Teach your baby the sign for the word light in baby sign language with the following description and video.
Form the hand into a fist. Flick the fingernail of the middle finger against the side of the chin three times.
ASL Pro: http://www.aslpro.com/cgi-bin/aslpro/aslpro.cgi
Signing Savvy: http://www.signingsavvy.com/