I think I'm starting to understand.
Back to my original question. Can a DC DC buck step down suggested in the early answers be used with such a powerful power supply?
I'm asking because I have today 5m, but this is not enough for the final project I need. Could I use that mini converter with a power supply of 100w (12V) or more?
Also, I still don't know how to calculate resistance and current to control the lights with an Arduino