Unexpected fogging: Why is Red light failing where Yellow-Green is sufficient?

[koraks]

Yes, that's the waterproofing. If you're looking for a specification for this, these waterproof strips are generally specified as IP67, which is the common 'waterproof' rating.

 

[Letters to Theo]

Just a few words to report back.

Problem solved.

As many of you pointed out, it was the safelight — either it was too intense, or the old filter wasn't providing a suitable spectrum for Retrobrom.

Anyway, I bought an ADOX Supersafe 220 darkroom light, and my unexposed white borders came out clean.

Thanks everybody for your help.

 

[Vaughn]

Excellent. But you might wish to still do the safety test with your new lights. Most safe lights will eventually fog paper, so it’s good to know what is the upper limit of the safe safe-light exposure for your paper/developer combination. The often missed part of the test is to give the paper a very light exposure to white light to bring it just above its exposure threshold.

I would run these tests at the darkroom I maintained at the university and post the results for the students. We used fluorescent tubes with safelight filter wrapped around them. We traded a little brighter darkroom for a shorter safe time of about 4 minutes before significant fogging took place.

 

[RalphLambrecht]

Hi everyone, this is my first post here, though I’ve been a long-time reader of the forum.

I’m looking for some help regarding darkroom safelights.

I’ve never had any issues using a classic light-red safelight—until a few days ago.

I recently developed a bromide-iodide paper that came out fogged under the red light. According to the datasheet, this paper 'is routinely processed under indirect safelighting with a wavelength of 575 nm and higher; the corresponding safelight colour is yellow, though yellow-green, amber, or orange are recommended.'

Is it possible for a red lamp, which has a wavelength well beyond 575 nm, to cause such problems?

Many thanks to anyone who can share their thoughts, and best regards to everyone.

wavelength is only one factor of safelight safety. Another is light intensity; a bright red safelight will fog the paper even if it is safe according to its wavelength alone. I guess there is no hard cut off when it comes to a safe wavelength. Apparently, such a safelight still emits light of shorter wavelength. I find this confusing myselfbut from my own experience, I can say that wavelength specifications alone cannot be trusted blindly. Here is a test: take a CD and bend the reflection of the safelight and investigate such a reflection. If the safelight is really only red, we shouldn't see any blue or green rainbow colors, right? Guess what? I see those rainbow colors in all safelights I've ever inspected. That's proof to me that they emit wavelengths below red.

 

[Letters to Theo]

take a CD and bend the reflection of the safelight and investigate such a reflection

Thanks for the advice. I'll do a test, just out of curiosity.