it is a conversion bulb. i bought the setup on ebay from htg supply (link) 400w BOTH HPS+MH GROW LIGHT 400 watt Sodium and Halide! - (eBay item 180099389036 end time Oct-18-07 06:48:02 PDT)
tell me if you see any safety hazards with it, i am using all the stuff that came with it bulbs timers...