The problems in the application of LED street lamp (two)

Under the situation of global energy crisis and environmental pressure, the application of LED light source in road lighting has become a hot topic in recent years. LED device products applied to the street, what are the special requirements of the technology, and the traditional LED lamp high pressure sodium lamp compared with what advantage, what is insufficient, how to solve a series of problems that are worthy of our study.

Optical design and heat dissipation are the main technical problems of LED street lamp

Although the speed of high power LED lamp development soon, but in the application still exists to varying degrees, two lumens of low watt lighting effects of low level, low light efficiency, fast decay, short service life, color temperature deviation, color, not a driver fault and a series of problems. Two optical design, thermal design and power supply voltage regulator system design and other major technical issues, is to improve the luminous efficiency and extend the life of the key.

In order to give full play to the advantages of semiconductor light source, the two optical system design of LED is very important for the distribution of light and optical output efficiency of LED lamps. Good road lighting requires LED street lamp with a rectangular light type, all the light emitted by the street can just cover the road, and the light pollution outside the road is almost zero. Dr. Jiang Jinbo of Hong Kong Polytech University introduced the design of two kinds of LED lamps:

The first kind of LED street lamp is made up of an axisymmetric full reflection lens or a reflecting cup, and the LED lens module is arranged on an arc surface to generate a rectangular light distribution. The introduction of total reflection lens can greatly improve the efficiency of light utilization, but the arrangement of the curved LED module makes the design and mechanical structure of high power LED more troublesome.

The second kind of LED street lamp adopts the unsymmetrical freeform lens, which can be used to complete the rectangular light distribution directly from a single LED optical element. The LED module only has a rectangular lamp with a light simple arranged in a flat plate can be the LED street in the mechanical structure, the cooling and power supply control is relatively simple, different grades and different road light pole height road lighting only need to increase the number of LED modules can be different. The adoption of the two optical element of the asymmetric free-form surface can make the rectangular light distribution of the LED street lamp directly on a single LED module.

The whole street lamp only needs to arrange the LED module array in the same direction, so as to simplify the design of the street lamp mechanism, heat dissipation and control power supply. Should be developed for the packaging of light source light source, more reasonable and full use of light emitted by the light source, so that the whole lamp light efficiency. At present, there are three types of radiation in LED, such as Lambertian, lateral jet, bat wing, rectangle, butterfly wing, and spotlight. Through the two optical design, the illumination range and the luminosity curve of LED meet the requirements of road lighting.

LED is embedded in the use of lighting equipment, because of the large amount of heat of the LED chip, the key technology in the production of high-power lamps is "heat". Although the luminous efficiency is getting higher and higher, but the heat of the LED chip is still very large. PN junction temperature increased by 10 degrees, the life of semiconductor devices to reduce the number of times of 1. The high temperature of the LED chip leads to the deterioration of the chip itself and the performance of the encapsulation resin, which eventually leads to the decrease of the luminous efficiency and the shortening of the lifetime.

At present, various production units have taken different measures of heat dissipation, mostly for the overall, systematic design concept of heat dissipation, the use of high-performance thermal conductivity materials. Such as aluminum die-casting mold, aluminum extrusion heat sink, integral dentate toothed fin, extruded aluminum profile bar tooth length fin radiator, thermal conductivity and external tooth structure piece, natural convection heat dissipation body. There are super alloy heat pipe (100 times the thermal conductivity of pure copper) and high density aluminum fins. The heat generated by the chip is rapidly transferred from the point source to the line source, so that the heat is evenly distributed to the radiating fin. The heat sink down, to avoid the dust accumulation of guano. Chip packaging, lighting and other factors may cause light dissipation.

Price is still the biggest obstacle to large-scale application of LED street lamp

At present, the cost of LED street lamp is still far from the high-pressure sodium lamp, a LED street lamp price of 4000 yuan --8000 yuan, or even higher, and a set of imported brands of high pressure sodium lamp (including lamps, complete sets of electrical light source) price of not more than 1500 yuan. As far as the current situation is concerned, LED street lamp is too expensive, the price is as high as 3-5 times. So even if the power consumption of LED street lamp is only 1/3 of the high-pressure sodium lamp, but because the price is much higher than the high pressure sodium lamp, LED street lamp instead of high pressure sodium lamp cost recovery cycle will be very long.

Therefore, LED street lighting in the road to promote the official market, the price and cost is still the biggest obstacle. To make the LED street light to compete with the existing lighting prices, the cost of the manufacturers need to decline. The near future can only be in the LED technology continues to mature, luminous efficiency continues to improve the premise, through the LED's life advantages, energy-saving advantages to make up for the disadvantages of the lamp price.