I. working principle of LED
As the name suggests, a light-emitting diode (LED) is a semiconductor device that emits light at a specific wavelength (color).
Like other semiconductor chips, LED semiconductor chips (the actual light-emitting units of leds) are also encapsulated in plastic or ceramics.
Of course, a package can have one or more chips.
When the LED is in the positive pilot (open), the electrons recombine with the holes and release energy in the form of photons (as shown in figure 1.1.1).
This effect is often called field luminescence.
Figure 1 when the LED is excited, electrons and holes combine, and energy is released in the form of photons of a specific wavelength (color)
LED technology, in the lighting application field has a commonly used term, called solid state lighting (SSL: solid state lighting).
This is because, unlike the illumination principle of incandescent lamp (luminescence is achieved by radiating heat in the visible part of the spectrum), the technology referred to in solid state lighting is achieved by solid-state field luminescence.
How white leds work
The most common method is to use monochrome LED (mostly blue LED with indium gallium arsenic process) and different color phosphor to achieve white light. The corresponding LED is called as fluorescent powder white light LED.
Eventually, the combination of blue and yellow light makes up white light.
Figure a: the common internal structure of fluorescent powder-based high-light white leds
Figure b: blue light photons produced by the combination of holes and electrons
Figure c: part of the blue light passes directly through the phosphor layer, while the other part is converted into yellow light when passing the phosphor layer
Figure d: the blue and yellow parts are mixed together to get white light
In the spectrum analysis of white LED based on phosphor, we can clearly see the blue part directly excited by LED and the yellow part stimulated by phosphor.
Figure 2 white light can be obtained by mixing blue light and yellow light, which is confirmed by Newton dispersion experiment.