I have a 400 watt MH balast that was made. I was told to use Ushio bulbs with it. But I can't find any 6500K bulbs in Ushio. So can I change the bulbs and use the Iwasaki bulbs? I know that might be a hard question to answer. But with the ballast being built I can't give any more info. So does anyone know if these 2 bulbs are interchangable?