Non-imaging optics applied to LED lighting technology characteristics and related design
Non-imaging optics: Different from traditional imaging optics in the past, non-imaging optics focuses not on the quality of the light source that can be imaged and imaged on the target plane.Its main concern is the energy utilization rate of the light source and the specific distribution of the energy in the azimuth angle and space. As shown in Figure 1, in the imaging optical system, it mainly transmits the light intensity and position information of the object point, while in the non-imaging optical system, it mainly transmits and recombines and distributes the object point energy.
Energy collection rate: Non-imaging optics is mainly concerned with energy distribution. If a non-imaging optics model is established, it can be clearly seen that the plane represented by A is the entrance aperture area, and the plane where A is the exit Aperture area. Below we assume that the output aperture area A of the device can let all light exit through this part of the area, and the ratio c between the incident beam area and the outgoing beam area is the energy collection rate. Under normal circumstances, the maximum collection rate of energy in a 2D system is C2D=l/sin, while in a rotationally symmetric 3D system, the maximum collection rate is C3D=1/sin2.
Geometrical optics: At present, geometrical optics has been widely used in the design of optical systems. Both imaging optics and non-imaging optics must be designed based on the theory of geometric optics. There are four basic laws in geometric optics, namely the law of straight propagation of light, the law of independent propagation, the law of refraction and the law of reflection.
Features of LED
As LED adopts the principle of electroluminescence, its characteristics are very obvious, which can be summarized into the following aspects:
(1) Long service life. The service life of general LEDs can reach about 10 years. This is because the LED is different from the traditional light source in the past, it will not suddenly stop working or burn out like a tungsten lamp. Its damage is mainly caused by the gradual decrease of the luminous performance with the continuous passage of time. For example, the LUXEON series products manufactured by Philips, after 50,000 hours of use, their luminous intensity can still be maintained at about 70% of the initial value.
(2) The maintenance cost is lower. Under normal circumstances, the service life of LEDs is equivalent to more than 10 times that of ordinary light sources, which greatly reduces the cost of light source replacement, and correspondingly reduces maintenance costs and labor costs.
(3) Low energy consumption. Compared with fluorescent lamps or incandescent lamps, the luminous efficiency of LEDs is much higher. The XR-E model of LED produced by Gree has a luminous rate of more than 1001m/W. From the perspective of energy saving, the higher the energy conversion efficiency, the lower the power consumption under the same illumination, which is also one of the biggest advantages of LED.
(4) Small size. This feature is mainly for LED chips. At this stage, the minimum size of LED chips can reach the millimeter level. For example, the Rebel developed and manufactured by Lumileds in the United States has a volume of only 3x4.5x2.1 (in mm) after packaging, and a chip size of only 1mmxlmm. Such a small volume is very convenient for optical design, and can effectively reduce the energy loss of the system.
(5) Strong directionality. As far as the distance of light is concerned, LED can definitely be designed as a point light source. Generally, in optical design, in order to simplify the design steps, it is customary to split the required light source into several point light sources, and these light sources can be replaced by LEDs. At the same time, LEDs can also be distributed on the surface of an object, and simulate the shape of the object to emit light, such as landscape lighting, architectural contour lighting, etc.
(6) Solid-state lighting, green and environmentally friendly. LED is a solid-state lighting source, which does not contain easily broken glass material, and has high impact resistance and vibration resistance, so it can be used in relatively harsh environments. At the same time, LED does not contain toxic and harmful substances such as mercury, and is highly environmentally friendly. In addition, the LED does not contain infrared or ultraviolet light, which will not cause damage to the irradiated object, and it also effectively improves the utilization of light energy.
(7) Low working voltage, suitable for working under low temperature conditions. The main working mode of LED is low-voltage DC power supply, which makes its safety fully reflected. At the same time, it can also work under low temperature conditions. Experiments have proved that it can work at -40 degrees Celsius. Based on this point, it can be used in the lighting system in refrigerators and automotive lighting systems.