Recently, I heard many experts and scholars that the LED as a street lamp to replace the high-pressure sodium lamp is still not mature in technology. The main reasons are as follows:
1. LED luminous efficiency cannot be compared with high pressure sodium lamps
2. LED illumination is too concentrated, and the uniformity of illumination is poor
3. The long-term light decay of LED street lamps is serious and the life is not long.
4. Unstable LED luminescence (short-term light decay), which changes with time and season
5. LED street lights themselves are too heavy, which is not conducive to installation and wind.
6. LED street lamps are too expensive to be popularized.
Of course, all of this is based on the experience of many domestic test circuits. There is a certain basis.
However, the performance of the domestic test circuit can not represent the current status of the LED is worth exploring.
1. Luminous efficiency problem
At present, the luminous efficiency of LEDs is not as good as that of high-pressure sodium lamps. LEDs currently operate at 65-75 lumens per watt, while high pressure sodium lamps can reach 125 lumens per watt. However, the spectrum of high-pressure sodium lamps is more concentrated in yellow, and its color temperature is only 2000-2500 o K, while the color temperature of LEDs is higher, which can reach 3500-4500 or more. In addition, the light of the high-pressure sodium lamp is emitted everywhere, and a large part of the light cannot reach the road surface. Also, the color rendering index of the high-pressure sodium lamp is only 20 to 40, which is dim; and the color rendering index of the LED is high, which can reach 75-80. So the road is bright and comfortable. Therefore, from the actual luminous effect, the LED can be much higher than the high-pressure sodium lamp. The 100W LED can replace the 250W high pressure sodium lamp or the 300W mercury lamp. The 100W LED has an output luminous flux of only about 6250 lumens (after secondary optics design, there will be a loss), the lumens when reaching the road surface is still 6000 lumens, and the average illumination of the road surface can reach 16Lux (12m high pole). The output luminous flux of a 250W high pressure sodium lamp is 20,000 lumens. But the number of lumens reaching the road is only 7000 lumens. The illuminance of the road surface is about 30-40 Lux. Due to the difference in color rendering coefficient, the illumination correction factor of the LED is 2.35 times, and the correction coefficient of the high pressure sodium lamp is 0.94 times. Therefore, after the 100W LED is corrected, the illumination of the ground is 37.6Lux, and the corrected illumination of the high pressure sodium lamp is 28.2-37.6. The two are equivalent. Therefore, 100W LED can replace 250W high-pressure sodium lamp, LED can save 2.5 times.
2. Irradiation uniformity problem
Indeed, if the secondary optical design is not carried out, the illumination of the LED is relatively concentrated, so the secondary optical path must be designed to make the light intensity bat-shaped. So this problem is very easy to solve.
3. LED light fade problem
Some merchants now use hundreds of φ5 low-power LEDs in order to reduce costs. However, the light decay of this low-power LED is very serious, according to its light decay to 80% of the life of only 1000 hours. Therefore, as a street lamp that requires long-term use, it is absolutely impossible to use such a low-power LED. As a high-power LED, its light decay is much better. However, many domestic manufacturers can only achieve a 10% drop in 10,000 hours.
Far from meeting the requirements for use.
In fact, LED life issues are mainly caused by long-term work at high temperatures. The life at different junction temperatures is shown in the following figure:
When the junction temperature is raised from 115 ° C to 135 ° C, the lifetime is reduced from 50,000 hours to 20,000 hours.
At present, the luminous efficiency of LEDs has not been raised to a very high degree, and it is only possible to improve the heat dissipation to extend the life of LEDs.