LEDs (Light Emitting Diodes) are semiconductor devices that emit intense light when electrically charged. They are made up of two materials separated into two areas, the “n” side (anode) and “p” side (cathode). As current is connected to them, the electron rich or deficient particles are balanced and the result is emission of light! Next to the Sun this makes LEDs the most efficient light source ever discovered.
The material of the semiconductor device dictates the dominant wavelength and therefore, the color of the light. LEDs with AlInGaP compound semiconductor can emit in the yellow-red spectrum. And the LEDs using AlInGaN compound semiconductor can emit in the UV-blue-green spectrum. A combination of red, green, and blue LEDs, or a blue or UV LED with phosphors can create white light.
Because LEDs are semiconductor devices, their performances are subject to inherent variability commonly found in semiconductor industry. To improve consistency in performance across the same product, LED manufacturers "sort" LEDs into bins according to different preset parameters, such as forward driving voltage, illumination, etc.