How does LED work?

LED working principle

As the name suggests, LED is a semiconductor device that can emit light at a specific wavelength (color). Like other semiconductor chips, the LED semiconductor chip (LED's actual light-emitting unit) will also be packaged in plastic or ceramic. Of course, there can be a package can also be a number of chips. When the LED is in the positive conduction (open), the electrons will be combined with the hole, while the release of energy in the form of photons (as shown in Figure 1.1.1). This effect is often referred to as electroluminescence.

Figure 1 when the LED is excited, the electrons and holes are complex, and the energy is released in the form of a specific wavelength (color)

LED technology, in the field of lighting applications there is a commonly used term, known as lighting (SSL:solid state). This is because of the principle of illumination that is different from that of incandescent light (which is achieved by means of thermal radiation in the visible spectrum).

Working principle of white LED

The most common way is to use monochromatic LED (mostly indium gallium arsenide process with blue LED) phosphors with different colors to realize white light, the corresponding LED known as the phosphor LED. high brightness LED (HB LED) excited by blue light through a portion of the fluorescent layer into yellow light, the other part directly to the way through the blue fluorescent layer. Finally, the combination of blue and yellow light.

Figure a: common phosphor based white light LED internal structure

Figure B: blue light produced by the combination of hole and electron

Figure C: part of the blue light directly through the phosphor layer, while the other part of the phosphor layer is converted into yellow light

Figure D: blue and yellow light mixed together to get white light

Based on the spectral analysis of white light LED with phosphor, we can clearly see the blue part of LED and the relatively wide spectral distribution of the yellow light excited by phosphor.

Figure 2

The blue and yellow light can be mixed with white light, and the Newton dispersion experiment confirms this phenomenon.