LED stands for light emitting diode, or a diode that is constructed out of materials that emit light when an electrical current is run through them. Sometimes LEDs can be designed to emit ultraviolet radiation, which is dangerous when used in the wrong context but has many useful applications, especially in industrial and medical sectors. In this case, these are known as "curing" lights, for their ability to harden and bond certain substances that are reactive to ultraviolet wavelengths.
Curing Resin
Curing resin is the most common application for LED curing lights. Dentists and industrial processes cure resin most often this way. When dentists use sealants or resins to bond in a fake tooth, fill a cavity or do root work where some type of resin plate is needed, they need to harden the resin in place very quickly. They use a resin that is chemically reactive to ultraviolet light, and then shine the LED light in the patient's mouth for about a minute to cure it. Factories use largely curing lights to cure epoxies and resins on materials such as fiberglass.
Sanitizing
LED curing lights can be used to kill micro-organisms. These LED ultraviolet lights are found mostly in laboratories and other medical facilities where it is very important that specific environments and tools be kept clear of even microscopic contamination. Since LED lights are hand-held, it is easy to quickly sanitize specific objects.
Print Bonding
Factories often use LED curing lights for print bonding, or bonding letters onto materials such as plastic, where ink does not usually stay. They use a special ink that, like the dental resins, is reactive to ultraviolet light and quickly dries and bonds to the surface when exposed to it. The materials are passed under curing lights to quickly adhere the ink. Most keyboards are made this way.

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