I'm setting up a light dimmer an have found a adjustable part for setting the "phase angle of light bulbs". That is a literal translation from German. You can see the adjuster in the picture.
My perspective of how the dimmer works is that it just zeroes some parts of the sine shaped voltage therefore reducing the power that reaches the bulb.
What is the purpose of that switch, both functionally (what it does) and conceptually (why and how it's done)?