Hi, I want to build a simple light box to have a go at some alternative processes. Living as I do in the UK natural light is a bit... unpredictable :rolleyes: I am starting off with simple cyanotypes and salt prints. This has been quite succesful, but I'd like a bit more consistancy and control. I am lucky enough to have a laser power meter which measures light intensity at various wavelengths, so I can meter up various types of UV light sources and also measure the light passed or absorbed by various diffusers, which should make life a lot easier. There is are obviously a lot of different sources of UV available for different purposes. The tubes used in sunbeds are quite different to the ones I use in my fishpond water purifier - and both are very different to a Disco 'Black Light' effect. But... can anyone tell me which wavelengths or range of wavelengths we are looking for? Sunlight obviously contains a wide mix which will change depending on latitude, time of day, condition of the sky. I have already discovered that the amount of clouds in the sky can affect contrast. I haven't yet found any information on sensitivity of alternative photo chemical processes that discusses specific wavelengths, though. Can anyone point me to any information on this? Thanks.