Low color temperature, high luminous efficiency LED street light module research (Photos)

1 Introduction

At present, the light source commonly used in road lamps is a high-pressure sodium lamp or a metal halide lamp. The most important feature of these two kinds of light sources is that the size of the arc tube that emits light is small, and the arc tube with a small size generates a large light output and is very high. The light effect, the former includes supporting electrical appliances, up to 110lm / w, the latter including supporting electrical appliances up to 80lm / w. However, when such a light source is applied in a road lamp, only about 40% of the light directly passes through the glass cover to reach the road surface, and the other light is projected through the lamp emitter to project the lamp, and the conventional lamp generally adopting such a light source is basically There are two shortcomings. One is that the illumination in the direction of direct illumination of the lamp is very high, and it can reach 50lx or more on the secondary road. This area belongs to the obvious transitional illumination, and the illumination at the intersection of the two lamps is only under the lamp. The illuminance is 20% to 40%. Second, the efficiency of the reflector of such a lamp is generally only 50% to 60%, so about 60% of the light output is in the lamp, and is projected onto the road surface after losing 40% to 30%. The overall efficiency of such luminaires is generally around 70%. And too much illuminance in the transitional illumination area described above is also wasteful.

Based on the above analysis, the above-mentioned conventional road lamps have a comprehensive effective illumination efficiency (excluding the excessive illumination portion) of only 50%. For the above reasons, the lighting effects (uniformity of road illumination and illumination) of China's secondary trunk roads are currently not up to the CJJ45-2006 and CIE31 and CIE115 standards [1]. As a fourth-generation light source, LED not only has energy-saving and environmental protection effects, but also has attracted widespread attention due to its own characteristics (directionality, high color rendering, easy structure design and convenient control) [2][3][4 ], with the continuous improvement of the luminous efficiency of LED chips, especially the 100lm/w chip, LED road lights will gradually replace traditional road lights (sodium lamps, halogen lamps, etc.). It is not practical to manufacture a single lamp exceeding 80W. The main reason is that it is difficult to dissipate heat and it is difficult to design light distribution. Therefore, the use of multiple LED street lamps with more than 10W lamp modules combined into different powers has become the mainstream of research and market. Since the color temperature of the sodium street lamp is generally lower than 3000K and the color rendering index is lower than 40, the low color temperature light has the advantages of strong ability to penetrate fog and water vapor, soft light, warmth, high reflectivity of the road surface and the like. Therefore, the LED module with low color temperature and high luminous efficiency has become a hot spot in the current market research. This paper focuses on the 12W street light module developed by the company with low color temperature, high luminous efficiency and low light decay.

2. Test and test

The company's researchers have developed a new type of LED street light module for the problems of high attenuation of high-power LED modules on the market and low luminous efficiency of color temperature below 3000K. Its structure is shown in Figure 1. This structure is unique in that the phosphor coating layer is located in the lens, and the phosphor can be injected into the phosphor tank of a specific shape through the small hole, and the shape of the groove varies depending on the shape of the chip array.

1, high refractive lens, 2, chip, 3, gold wire, 4, sealant, 5, bracket, 51, parabolic stent groove, 11, phosphor coating layer, 12, filling phosphor mouth

Figure 1 Schematic and physical map of the company's 12W white LED module

The advantages of this structure: 1. The phosphor and the chip are separated by a sealant and a heat-insulating lens, the temperature of the phosphor can be kept below 40 ° C, and the temperature of the 12 W chip is as high as 80-100 ° C, so the attenuation of the phosphor is small. 2, the shape of the phosphor is easy to design, by designing different phosphor tanks, the phosphor can be excited by the highest efficiency, and the luminous efficiency is greatly improved; 3. The shape and refractive index of the lens are easy to design, and the glass with high refractive index is used. , LED modules with different diffusion angles can be made; 4. The shape of the phosphor makes the point light source emitted by each 1W chip pass through the phosphor layer and becomes a uniform surface light source.

Taiwanese wafer power LED chip, 10 chips, its power is 12W. The prepared 12W LED module was placed in the reliability test equipment, high and low temperature cycle test (-40 ~ 80 °C) for 100 hours, then sampled by Shanghai Semiconductor Lighting Engineering Technology Research Center, using Hangzhou 300 LED light color The integrated measurement system and the LED 620 light intensity distribution tester respectively test the photoelectric parameters and the average light intensity diffusion angle of the sample, and the test method is that the constant current is lit for 5 minutes and then tested. (Our study found that the voltage of the 12-watt LED lamp does not change after 5 minutes of lighting, and the luminous efficiency is basically no longer changed. This method should measure the optical parameters of the LED more accurately). The light decay test was tested after lighting for 5000 hours.

3. Results and discussion

In order to make the data more convincing, the company invited Shanghai Semiconductor Lighting Engineering Technology Research Center to sample and test. Table 1 is the test data of Shanghai Semiconductor Lighting Engineering Technology Research Center:

Table 1 Photoelectric parameters of 12WLED street light module (spectral accuracy: +/-2nm; chromaticity accuracy: +/-0.0015x, +/-0.001y)

Voltage (V) Current (A) Multiplier Operating Temperature (°C) Luminous Flux (lm) Light Efficiency (lm/w) Correlated Color Temperature (k)
12.71 0.9001 22.7 1092.8 95.53 2656

It can be found from the above table that the color temperature of the 12W LED street light module is only 2656K, but its luminous efficiency is as high as 95.53lm/w. Although the luminous efficiency of the high-pressure sodium lamp is as high as 110lm/w, its divergence angle is large and effective. The luminous flux accounts for about 50%, and the LED street light module has directionality, so its luminous flux can be almost fully utilized. In comparison, the application prospect of the LED street light module is better, and the luminous efficiency of the LED chip is continuously improved. Declining, LED road lights will gradually replace high-pressure sodium lamps and other related road lights. The low color temperature and high luminous efficiency lamp module has always been a research difficulty. The low color temperature module developed by the company has a color temperature controllable range of 2000-4000K, and can design color temperature and luminous efficiency according to user requirements.

By continuing to rationally plan the shape of the phosphor coating and the arrangement position of the chip, the total reflection film and the anti-reflection film can greatly increase the luminous efficiency. At present, our laboratory has developed a luminous efficiency of up to 105 lm/w, and the color temperature. It is a street light module of 5W, 12W, 24W, 30W, etc. of 2000-4000K.

By changing the lens and phosphor coating shape, we designed a 12W white LED street light module with different light intensity divergence angles. Now the average light intensity diffusion angle θ (50%) is 65o to illustrate this problem. The illuminance distribution of the 12W LED module prepared in the structure shown in Figure 1 is a regular circle. The 12W white LED is suspended at 1 meter high and its central illumination is 267 lux. By changing the shape of the lens, different illuminance patterns can be designed. At present, the company is designing such products according to customer requirements. as shown in picture 2

Figure 2 Lens and light distribution curve after light distribution design

In practical applications, it is only necessary to install this module on the luminaire to realize rectangular spot illumination. This module is suitable for different types of luminaires, and solves the problem of illuminating the luminaires that cause headaches for luminaire manufacturers.

The Shanghai Semiconductor Lighting Engineering Technology Research Center sampled and tested the light decay of the company's 12W streetlights. The results show that after 5000 hours of lighting, the light decay is less than 1%, which is far lower than other high-power LED modules designed on the market. The main reasons are: 1. The phosphor is away from the heat-generating chip; 2. The phosphor shape is controllable; 3. The stable high-refractive index sealing material and lens.

This module has a wide range of applications, the company used this module to develop a series of floodlights, tunnel lights, street lights and indoor lighting and projector light source, as shown in Figure 3.

Figure 3 Photographs of tunnel lights, interior lights, street lights and downlights based on 12W low color temperature and high luminous efficiency

4 Conclusion

The company has developed a new 12W white LED module suitable for lighting. This module has low color temperature and high luminous efficiency, especially suitable for street lamps, tunnel lights, floodlights and projectors. The technology solves the problem that the current low color temperature and high light efficiency are difficult to prepare. Open up a new way of thinking and method for LED outdoor lighting. The 12W module has been put into the market. At present, the company's R&D personnel have developed 5W, 12W, 24W, 30W series of low color temperature (2000-4000K), high luminous efficiency (laboratory can reach 105lm / w) LED module, this The module's light intensity divergence angle (50%) can be designed to be 30o, 45o, 60o and 70o; the illumination range can be designed as a circle, an ellipse and a rectangle.

references

[1] Urban Road Lighting Design Standards, CJJ45-2006, 2006-12-19 Released, 2007-07-01 Implementation, Ministry of Construction of the People's Republic of China

[2] Steigerwald DA, Bhat JC, Collins D, et al. Illumination with solid state lighting technology [J]. IEEE J. Selected Topics in Quantum Electron., 2002, 8(2): 310-320

[3] Narendran N. Improved performance of white LED [J]. Proc. SPIE, 2005, 5941:1-6

[4] Qian Keyuan, Hu Fei, Wu Huiying, et al. Research on high power white LED packaging technology [J], Semiconductor Optoelectronics, 2005, 26 (2): 118-120

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