A modern form of light bulb is the LED, or light emitting diode. These use semiconductor technology and are very effective. These also come in many different forms and can be used in many different applications. For example there are LEDs that produce infrared light or ultraviolet light as well as light in the human visual spectrum.
LEDs function just like every other form of semiconducting diode. A current flows in one side and then out the other. However a current cannot flow the reverse direction through an LED. Inside the LED there is a very small hole that is part of he components. When the charge flows through this area it releases photons. These are considered the smallest quantifiable particle of light.
This hole is called a band gap. How big the band gap is is what allows different LEDs to have different wavelengths of light. Many people notice that LEDs that were produced a long time ago are much dimmer than modern LEDs. This is because the components comprising the band gap were made up of a material called gallium arsenide which is very reflective.
LEDs are also extremely efficient. Incandescent light bulbs are notorious for losing the majority of the energy put into them to heat. Some estimates who that they lose 98% of the energy put into them. LEDs produce hardly any heat at all. I have never actually felt a LED flashlight get hot. This also allows them to last much longer. Some sources claim that many of the LEDs produced in the seventies are still glowing today.
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