Total reflection type two optical lens for LED street lamp

1 technical background

Led solid state semiconductor lighting technology is considered to be the strategic energy-saving technology in twenty-first Century. Many countries and city China, Europe and North America have developed LED road lighting technology and vigorously promote, compared to the metal halogen lamp (MH) and high pressure sodium (HPS), LED lamp has a longer life (more than 5 times); in addition, the LED lamp has better controllability and light effect, can save more than 50%. Another feature of LED street lamp is that the light source does not contain harmful substances. Optical aspects can be realized easily with accurate light and two optical optimization design of small source characteristics of LED chip, the accurate control of the direction of the light, the light of the need to allocate sufficient lighting on the road, to prevent light pollution and glare.

The two optical design is one of the most important techniques to determine the light distribution curve, the output light efficiency, the uniformity and the glare index of the LED street lamp. Most of the high power white light LED in the existing market is the distribution of the distribution of the Lang Bo, the spot is round, the peak light intensity at the location of the full width of the beam angle of about 120 degrees. If there is no LED street after two times the optical design of light shining on the road, so the spot will be a "pie", as shown in Figure 1 (a) shown, about 1 and a half spot will be scattered to the road outside the waste, and in the middle of the spot will be relatively light, to around will gradually dim. This kind of lamp is installed on the road, the street lamp will form a very clear light and dark spot distribution, causing visual fatigue, causing accidents. In this case, the LED street lamp can not be called "energy saving" and "green lighting". The national standard of city road lighting design requirements LED lamp spot Figure 1 (b) shows, spot is rectangular, just enough to cover the road, and has a good uniformity. The two LED optical technique, different from other disciplines, is a cover of non imaging optics and 3 dimensional surface modeling of cross discipline, two optical design can effectively solve the LED lamp light efficiency, uniformity, light distribution angle, glare and security issues, provide compliance with light requirements to the national standard, realize environmental protection and green lighting. In addition, the LED street lamp has better color rendering index (CRI), which can adjust the different color temperature according to the needs, which can meet the different environment of day, night, sunny day and rainy day.

Figure 1 (a) without two LED lamp optical design of the spot, (b) LED street after two times of optical design of the spot Fig. 1 (a) Light pattern without optical design, (b) Light pattern with fine optical design

The total reflection two optical lens can collect all of the light emitted from the LED chip, and re assigned to the designated area, is a good solution for the 180. Free surface light can make the far field angle LED lamp light distribution in bat wing distribution, the light spot is rectangle, and the spot center and edge is relatively uniform, the edge ray principle, the lens can also realize the design of light interception, eliminate glare. The following is a design method of total reflection two optical lens.

Design of 2 total reflection type two optical lens

Figure 2. 3D model of total reflection type two optical lens Fig. 2 Lens 3D modELing

Figure 2 is a full reflection of the two dimensional optical lens of the 3 dimensional model. The lens is composed of 4 parts, a concave cylindrical lens part, a total reflection prism part on the side surface, a total reflection prism part at both ends, and a free surface of the upper surface "W". The lens is used to calculate the luminosity distribution of the light of the type LED, which is 120 degrees along the direction of the X (along the direction of the road), and the direction of the Y in the direction of (perpendicular to the direction of the road). The lens design follow the "edge ray principle" [1], which is in the X direction, the angle between the output light edge light and the optical axis is + 60 degrees, all the other output light distribution within the angle in the Y direction, the output light edge of the angle of the light to + 30 degrees.

The design principle of the lens is shown in figure 3. The Y direction of the light distribution such as the principle, from LED of the middle part of the light is converged by the concave cylindrical mirror, reverse light output all converged to a virtual focus to extend the line "F", "this part of the light F and cylindrical mirror edge is composed of, after the surface after in view of the distribution, plus or minus 30 degrees. The light emitted from the side part of the LED is distributed by the side reflection prism. The incident angle of the incident surface to the outside of the total reflection of light, from the bottom to the top, the reflection angle is gradual, and then after the above output surface refraction, this part of the light is also distributed evenly in the + 30 degrees. Along the X direction of the light distribution principle in Figure 3 right, concave cylindrical lens covering the middle part sent from LED + 76 deg. the surface light, "W" shape of this part of the light distribution in divergence within plus or minus 60 degrees, the light distribution curve and distribution the formation of a bat wing. The lens at both ends of each of a total reflection prism, to play the role of light interception, collect the rest sent from LED + 76 DEG ~90 DEG light (this light without light, direct injection will cause glare), after the refraction total reflection surface reflection lens ends outside and the upper surface of the "W" the surface, re distribution within the beam angle + 30 degrees. In the two part, the light distribution is formed by the superposition of the light beam with a beam angle of + / - 60 degrees.

Figure 3 design principles of Y and X profile Fig. 3 Design on Y and X principles sections