JAustin;421537 wrote: you don't need an HQI ballast to start them, you need a pulse start magnetic or any electronic. The 250w SI MH bulbs are designed to run around 300W so they need HQI for best performnace. The 400W Radium is designed to run at 360W so it runs best on dimmable electronic. However; if you run the 400W Radium at 400W+ it's one kick butt 20K that out performs most 400W bulbs of any spectrum but will last about 6-8 months before it needs to be changed.
The 250W on HQI lasts almost a year even being overdriven.
HTH