WTB Cheap safelight
A really bad safelight could pass that test. Emulsions have a threshold exposure below which they are not sensitive but once it is exceeded then tiny amounts of additional exposure that wouldn't have exceeded the threshold will cause further density. The symptoms will be fogged (not always obvious except by comparison to a print done in darkness) highlights while borders are still white. Preflash your test paper with no negative in the enlarger for a light gray overall (about zone VII to VIII in zone terms) then use that method.
Originally Posted by John&Tessa
Cheapest and safest option is to get a $3 red LED tail light for a bicycle off the internet. You can also wire up a string of ultra-bright red LEDs to a wall-wart if you're feeling DIYish.
Filtering a dim incandescent bulb with rubylith will work, but a better option is to use LEDs that don't emit the problematic wavelengths at all.
Most of them do emit, at least some. But I agree that LEDs can usually be brighter than filtered incandescents and still be safe.