Dimming - What do the letters R, L, C, CFLi and LED on a dimmer mean?

The letters indicate the electrical profile of the lighting source that the dimmer supports. The electrical profile of a light source determines the way in which the light intensity can be controlled by a dimmer.
'R' refers to resistive, Ohm’s or a linear load, 'C' to a capacitive load, 'L' means an inductive character. ‘CFLi’ refers to economy lamps. ‘LED’ is the abbreviation for Light Emitting Diode or LED lamps. Based on the electric profile, Niko developed various dimming curves, which are perceived naturally by the human eye.