A simple dimmer, or one of these 3 step dimmers work by reducing the voltage going into the lamp.... so 230v full brightness.... 115v half bright etc.
Halogens and old filament bulbs work perfectly well at lower voltages... just dimmer... um obviously.
Fluorescent lights and LED lamps only work at full voltage because of the electronics involved. Although some work between a range of voltages, the brightness is the same.
Dimmable LED lamps require special dimmers designed for the purpose, and it’s a little hit and miss getting them to work.
Good quality dimmers and good quality lamps are required