81 XT 500 headlight question

[Geotraveller]

Mate of mine here in NZ has been restoring a 1981 XT 500. He has run into an issue with his headlight bulbs. The battery on the bike is 6V and the circuit is good. But a 6V bulb blows. He tried a 12V bulb, that works but is very dim.

Any ideas please?

 

[gastank]

 

[Geotraveller]