Shield the Metal Halide or no ?

[B]

I'm about to upgrade from PC to Metal Halide lighting and
have been told both TO and NOT TO place either a glass or
acrylic shield or cover between the MH and the aquarium
water surface. It's about 10 inches from the water surface
to the MH bulb.

What do experienced MH lighting reefers reccommend ?

TIA
B

[Rod]

Single ended, no shield. double ended, use a shield.