If you look at the PAR of a 250W Iwasaki vs a 250W Radium on Joe Burgers MH test site you will see that the Iwasaki has about twice the PAR of the Radium for most ballasts. So a 400W radium is probably close to the 250W Iwasaki assuming you will get about 1.6 times the output extrapolating from the 250 Radium to the 400W Radium. The Iwasaki may still be higher with most ballasts.
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