SuperPro 400W 120V R40 Medium Base Bulb

The SuperPro R40FL400/HG is a 400 watt, 120 volt replacement bulb in the R40 reflector shape with a standard medium screw base.

What the ratings mean

R40 describes the envelope: a wide reflector that gathers light and throws it forward, which is exactly what an underwater fixture needs to push light through the lens and out into the pool. The medium base is the same screw thread as a common household lamp, and the 400 watt, 120 volt rating puts it in the large fixture class.

Check before you order

All three numbers have to match the fixture: wattage, voltage and base. A 12 volt fixture cannot take a 120 volt lamp, and fitting a bulb above the rated wattage builds heat the housing was never designed to shed. The rating is printed inside the fixture, so read it rather than working from the old bulb alone, which may itself have been the wrong part.

Fitting

Kill the power at the breaker before opening the light. Handle the new lamp by its base, since oils from your fingers on the glass create hot spots that shorten life, and inspect the lens gasket while the fixture is open.