LED lens knowledge

  The lens is made according to the law of refraction of light. A lens is an optical component made of a transparent substance such as glass, crystal, or the like. The lens is a refractor whose refractive surface is two spherical surfaces (part of the spherical surface), or a spherical surface (part of the spherical surface) of a flat transparent body. It has a real image and a virtual image. Lenses can generally be divided into two broad categories: convex lenses and concave lenses. The central part is thicker than the edge part, which is called a convex lens, which has three kinds of convex, convex, convex and concave; the central part is thinner than the edge part, which is called concave lens, flat concave, convex and concave. LED lenses are generally silicone lenses, because silicone is resistant to high temperatures (and can also be reflowed), so it is usually packaged directly on the LED chip. Generally, silicone lenses are small in size and have a diameter of 3-10 mm. And the LED lens is generally closely associated with the LED, which helps to improve the light-emitting efficiency of the LED, and the optical system LED lens that changes the light field distribution of the LED, that is, closely associated with the LED, helps to improve the light-emitting efficiency of the LED, An optical system that changes the light field distribution of an LED. The high-power LED lens/reflector is mainly used for collecting and guiding light of high-power LED cold light source products. The high-power LED lens designs the light distribution curve according to the angle of the different LEDs, and increases the optical reflection to reduce the light loss and improve the light efficiency (and the set aspherical optical lens). The following focuses on the secondary concentrating high power LED lens of PMMA material. a), by material classification 1, silicone lens a, because silicone is high temperature resistance (can also be reflow soldering), so it is usually packaged directly on the LED chip. b. The general silicone lens is small in volume and has a diameter of 3-10 mm. 2, PMMA lens a, optical grade PMMA (polymethyl methacrylate, commonly known as: acrylic). b, plastic materials, advantages: high production efficiency (can be completed by injection molding, extrusion); high transmittance (93% penetration rate at 3mm thickness); disadvantages: temperature can not exceed 80 ° (heat deformation temperature 92 degrees ). 3, PC lens a, optical grade material Polycarbonate (referred to as PC) polycarbonate. b. Plastic materials, advantages: high production efficiency (can be completed by injection molding, extrusion); light transmittance is slightly lower (the penetration rate is about 89% at 3mm thickness); disadvantage: the temperature cannot exceed 110° (heat distortion temperature 135) degree). 4, glass lens optical glass material, advantages: high transmittance (97% penetration rate at 3mm thickness), high temperature resistance; disadvantages: large volume, heavy weight, single shape, fragile, mass production is difficult to achieve, production Low efficiency, high cost, etc. However, the current price of such production equipment is high and it is difficult to popularize in the short term. In addition, the disadvantages of glass compared to PMMA and PC materials are more fragile, and more research and exploration are needed. In the improved process that can be realized now, the non-fragile properties of the glass can only be improved by coating or tempering treatment, although after these treatments The transmittance of the glass lens will be reduced, but it will still be much larger than that of the ordinary optical plastic lens. So the prospect of glass lenses will be even broader. b) Application classification of LED lens 1. Primary lens a. The primary lens is directly packaged (or bonded) on the LED chip holder and integrated with the LED. b, LED chip (chip) theoretically emits 360 degrees, but in fact the chip is placed on the LED bracket to be fixed and packaged, so the maximum illumination angle of the chip is 180 degrees (more than 180 ° range also has a small amount of residual light), another chip There will also be some stray light, so that all the light of the chip can be effectively concentrated by one lens and different light angles such as 180°, 160°, 140°, 120°, 90°, 60°, etc., but different There is a certain difference in the light extraction efficiency of the LED at the exit angle (the general rule is: the greater the angle, the higher the efficiency). c. The primary lens is generally made of PMMA, PC, optical glass, silica gel, etc. 2. Secondary lens a. The secondary lens and the LED are two separate objects, but they are inseparable when applied. b. The function of the secondary lens is to converge the illumination angle of the LED light source again to any desired angle between 5° and 160°. The distribution of the light field can be mainly divided into: circular, elliptical and rectangular. c. The secondary lens material is generally optical grade PMMA or PC; in special cases, glass can be selected. 3) Classification by specification 1. Transmissive (convex lens) a. When the LED light passes through a curved surface of the lens (double convex has a curved surface), the light will refract and condense, and when adjusting the distance between the lens and the LED The angle will also change (the angle is inversely proportional to the distance). The optically designed lens spot will be very uniform, but due to the lens diameter and lens mode, the light utilization of the LED is not high and the edge of the spot has obvious yellow edges. b, generally used in large angle (50 ° or more) concentrating, such as table lamps, bar lights and other indoor lighting; 2, catadioptric (cone or cup) a, lens design in front of the penetration Concentrating light, and the tapered surface can collect and reflect all the side light, and the overlap of the two kinds of light (the same angle) can get the most perfect light utilization and beautiful spot effect; b, also in the cone The surface of the lens can be changed to be mirrored, frosted, beaded, striped, threaded, convex or concave to obtain different spot effects. 3. The lens module a is a multi-head lens which is formed by injection molding a plurality of single lenses by injection molding, and can be designed into a lens module of 3, 1, 5, or even tens of one according to different requirements; Two separate lenses are combined by a bracket. b. This design effectively saves production costs, achieves consistency of product quality, saves space in the lighting mechanism, and makes it easier to achieve "high power" and other characteristics. 4), materials and production 1, LED lens as optical grade products, for light transmission, thermal stability, density, refractive index uniformity, refractive index stability, water absorption, turbidity, maximum long-term working temperature, etc. There are strict requirements. Therefore, the material of the lens must be selected according to the actual situation. In principle, optical grade PMMA is chosen, and optical grade PCs can be selected if there are special requirements. At present, the Japanese Mitsubishi PMMA material is the best (VH001 is a frequently selected brand), and Mitsubishi's branch in China, Nantong Liyang, will be a little less. 2, must be equipped with 10,000 or even higher level of dust-free workshop, operators must wear anti-static clothing, wearing finger cots, wearing masks and other anti-static dust-proof measures, and regular inspection and cleaning of the workshop. 3, must have professional optical injection molding machines such as Toshiba, Demag, Haitian, Zhenxiong and other brands of injection molding machines, and strictly control the injection molding process to get qualified products. 4, product inspection: no bubbles, no depression, no shrinkage, no flow, no crescent; shape accuracy Rt <0. 005 surface roughness Ra <0.0002. 5, the product must be sealed with anti-static dust-proof PVC, and must be completely sealed packaging, storage must be strictly controlled temperature and humidity, and it is best not to store more than one year. From the design and production process of the above LED lens, the seemingly simple LED lens, from design to finished product, has very high requirements on software and hardware, which also causes the price difference of LED lens on the market to be very large. From the bright future of LED lighting, the lens is an essential part of LED lighting, and the market prospects will be better and better. 5), LED lens design and mold processing 1, first depends on the light source (high-power LED), different brands of high-power LED (such as CREE, lumileds, Seoul, Osram, Edison, Changsen source, etc.), its chip Structure and packaging methods, light characteristics, etc. will be different, resulting in the same lens with different specifications of the brand LED will be different; so require targeted development (mainstream brand-oriented), in order to achieve actual needs; Optical design software (such as Tracepro, CodeV, Zemax, etc.) designed and simulated optical running light, designed to obtain the corresponding optical aspheric surface; 3, LED lens itself is a precision optical accessory, so its precision requirements for the mold is extremely high, especially The processing precision of the optical surface of the lens should be 0.1 μm, and the lens eccentricity should be within 3 μm. Generally, the processing of such high-precision molds must have the following equipment: ultra-precision processing machines (for example: PRECITECHNANOFORM350), CNC integrated processing machines, surface grinders, milling machines, CNC electric discharge machines, surface profilometers, etc. 4, the most precise part of the mold is the optical mold, first select the special mold steel, complete the initial embryo, nickel plating and then use ultra-precision processing machine for aspherical surface processing. VI) Advantages 1. No matter how far or near, the lampshade (reflector cup) is not much different from the lens. In terms of uniformity, the lens will be superior to the reflector. 2, with a small angle of the LED lens, the effect is better than the lampshade, because it has to shoot far! The lampshade has been condensed through the lens (because the LED itself must have a lens) and then concentrated by a reticle. This time, a lot of light is wasted. It is better to concentrate on the lens, and the lens's illumination angle is well handled. Another: If the space is ok, using 3 1W is much better than using a 3W. 3. In contrast, the lampshade has a wide range of uniform illumination, but the projection is not good, and the lens is the opposite. 4, LED penetration seems to be higher-end. VII) Light loss considerations 1. The luminous flux of a luminaire with a bulb and a lens actually meets the light distribution required by the standard. It is also necessary to consider factors such as the transmittance of the outer casing, the lens, and the loss of light. The high power of the lamp or the general illumination requires the lens to diffuse the parallel beam to meet the standard requirements. In order to make the optical effect more reasonable, the lamp cover should be divided into rectangular small units in the design. The purpose of this is to break the wave surface of the light wave, so that the product has a uniform appearance. In each small unit, an ellipsoid is used because the surface has curvatures in both the horizontal and vertical directions, so that different diffusion radii can be achieved with different radii of curvature in both directions. Its fundamental purpose is to overcome the deficiencies of traditional technologies and make rational use of luminous flux to achieve uniform and efficient light distribution. In fact, the outer shell of the bulb is PC material (injection finished), and the spherical, pear-shaped and cylindrical bulbs are non-small units and non-planar whole shells, and the light loss is large and the light angle is small. 2. Since one surface of the lens is a curved surface having a radius of curvature in both the horizontal and vertical directions, the incident light can be diffused both in the horizontal direction and in the vertical direction. Since the radii of curvature in the two directions are independent of each other, the two curvatures can be separately adjusted as required, so that the light output is diffused to different extents in both directions. Therefore, using a lens composed of a bidirectional curvature surface, the light output can be more freely distributed according to design requirements, and the luminous flux can be utilized more efficiently, thereby reducing unnecessary waste and glare. Furthermore, since a smooth transition surface is used, the lamp has a uniform transition light distribution and a good appearance. A completely transparent PMMA lighting or lampshade can cause dazzling or glaring chords in the center of the light source, but the brightness is rapidly reduced at the periphery of the light source. Many social occasions and work environment lighting must eliminate this unpleasant atmosphere or minimize the source of eye discomfort. 3. The projection of each lens unit on the body is a rectangle, so that the units can be arranged closely and neatly. The parallel incident beam passes through the refraction of the lens unit to form a uniform diffusion in the horizontal direction and a uniform diffusion in the vertical direction. By adjusting the size of each unit in a group of lenses and the radius of curvature of the two directions, the distribution of the emitted light flux in different solid angle ranges is adjusted to achieve the light distribution required by the design. Since the effect of the incident curved surface is to deflect the light to form a diffusion, the number of cells, the size of the unit, and the radius of curvature of each lens in the product design can be changed according to the actual situation. The actual situation is that the internal grain on the lens of the high-power lens (for dividing the small unit) is made by the manufacturer, and only the lens height, angle, and material are considered when selecting. 4. We choose to place the light source on the inner side of the lens focus. The farther the light source is from the lens, the less the light flux of the light source collected by the lens, so the lower the efficiency of the lens system is. According to the calculation formula of single convex lens: r=(nL-1) f. Where r-convex curvature radius, nL-lens material refractive index, f-lens focal length in the case of selected lens material, the larger the focal length, the larger the radius of curvature. Under the same lens aperture Φ, the larger the radius of curvature, the thinner the lens. The thicker the lens, the more obvious the aberration will be, which will affect the effect. Therefore, choose a lens with a larger focal length as much as possible. At the same time, the focal length increases and the size of the optical system increases. Therefore, the focal length of the lens cannot be pursued to the maximum. Since the lens thickness is not very large, the Fresnel lens is not used, and the cumbersomeness and cost of processing are avoided.