LEDs are compact, lightweight, low-drive, full-color, long-life, high-efficiency, vibration-resistant, and easy to control light, providing superior conditions for lighting systems designed for different locations and purposes. People are used to seeing things in the sun. For general lighting, people need mainly light sources close to the quality of sunlight, so white LEDs are an important indicator of semiconductor lighting technology. Since the single LED has low power and low brightness, it is not suitable for use alone. Therefore, it is necessary to assemble a plurality of LEDs together to design a practical LED lighting system. However, there is still a certain distance between the requirements of white LEDs and general lighting, and there are still many technical and cost issues that need to be solved urgently.
1. Overview of main technologies of semiconductor lighting system
1) Thermal management of the lighting system
LEDs are often referred to as cold light sources. This is because the principle of LED illumination is that electrons directly emit photons through recombination without the need for heat. However, due to the existence of Joule heat, LEDs also have heat accompanying illumination, and for high power and multiple LED applications, the heat accumulation is small and cannot be underestimated. LEDs are different from traditional illumination sources such as incandescent lamps and fluorescent lamps. Excessive temperatures can shorten or even terminate their service life. Moreover, LEDs are temperature-sensitive devices. When the temperature rises, their efficiency drops sharply. Therefore, system structure design and heat dissipation technology development are also issues that LED applications need to face. Since forced air cooling is generally undesirable in light sources, heat sinks and other methods of enhancing natural convection cooling play an increasingly important role in LED lamp and light source design as input power increases.
2) Improve color rendering
At present, white LEDs generally use a blue-emitting LED to superimpose a yellow-emitting yttrium aluminum garnet (YAG) phosphor excited by blue light, which is synthesized into white light. Since the luminescence spectrum contains only two spectra of blue and yellow, there is a problem that the color temperature is high and the color rendering index is low, which does not meet the general lighting requirements. The sensitivity of the human eye to chromatic aberration is much higher than the sensitivity to light intensity. For illumination, the color rendering of a light source is often more important than the luminous efficiency. Therefore, adding an appropriate amount of red-emitting phosphor and maintaining high luminous efficiency is an important issue in LED white light illumination.
3) Secondary optical design of the luminaire system
Conventional lamps have long used incandescent lamps and fluorescent lamps as reference materials to determine the optical and shape standards of lamps. Therefore, LED lamp systems should consider the abandonment of traditional lamps and LED light module assembly methods, fully consider their optical characteristics, and specialize for LED light sources. Design different luminaires. The design of the optical system mainly includes the following aspects: 1 According to the requirements of the illumination object and the luminous flux, determine the shape of the optical system, the number of LEDs and the size of the power; 2 design a plurality of LED lighting tubes into a point light source, a ring light source or The "secondary light source" of the surface light source calculates the illumination optical system according to the combined secondary light source; 3 it is important to control the light distribution of each LED tube on the "secondary light source" constituting the illumination optical system design.
Since the beam emitted by the LED is concentrated, it is easier to control, and the reflector is not required to be concentrated, which is advantageous for reducing the depth of the lamp. For example, with a flat mirror optical system, a large surface can be illuminated with only 1 or 2 LEDs, and the depth of the lamp is very thin. With the light guide technology, the LED is directly mounted next to the light pipe, which can greatly reduce the light source and other components. The volume occupied makes an ultra-thin luminaire.