If you can lay your hands on one or more of these red (~630nm) OptiLED Festival S11 bulbs*, then cover and allow it to shine through a single sheet of Rubylith, you will have a DIY safelight that will not fog Ilford Multigrade IV FB or RC paper for at least one hour.

I know, because that's what I use (six of them on a strip under a curved sheet of Rubylith) and I've done the preflashed safelight fog test using this combination. I stopped the testing at 60 minutes with absolutely no sign whatsoever of paper fogging, even when tested using a reflection densitometer to confirm what my eyes were telling me.

The Rubylith acts as a cutoff filter and is required to suppress a tiny sliver of blue light also emitted by the unfiltered bulb. Its effect on the red output is negligible. Suppressing that small blue component is what gives the insanely long fog test results.


* Or what I believe may be the higher-powered successor OptiLED Festival H13-VF bulbs. Or any other bulb using the same basic red LED element.