"Bob F" wrote in message
"3v LED" suggests LEDs with built in resisters. Remember LEDs
are polarized - if you connect them backwards, they won't light.
2 3v LEDs in series should work fine off of 6V. Do that twice for
4 bulbs.

Oops - I missed the 2 C batteries. Just parallel the 4 LEDs to the 2 cell
in series.