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

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.

Most modern papers are safe under amber safelights, a few of the older papers are safe only with red. Slavich was safe under red and fogged under amber. So yes it is possible for a red safe to fog some papers. But filter need to be replaced, as filters age you need a weaker bulb. I think my Foma FB is safe with both amber and red. Are you using a new to you paper, or it this happening with a paper that you have processed under red in the recent past? If so the problem might with your safelight, the filter might need to be placaed or you could have small white light leak. You should also check to see if your enalrger has developerd a light leak that is being reflected on to the paper when being exposed.

Oh, forgot to ask, have tested your paper? Cut a strip in total darkness, put in developer for at least 2 to 3 minutes, then stop and fix as usual. Should be paper base white.