Four power settings, set by a magnet and a key. That is the whole idea here. The dimmer clips to the port on any Sanlight EVO panel, and the supplied key steps it through 40, 60, 80 and 100 percent. Three green LEDs show the level. Seedlings get the low end from us; the bed gets the full whack once it has grown in.
It also fakes a sunrise. Fire the timer and the light eases up over a minute or two instead of cracking on full. Young plants prefer that. Note that one dimmer drives one EVO light.