I grew a couple recent crops with only my 400-watt HPS, did fine ... last crop, I bought one of these 'conversion' lamps, cheap enough,
Metal Halide 400 Watt Conversion
it works great, allows me to burn a MH bulb on a HPS ballast ... added bonus, for some reason, the 'conversion' MH puts out a bit more lumens than a standard MH lamp ...
as an aside, to be absolutely honest, I have seen NO difference between my high-dollar EYE Hortilux 400 vs a $9 HPS 400 replacement, so I replace bulbs frequently, since they are so cheap ...
:smokin: