Two Ways to Make Light
How about a quick refresher on how these different lights work ? The incandescent is the simplest light you can make. Basically it's a tungsten wire in a glass container. When you run an electrical current through the wire, it gets hot enough to glow. If the wire were exposed to air, it would burn and break—that's why it’s sealed in a bulb. But that's it. The problem is, because it makes light based on its temperature, most of the energy it uses is lost as heat.
Now for the LED, or light-emitting diode. (I often say "LED light," which I admit is redundant.) These create light with a solid-state device. A semiconductor material contains an electron energy gap. When a current passes through this gap, it produces a particular wavelength—hence, a particular color—of light. That’s an oversimplification, but it’s fine for now.
But how do you make white light? There are two options. First, you could have three LEDs—a red, a green, and a blue. Combine these and you get white light (more on this below). Second, you could make an ultraviolet LED with a fluorescent coating. The UV light excites the electrons in the coating to produce many different colors of light. This is how old-fashioned fluorescent tubes work, except that the UV light is produced by LEDs instead of an excited gas.
To see how much better an LED is than a plain old incandescent, here are two pictures. The top one, taken with a normal camera, shows how much visible light each one emits—pretty similar. The bottom one is a thermal image taken with an infrared camera.