Hello, just wondering how I can slow down a 12 volt motor. Example a light you would see on a mail truck or plow truck that spins.

Can I simply put in a rheostat or potentiometer in line between the power supply and motor, or is there some more things I need to do.

I am building a light house( small one) and want to slow the rotation of the light down.

Any info or help would be greatly appreciated.