Thought I'd post DIY LED safelight "Mark II" as it was a fun little project.
It takes 8"x10" filters. Shown is a Kodak #1. Note I used Kodak filters because I was able to get a few recently for a song. Otherwise they are ridiculously expensive so you'd be better off with some Rosco or Lee gels or something.
The pictures show the safelight with the red LED board installed. I would use either a Kodak #1 or #2 for ortho film (masking). The #1 works well for printing too. But I still tend to prefer the good old Kodak OC for printing so I made an identical LED board with warm white LEDs. I can slide that one in and use a Kodak OC filter.
The "electrical work" for this is essentially plug-and-play for dummies from Superbrightleds.
The dimmer works by "pulse width modulation" so that spectral output is constant regardless of dimmer level.
These LED safelights are fun projects but as others have noted, always do proper safelight tests. These cheap red LEDs are not as sharp cutting as one might expect, nor do these particular red LEDs peak far enough into the red spectrum as I'd like. Superbrightleds does offer another red that peaks at 660nm with a fairly narrow band, but they are not plug-and-play (require soldering etc) so I didn't bother. Since I had the Kodak filters anyway, putting a #1 or #2 over red LEDs makes for very long safe times.