Originally Posted by Steve Smith
I'm fairly sure it's a relay. In a thread on another forum, I raised the issue of using a solid state relay module for a timer and Richard of RH Designs stated that he uses mechanical relays.
It was a few years ago and I don't know if that is the case with all of his products but I suspect that it is.
Presuming that to be true, there will be zero issues using a Stop Clock with an LED enlarger and/or safelights.
Analogue Photography and Film FAQ
Open-Source F/Stop Timer