How LED Works?
LED is the abbreviation of light-emitting diode. LEDs are solid-state lighting components comprised of p-type and n-type semiconductor materials. When a forward voltage is applied to the component, electrons and holes at the vicinity of the p-n junction annihilate each other, dissipating the energy in the form of photons. Depending on the band gap energy associated by the semiconductor materials used to build the LEDs, the wavelength, and thus the color, of the emitted light varies. LED development began with infrared and red devices made with gallium arsenide (GaAs) alloys. With advances in material sciences, new material systems such as gallium phosphide (GaP), gallium nitride (GaN) and indium gallium nitride (InGaN), with various band gap energies are investigated and brought into practical use, enabling the availability of LEDs with shorter wavelengths like yellow, green, blue and purple.
White LEDs for General Illumination
There are two primary ways of making white light using LEDs.
1) One is to place individual LEDs with three primary colors, i.e. blue, green and red, in the same package. The optical mixture of the three primary colors gives white light. The resultant LEDs are frequently called multi-colored white LEDs or RGB LEDs. However, multi-colored white LEDs suffer from color instability and are rarely made for commercial purpose nowadays.
2) An alternative way for making white LEDs involves coating an LED of one color (mostly blue LED made of InGaN) with phosphor of different colors to form white light. The resultant LEDs are called phosphor-based white LEDs. A fraction of the blue light is absorbed by the phosphor, which subsequently emits other colors with longer wavelengths. Depending on the color of the original LED, phosphors of different colors can be employed. Although phosphor-related degradation remains an issue, this type of white LEDs is still the most popular method for making high intensity white LEDs as the design and production of a monochrome light source with phosphor conversion is simpler and cheaper than a complex RGB system.
1) One is to place individual LEDs with three primary colors, i.e. blue, green and red, in the same package. The optical mixture of the three primary colors gives white light. The resultant LEDs are frequently called multi-colored white LEDs or RGB LEDs. However, multi-colored white LEDs suffer from color instability and are rarely made for commercial purpose nowadays.
2) An alternative way for making white LEDs involves coating an LED of one color (mostly blue LED made of InGaN) with phosphor of different colors to form white light. The resultant LEDs are called phosphor-based white LEDs. A fraction of the blue light is absorbed by the phosphor, which subsequently emits other colors with longer wavelengths. Depending on the color of the original LED, phosphors of different colors can be employed. Although phosphor-related degradation remains an issue, this type of white LEDs is still the most popular method for making high intensity white LEDs as the design and production of a monochrome light source with phosphor conversion is simpler and cheaper than a complex RGB system.
