In addition to Tom, Marc and Tony's replies, how about these descriptions:
Lighting from Lamps which do not use Resistance Elements (AKA Fillaments) to DIRECTLY produce Light output, via emissions from the filament only - as with Incandescent Lamps
(Incandescents are mostly a heat / Infrared Light Generator, with White Light being a "Byproduct").
Lighting produced via a Plasma contained within an arc tube, with Light output produced from Photons emitted from inert materials in the arc tube, due to a controlled level of current knocking the Photons loose from the inert materials, while the current flows from one Cathode, through the arc tube, and collects in the other Cathode.
Lighting from Lamps having "Negative Resistance" Characteristics, as opposed to Lamps with a "Linear Resistance" Characteristic - as would be found in Resistance (Filimant) type Lamps - AKA Incandescent Lamps.
Or: (last one)
Lamps which require the Current to be "Ballasted" (automatically regulated) by an external or separate device, in order to operate correctly (and not self destruct instantly); as opposed to Filament Lamps, which do not normally require the Current to be "Ballasted" - due to the Linear Resistance of the Filament.
I have more, but these are boring enough!