I have a 16V 8W bottle dynamo and two light bulbs:
- one is marked 6V 0.05A and is working properly
- other does not have any inscription and ceased to work.
I would like to replace the second light bulb. What should I search for?
Apparently the 1970s PX-60 (see the OP's comment had a Soubitez bottle dynamo ("génératrice") on the rear wheel as sold. Similar looking vintage Soubitez dynamos come up on eBay, where sellers and photos both indicate that they're 6V 3W.
However dynamos labelled 16V 8W really did exist: They were made by Sankyo, and again appear on eBay. They were apparently fitted to Raleighs and Schwinns in the 70s. If that's really what the OP has, and the output is really that much higher rather than just being an optimistic rating, I could be tempted to try something like a 12V 5-6W incandescent bulb in the front, and 12V 1W at the back, if you can somehow make them fit. These are cheap as they're used in cars, so getting a couple for testing would be reasonable, as would getting through them quicker than you'd really like.
I just went to the chinese shop and randomly bought a cheap lamp that fits that socket. It says 3.6V 0.75A. It seems to work fine, but I still haven't tried it at very high speeds. It is not likely to last long - just as the other light I have. I'll try to turn off the lights when going very fast.
When it stops working I will look at this in order to choose the light bulb: https://en.wikipedia.org/wiki/Series_and_parallel_circuits
Apparently I should invest in 16V light bulbs, since that for parallel circuits the potential difference (Volts) is the same for all resistors.
As for the current, it should be calculated as such:
The current in each individual resistor is found by Ohm's law. Factoring out the voltage we get:
Itotal = V(1/R1 + 1/R2 + 1/Rn)