Shut off the light fixture and turn off the power supply to the light fixture if possible. Spray the light fixture lightly with a spray-on, all-purpose metal cleanser. Wipe it down with a soft cloth.
Rub a 100-grit sanding block back and forth against the brass surface. Repeat with a 220-grit block. Wipe down the brass fixture with a tack cloth to remove the dust from sanding.
Arrange newspapers around the wall next to the light fixture and tape them in place with painter's tape. Tape off any parts of the light fixture that you don't wish to paint.
Spray the light fixture with a light coat of metal primer. Allow it to dry overnight. Spray it with a light coat of chrome-colored spray paint. Allow it to dry for 12 hours and then apply a second coat, also allowing it to dry for the same amount of time.