Hi,
Iwasaki 250w used by reefers are known as MV conversion lamps. They are MH lamps, but they are design to operate on a MV fixture. MV are cheaper because they don't need a capacitor to start.
http://www.rpi.edu/dept/union/aquari...ml/DIY_MH.html
Iwasaki is more blue when MV ballast is used.
- Victor.