I used three button cells from a light up bouncy ball to power the high intensity blue LED. Then I hot glued the batteries to the inside of the cap.
I soldered a small push button membrane switch between the batteries and the LED. I glued this on the right side of the inside of the cap.
I unfolded the fabric at the very front of the cap and cut a small hole just big enough for the led to stick through. I hid all the wires underneath the fabric and reatached the fabric back to the card board with hotglue.
To turn on the LED I just put my hand up to the side of my cap and push. Origonally I wanted the swith to be in my gown sleeve, but I had no way of hidding the wire going from the cap to the gown. If I had long hair I could have pulled it off.
The LED is hardly noticable until i press the button.