The standard incandescent model. I heard that it takes the 5 1/2 D cell rechargeable battery, similar to Mag Charger. This battery is very close to the dimensions of 3 D batteries, correct me if I am wrong. I also heard that it (at least the earlier versions) use a PR type bulb. What I want to do is find a used, earlier model of one of the SL-20 and run it off 3 D batteries and a 3 D Magnum Star Xenon bulb. Any input would be appreciated.