screw head i'm not veri sure..but i bought a fitting light bulb to test the fixture and its written e27 on the cover...it's best u check with the other par38 user or aquarium artist..i think the light is strong enough,but the angle is abit tight...the sides seems abit dark,but i did keep a monti for fun (1 mth already) and still surviving, no change in colour but the colour like abit brown,dunnoe whether is the original colour.i post a pic later. my water parameter is abit off at the moment so of the coral ain't doing well but for those zoas that are doing fine,the colour seems to be more intense than b4...dun noe is placebo effect or not..
if u got the budget , go for par38! the shimmer is simply amazing...u wun regret it!