Perpendicular or Parallel?

[Big E]

I just retrofitted my 120g 48''x24x24 tank with two 400w radiums. The current hood is fairly narrow.....10 1/2'' so I'd like to create a new hood with spider reflectors to expand this. These seem to be the widest reflectors available.

Would I get better overall spread with the bulbs perpendicular or parallel? Any experiences, or is the spread about equal?

The only thing about perp is that is would be tough to add any flourescensts if I choose to use some later.

[wizardgus®]

I had checked with Ice Cap on this one and back to front is the most effective mounting for spread. Assuming you want tank center, side to side best illuminated. Now what I did (using spider reflectors) was to make the hood same size as tank, that left a few inches at the back to mount my PC reflector and bulbs. IIRC the spider mounted that way is 16". It has worked out really nice.