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.