You need 1N4001 diodes rated at 1amp, they have a forward biased voltage drop of .7 volts, just use as many you like in series to get the required output for a 6volt battery,fixit wrote:I can't find any .7 volt Zener diodes.
Maybe if I go to a 12.6 volt battery, I can find one that will reduce down to 4.5 volts.
It's a bit like adding extra LED's to your lights, thus increasing there voltage requirement.
Anyway I'd personally try that myself first, if you use a voltage regulator it will dump the excess as heat, not what you want to do if using batteries.
Another way is a pulsewidth modulating power supply to control the mark/space ratio, that would allow the brightness to be controlled.