Homebrew PCBs

--- In Homebrew_PCBs@yahoogroups.com, James <bitsyboffin@...> wrote:
> 
> I did a quick test exposure (with dry film) and interestingly the 
> wholesaler ones exposed MORE strongly, that is, the exposed areas were 
> noticeably darker, so definitely they are putting out a decent amount of 
> UV in at least a wavelength suitable to expose dry film, but I'm curious 
> as to why there would be such a large difference visibly.
> 

Your film could be responding to both the UV and blue light.   Originally, photographic film would only record blue and UV because  silver halide is basically sensitive only to those wavelengths.  As people discovered what to add to the film emulsion the sensitivity was extended, first to green and then finally adding red.  So UV/Blue sensitive emulsion is the easiest and most straight forward to make.

I'm curious about the requirement for UV light boxes as opposed to blue light boxes.  Is this due to the sensitivity of the emulsions or is it a hold over from the days when UV fluorescent tubes were available but blue tubes were not.