The three-step function is a technique that makes it possible to dim an existing installation. This type of light source cannot be serviced by a normal dimmer switch.

The smart thing about the three-step light sources, or Scene Switch as they’re also known, is that you can screw a bulb into your table lamp and, using the switch on the lamp, dim the light across three steps.
It works like this:
Step 1: Full power
Step 2: About half power
Step 3: About half of Step 2 power
(The levels differ from bulb to bulb)
In order for the three-step dimmer to work, you need to turn it on/off in quick succession.
Most light sources will remember the most recently used setting.
Three-step bulbs also work for pendants with regular on/off switches attached to the wall.