Application Analysis of LED Lighting in Cold Area
After 10 years of rapid development, LED lighting has entered a rapid promotion stage, and the market application has gradually expanded from the initial southern region to the central and western regions. However, in actual application, we found that the outdoor lighting products used in the south are well tested in the northern regions, especially the northeast and Xinjiang. This article analyzes some of the key factors that affect LED lighting in cold environments, finds out corresponding solutions, and finally brings out the advantages of LED light sources.
I. Advantages of LED Lighting in Cold Environment
Compared to the original incandescent lamp, fluorescent lamp and high-intensity gas discharge lamp, the operating performance of LED device is much better at low temperature, and it can even be said that the optical performance is better than normal temperature. This is closely related to the temperature characteristics of the LED device. Figure 1 is a graph of the temperature and relative light output of a high-power LED device of a certain brand. It can be seen that as the junction temperature decreases, the luminous flux of the lamp will increase relatively. According to the heat dissipation law of the lamp, the junction temperature is closely related to the ambient temperature. The lower the ambient temperature, the lower the junction temperature is bound to be. In addition, according to Figure 2, we can see that lowering the junction temperature can also reduce the light decay process of the LED light source and delay the service life of the lamp, which is also a characteristic of most electronic components.
Difficulties and Countermeasures of LED Lighting in Cold Environment
Although LED itself has more advantages in cold conditions, it cannot be ignored that in addition to light sources, LED lamps are also closely related to driving power, lamp body materials, and foggy weather, strong ultraviolet and other comprehensive weather in cold environments. Factors have brought new challenges and troubles to the application of this new light source. Only by clarifying these constraints and finding corresponding solutions, can we give full play to the advantages of LED light sources and shine in the cold environment.
1. Low temperature startup problem of driving power supply
人 Everyone who develops power supplies knows that low temperature starting of power supplies is a difficult problem. The main reason is that most of the existing mature power solutions are inseparable from the extensive application of electrolytic capacitors (see Figure 3). However, in a low temperature environment below -25 ° C, the electrolytic activity of the electrolytic capacitor is significantly reduced, and the capacitance capacity is greatly attenuated [1] (see Figure 4), resulting in the circuit not working properly. To solve this problem, there are currently two solutions: one is to use high-quality capacitors with a wider operating temperature range, which of course will increase costs. The second is the circuit design using electrolytic capacitors, including ceramic laminated capacitors, and even other driving schemes such as linear drive.
In addition, in low temperature environments, the withstand voltage performance of ordinary electronic devices such as MOS tubes will also be reduced, which will adversely affect the overall reliability of the circuit, which requires special attention.
2. Reliability of plastic materials under high and low temperature impact
According to experiments conducted by researchers at some research institutes at home and abroad, many ordinary plastics and rubber materials have poor toughness and increased brittleness at low temperatures below -15 ° C [2, 3] (see Figure 5 below). For LED outdoor products, transparent materials, optical lenses, seals and some structural parts may use plastic materials, so the low-temperature mechanical properties of these materials need to be carefully considered, especially the load-bearing components, to avoid lamps in Under the low temperature environment, it will rupture after being hit by strong wind and accidental collision.
3. LED light color problem
After entering the autumn and winter season, the foggy weather in the north will gradually increase. Of course, heavy fog is not a special product of the alpine region, it is everywhere in the world, but in these alpine regions, in addition to the problem of the penetration of fog, there is also the problem of feeling comfort and environmental harmony.
Regarding the problem of the fog penetration of LED lights, the industry has been discussing a lot, so is there any difference in the penetration of fog of light of different wavelengths, and how much is the difference between the yellow light of sodium lamps and the white light of LEDs? How about it?
Viewpoint 1: At a certain fog concentration, light with different wavelengths has different fog penetration capabilities due to different diffraction capabilities. This view has also been confirmed by some related research experiments at home and abroad: Among monochromatic light, the yellow light has the strongest fog penetration ability, followed by red light, green light and blue light [4].
From the analysis of multiple factors in the cold environment, we can see that LED as a semiconductor lighting device has many advantages of its own, but there are some problems that are different from traditional lighting sources. Only careful study of these differences In order to truly show the advantages of LED lighting in cold conditions, one by one, carefully analyze and solve them one by one.