Good question...but unfortunatley I do not know the answer.

I almost bought the frosted one myself but opted for clear.

I cannot for the life of me see a reason white a diffused MH light would be bad or harmful or not work. Especially at 1K W.

Wait for some other opinions....

Thanks for posting here, maybe we can all learn from this question
HARDDON Reviewed by HARDDON on . q on metal hallide i have been using an 1000w hps for a couple of years.my first MH just arrived but i may have orderd the wrong one.it is coated not clear,i can exchange it no problem, just wondering if it matters coated or clear. thx for any responce. Rating: 5