A circuit with a dimmer is useful for incandescent safelights. Additionally, this can greatly extend the life of the lamps.
Dimming a household incandescant bulb, safes electrical energy and prolonges the lamp longevity (which already is about 1000h) and makes filtration easier, without loosing too much red radiation.
It could be though that ready-made incandescant red safelight lamps for this reason were designed to run underrated. I never checked that.

