Pretty much every type of lighting technology ever developed has been tried for the purpose of growing plants. This covers conventional incandescent light bulbs, fluorescent tubes, the present market leaders which are high intensity discharge lamps (HIDs) including high pressure sodium (HPS) and metal halide (MH) lamps, and of course most recently LEDs.
Discounting regular incandescent and fluorescent lights, since these are not particularly effective for growing plants indoors, an interesting feature of MH lamps is that they produce light in the blue part of the spectrum while HPS lamps are characteristically yellow (street lighting has used sodium lamps for many years now). Between them they cover both sets of chlorophyll absorption peaks, but obviously you need both types of lamp in order to optimise both the early development and maturation phases of plants. For this reason, some manufacturers have devised combination and switchable versions. It’s worth noting however that although HID lamps are extremely bright (they’re commonly also used as car headlight bulbs) they also get very hot and emit infra red (IR) and particularly in the case of MH lamps ultra violet (UV) radiation. While being potentially harmful in excess (or too close), both IR and UV light can of course significantly benefit many types of plants.
LED grow lamps use four separate LEDs (or LED clusters) each designed to emit light at one of the four chlorophyll absorption peaks. The main advantages of LED technology are not only very precise targeting of the key wavelengths of light, but that they are reasonably inexpensive, very bright, out last every other form of lighting bar none by a considerable margin, draw very little power, give off hardly any heat, and can be switched and programmed to produce whatever levels and mixes of light might be required at any given stage of growth. Don’t forget though that plants, like animals, also need regular down time with the lights switched off – as a rule don’t exceed eighteen hours per day.