This paper mainly introduces the comparison of key indexes between urban road lighting sources and lamps, compares and analyzes the data obtained from the trial operation of LED light sources and high-pressure sodium lamps, and talks about the development prospect of LED light sources.
Keywords: LED indicators comparative case introduction comparative analysis
At present, China is building a resource-saving and environment-friendly society, and the concept of "green lighting" is gradually gaining popularity. With the continuous progress of science and technology and the rapid development of semiconductor material application technology, low-power LED light sources have been widely used in landscape lighting, and high-power LED street lamps have been paid more and more attention.
High-power LED street lamp is a new lighting method which uses DC low voltage to light LED group to meet the lighting requirements, and has the characteristics of high brightness and good color rendering. In addition, because the input of LED street lamps is low-voltage DC, which can be combined with solar energy, solar LED street lamps become a possibility for future road lighting.
1. Comparison of key indicators of urban road lighting sources and lamps
1. luminous efficiency: Lm/w per watt. That is, the ability of electric light source to convert electric energy into light energy is expressed by dividing the luminous flux by power consumption.
At present, the luminous efficiency of foreign LED light sources is about 75Lm/w in the United States and Japan, and the domestic LED production is about 65 lm/w..
The luminous efficiency of high-pressure sodium lamp light source is about 100Lm/w, and the light flux per w is 25 ~ 35 lm/w higher than that of LED. The luminous efficiency of 400w high-pressure sodium lamp is as high as120lm/w. ..
2. Average life span: in hours. That is, the number of hours when a batch of light sources is damaged to 50%.
The average life of LED light source is more than 50,000 hours, but there are too many complicated factors that affect the life in practical application. In addition to the material, manufacturing process and technology of LED devices, LED particle combination, lamp design, components supporting control circuit, heat dissipation, waterproof and dustproof will all affect the life of LED light source. Therefore, the service life of LED light source > 50,000 hours can only refer to the theoretical service life of the light source.
The average life of high-pressure sodium lamp light source is more than 24,000 hours, and the life of its energy-saving inductive ballast is more than 50,000 hours. After the end of the life of sodium lamp light source, ballast can still be used.
3. Utilization coefficient of lamps: refers to the utilization efficiency of the luminous flux emitted by the light source and the light reflected by the lamp reflector. The Standard for Design of Urban Road Lighting stipulates that the utilization coefficient of lamps is 70%.
LED light source has small beam emission angle and strong directivity, and hundreds or even tens of thousands of LEDs in a lamp can be used to replace high-pressure sodium lamps. This brings the matching problem between LED combined light source and LED lamp. Moreover, the power and volume of each LED are too small, and the output of luminous flux is also small. It is very inefficient to distribute the light directly to the reflector and then use it again (there is no test data, and the opinions are analyzed by visual inspection).
The light source of high-pressure sodium lamp is a linear cylindrical light source, which is radial, and can make good use of the refraction of light through the reflector for secondary distribution of light, so the utilization coefficient is high.
4. Lamps and lanterns must have the light distribution performance of bat wings. Because the distance between the two lamps in the longitudinal direction of the road is about 40m, the two lamps must irradiate the light to more than 20m, form a light intersection between the two lamps, and cover the dark area where the two lamps meet.
LED lamps are limited by the directionality of light sources, which are too small and many, so it is difficult to meet the ideal requirements of bat wing-shaped light distribution. Its maximum light intensity is within 15, and most of the light only shines on the road surface at the lower end of the lamp. Can't cover the dark area between two lamps. See the light distribution curves of the two lamps in Figure 1 and Figure 2 for details.
The light source of high-pressure sodium lamp is not limited by directionality, and a bat wing shape is formed by secondary light distribution, and its maximum light intensity is about 60 ~ 65. It can illuminate farther and cover the dark area between two lamps.
5. Protection grade of lamps: IP. That is, the sealing degree of the dustproof and waterproof lamp. Generally, the requirement for lamps is IP55~IP65, and lamps with two light sources can meet this requirement.
Second, the trial case introduction of LED in road lighting
In order to deeply understand the characteristics of LED street lamps, we made some tentative tests on the secondary roads with little traffic in Changzhou suburbs, and conducted a short-term tracking test. The following briefly introduces the pilot situation:
Lamp parameters provided by the manufacturer:
① luminous flux of the lamp: 8000 lumens; ②LED luminous power:125 w; ③ power consumption:150 w; ④ Power of single LED:1.3w; ⑤ American CREE chip; ⑤ Lamp size: 600*296*2 10.
Experimental test data:
Average illuminance (EAV): 1 8.98L x, horizontal illuminance uniformity (Emin /EAV): 0.07.
Test point 2: Meihua Road, located in Chonglou Development Zone. The width of this motorway is 14m, and 150wLED street lamps are symmetrically arranged on both sides, so the spacing is shortened.
At present, our city chooses different lighting schemes on three roads and tries to install high-power LED street lamps. The situation is as follows:
Test point 1: located at Minjiang Road, Xinbei District, with a width of 9m (see Figure 3 for details). Replace three groups of conventional street lamps, and install three groups of 150wLED street lamps at one side with a distance of 33m and a height of 9m. At the initial stage of installation, after actual measurement, the maximum illumination under the lamp is 66. 1Lux, and the average illumination is 18.98Lux, which can meet the standard value. However, with the extension of the distance, the illumination under the lamp drops rapidly, and obvious dark spots appear between the two lamps (see Figure 4 for details). The lowest illumination value is only 1.4Lux, and the uniformity is only 0.07, which is far from it. (See the measured illumination in Figure 5 for details) is 27m, and the height of lamps is reduced to 8m (see Figure 6 for details). After 55 days of installation, the measured average illuminance is 27.5Lux and the uniformity is 0.09, which is slightly better than Minjiang Road, but its uniformity is still not enough to meet the standard requirements. Through field measurement, the maximum illumination value of 150wLED street lamp can reach about 70Lux at two test points, while the minimum illumination value is only 2. 1Lux. It can be seen that the average illuminance of this high-power LED street lamp can meet the requirements of road lighting under the condition of reducing the lamp spacing, but its uniformity still needs to be improved, and the road zebra crossing is obvious (see Figure 7, Meihua Road Night Scene).
Experimental test data:
Average illuminance (Eav):27.5Lx, maximum illuminance 70. 1Lx, minimum illuminance 2.5Lx, horizontal illuminance uniformity (Emin/EAV): 0.09, power density: 0.79W/m2.
Experiment 3: Street lamps installed by the owner of Electronic Science and Technology Industrial Park in Xinbei District, with a road width of 14m (see Figure 9 for details), with 125wLED street lamps symmetrically arranged on both sides, with a distance of 22m between light sources and 50m between street lamps. For comparison, 250w high-pressure sodium lamps are installed at intervals on the north side (see figure 1 1 for details).
After the lamps were installed for about half a year, the field measurement showed that the average illuminance of led street lamps was only 4.72Lux, and the illuminance uniformity was only 0.04. There is almost no illumination in the middle area of the two groups of LED street lamps, and the minimum illumination is 0.2Lx, but it is found that the maximum illumination under the lamps is 30.7Lux (see figure 10 for details).
Technical parameters of lamps and lanterns:
Power 125W, total luminous flux 8000lm. The rest is unknown.
Experimental test data:
Average illuminance (Eav):4.72Lx, maximum illuminance 30.7Lx, illumination of lighting station 0.2Lx, and horizontal illuminance uniformity (Emin/EAV): 0.04.
Experimental test data:
Average illumination (EAV): 7. 14lx, the highest illumination of high-pressure sodium lamp is 53. 1Lx, the illumination at 30m away from the lamp is 0.8Lx, the highest illumination of LED lamp is 27.4Lx, the illumination at 15m away from the lamp is 0.7Lx, and the horizontal illumination uniformity (Emin/eav) is 0. Comparison between Meihualu LED and high-pressure sodium lamp
Meihua Road Project Case
Light source 150wLED 400w high-pressure sodium lamp
Installation height (m) 8 10
Street lamps are arranged symmetrically on both sides and unilaterally.
Street lamp spacing (m) 27 35
Road width (m) 14 14
Arm length (m) 1 1.5
Elevation 10
Average illumination (lux) 27.5 29.7
Uniformity 0.09 0.35
3. Preliminary analysis of actual use effect. LED street lamp:
First, luminous efficiency:
At present, the average light efficiency of a single LED product reaches 80lm per watt, and the average narrow-band LED illumination is 10Lx (the light efficiency is equivalent to a metal halide lamp). However, the absorption and loss of light by the lamp body and the light that cannot be projected on the road surface should be removed; For different lamp products, the effective light put into the ground needs different system tests.
Second, the pavement uniformity:
From the principle of LED lighting, its directivity determines that the light intensity distribution of LED street lamps is limited, which is essentially different from the way of conventional street lamp light source+reasonable light distribution lamp. Therefore, the maximum illumination value under the lamp is often high, but at the same time its illumination decreases rapidly with the increase of distance, and its illumination area directly affects its uniformity. If the comprehensive index of illumination level is reached, the distance between lamps must be shortened, which will lead to an increase in lamp pole investment and a large number of lamp poles, and will also involve the problem of one-time investment. Therefore, road lighting must have bat-wing light distribution performance. As mentioned earlier, the light distribution curve of LED street lamps (Figure 1) does not meet the requirements of functional road lighting.
Third, power density:
Taking Meihua Road as an example, according to the test data, if the uniformity is good and the distance between street lamps is less than 20m, the power density will reach 1.07W/m2, which is somewhat high. Therefore, in the aspect of LED lighting principle, it is necessary to solve the contradiction between uniformity and power density for LED lamps.
Fourth, life:
The life and power consumption of LED street lamp products should not be limited to the light source itself, but should consider the system life of the whole light source electrical equipment, and all devices in its circuit, such as supporting electrical equipment and cooling system, should be taken into account in order to calculate a more scientific average life.
Verb (abbreviation for verb) radiates heat:
At present, there is no ideal method to solve the heat dissipation problem of LED chips, which leads to a great attenuation of light over time. It has a great influence on the road lighting that is continuously turned on for a long time and all night; As a result, the power of LED street lamps can not be greatly broken, and its light efficiency and stability are also greatly limited. It can be said that this lighting method is not suitable for installation on highways with heavy traffic for the time being.
Six, long-term application needs further testing:
The LED street lamp is still in the experimental stage in Changzhou, and the measured data can't completely judge its optical stability because of the short time, so it needs to be run for some time for further tracking test.
To sum up, with the progress of science and technology, there is great potential to improve the luminous efficiency of light-emitting diodes, which has become a hot spot in the global lighting field. Theoretically speaking, LED with high light efficiency will be a green, energy-saving and environment-friendly new product to replace the traditional light source.
However, in practical application, landscape lighting has been widely used. We think that local lighting, point lighting or auxiliary lighting such as garden lights and lawn lights with low illumination requirements should be feasible; It will take some time to realize large-scale functional road lighting and main lighting in a short time. There are still many problems to be solved to realize the light distribution performance of bat wing and the overall life of LED light source appliances.