Cold LED Lighting Application Analysis
After about 10 years of rapid development, LED lighting has entered a rapid promotion phase, the market application from the initial southern regions gradually to the central and western penetration expansion. But in the actual application we found that the outdoor lighting products used well in the south, to the northern regions, especially in the northeast, Xinjiang and other regions, the application of products subject to new tests. This paper analyzes some key factors affecting LED lighting in the cold environment, to find corresponding solutions to the strategy, and finally give full play to the advantages of LED light source.
The advantages of LED lighting in the cold environment
Relative to the original incandescent, fluorescent lamps and high-intensity discharge lamps, LED devices work much better at low temperatures. This is closely related to the temperature characteristics of LED devices, Figure 1 is a brand of high-power LED devices temperature and relative light output curve. It can be seen that as the junction temperature decreases, the luminous flux of the lamp will increase relatively.
Difficulties and countermeasures for LED lighting in cold environments
Although the LED itself has more advantages in cold conditions, only to clarify these constraints, to find the corresponding solutions, you can give full play to the advantages of LED light source, in the cold environment shine.
1. The low-temperature starting problem of the drive power supply
The main reason is that most of the existing mature power supply solutions, are inseparable from the extensive use of electrolytic capacitors. However, in the low temperature environment below -25℃, the electrolyte activity of electrolytic capacitors decreases significantly and the capacitance capacity decays greatly, resulting in the circuit not working normally. To solve this problem, there are two options.
(1)Use high-quality capacitors with a wider operating temperature range, which of course brings an increase in cost.
(2)Use of electrolytic capacitor-free circuit design, including the use of ceramic laminated capacitors, or even the use of linear drive and other drive solutions.
2. Reliability of plastic materials under high and low temperature impact
According to some domestic and foreign research institutions researchers experimentally confirmed: many ordinary plastic and rubber materials in the -15 ℃ below the low temperature toughness deterioration, brittleness increased. For LED outdoor products, light transmitters, optical lenses, seals and some structural parts are likely to use plastic materials, then the low-temperature mechanical properties of these materials need to be carefully considered.
In addition, LED lamps and lanterns often use plastic parts and metal with the structure. As plastic materials and metal materials in a large temperature difference in the environment, the expansion coefficient difference is large, such as lamps and lanterns commonly used metal aluminum and commonly used plastic materials expansion coefficient difference of about 5 times or more, which may lead to plastic material rupture, or the gap between the two increases, ultimately resulting in the failure of the waterproof sealing structure, and then the product problems.
LED lamps and lanterns in the afternoon near the evening before the light, the temperature may be lower than -20 ℃, and then the night after the power work, due to the heat of the lamps and lanterns, and may make the temperature of the lamp body rose to 30 ℃ ~ 40 ℃ or more, basically every day the lamps and lanterns have to experience A cycle of high and low temperature impact.
At the same time, there is a view that: different visible light through the fog capacity is about the same, the reason is: the size of different photons compared to the size of the relationship between green beans and soybeans, and compared to the size of the fog particles, it is equivalent to a soccer. When the concentration of fog is very large, any light is very difficult to penetrate. This time to show the sodium lamp yellow light than the LED white light fog penetration ability is stronger, the main reason is that in the LED white light irradiation, the fog presents a white blanket, while the yellow light shows a very good induction. The author believes that this view still has some truth to it.
Relatively speaking, the proportion of blue components of high color temperature LEDs is larger, and the proportion of yellow and red light proportion is relatively small. High-pressure sodium lamp and 2700K low color temperature LED, blue component is relatively small, the yellow and red light component is relatively large. And sodium lamp and 2700K LED compared to the LED, there is not much advantage, if you consider the impact of LED color rendering index, then the low color temperature LED has more advantages. Therefore, cold lighting, more consideration should be given to the use of low color temperature LEDs below 3000K, with better fog permeability and induction.
We can see through the analysis of a number of factors in the cold environment, LED as a semiconductor lighting device, has its own many advantages, but there are also some problems that are different from traditional lighting sources, only careful study of these differences, carefully analyze the solution one by one, in order to truly bring out the advantages of LED lighting in cold conditions.
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