks!