I use 6 of the 27 watt bulbs in a holder that I made and use it about 2 inches from my print frame. No problems with uneven lighting and my Pt/Pd printing runs 3 to 78 minutes. I'm using Fabriano paper and some Bergger cot 320 and my Pt/Pd mix is Pd 11:1 Pt. I previously used two in reflectors for 4x5 and the exposures ran the same.