Not sure but this might be of interest. It's a fun little project. I have since built a new "Mark II" version which contains both red and white LEDs, and accepts Kodak safelight filters. So I can either run it uncovered with the red LEDs on for excellent safe times with paper, or if I'm working with ortho films for masking, I can slide in a #1 or even #2 Kodak safelight filter and use the white LEDs.