[Hui Cong Lighting Network] Mr. Wu Chunhai from Shenzhen Lighting Environmental Management Center gave a wonderful speech on "Thinking and Choosing LED Street Light Color Temperature" at the 2009 LED Lighting Technology and Development Forum on September 6-7. The following is his main speech. content.
Looking at LED street lights from the perspective of lighting, there are four major problems, such as light efficiency, light distribution, light decay, and color temperature (light color). In recent years, LED street light technology has been changing with each passing day, and optical performance has improved rapidly. From the results of our recently organized LED street light test, 6 of the 27 LED street lights have more than 70Lm/W, up to 81.5Lm/W; the light distribution level is greatly improved, and the uniformity is higher than that of the high-pressure sodium lamp. There are advantages; the light fade problem is significantly improved, which is not inferior to other light sources.
In this context, the color temperature problem began to surface, rising to one of the main contradictions of LED street lights, becoming the focus of recent industry attention. Indeed, the street light is the "dimming master" of the city at night, and its color temperature determines the "ground color" of the night, which is closely related to the daily life of the citizens. Therefore, the color temperature problem of LED street lamps needs to be solved before the scale application, otherwise it may become a huge obstacle to promotion. At present, this situation has appeared in some cities and will be fulfilled in more cities.
By analyzing the physiological and psychological properties of color temperature, Mr. Wu Chunhai explored its relationship with brightness and comfort, and combined with LED street light test, proposed a color temperature range that fits the current state of the art.
Thinking one: Should the study of color temperature of LED street lamps focus on physiological or psychological?
As a new light source, LED street lights are inevitably compared with existing mainstream lighting, especially high-pressure sodium lamps. Color temperature is the main divergence point. LED street light supporters believe that high color temperature white light has intermediate visual effects for road lighting, good visibility, and feels brighter than low color temperature yellow light; supporters of high pressure sodium lamps believe that yellow light is good in fog and feels warmer than White light is more popular with the public. The above statement has its own logic and reason, and it also has certain rationality. However, only the advantages and disadvantages of different color temperatures are listed. It is impossible to find out the main contradictions faced by LED street lamps in terms of color temperature. It does not help to solve the problem, and does not help the promotion and application of LED street lamps.
Therefore, Mr. Wu Chunhai proposed to study the color temperature from the perspective of attributes, namely physiological and psychological. There is no doubt that color temperature has both physical and psychological attributes, and some indicators are even inseparable. For example, the light fogging effect of the light affects the driver's ability to recognize and react, which is physiological; at the same time, the poor ability to transmit fog makes the driver feel embarrassed, and the spirit is highly nervous and psychological. However, from the perspective of research, we need to treat them separately, classify various indicators, methods, contents, etc., and find out the most difficult problems to be solved before the scale of LED street lights.
Physiological research mainly includes indicators such as visibility and recognition ability. It needs scientists to obtain through well-designed experiments. Psychological research mainly includes indicators such as comfort and satisfaction. It is necessary to conduct a situational survey and questionnaire survey for a sufficient number of citizens. Physiological research is based on professional judgment, and its right to speak is in the hands of scientists. Since LED street lights can be used for road lighting, it is an industry consensus, so it will not become an obstacle to scale promotion. The psychological research is different, and the result depends on the subjective feelings of the general public. Since the LED street lamp will change the existing "ground color" of the city night, the acceptance of the public is very important. Therefore, before the scale is promoted, psychological research is more urgent than physiological research.
At present, many cities have rejected the high color temperature LED street lights because of the low acceptance of white light by the public, which has caused the industry to fall into a dilemma in the choice of light efficiency and color temperature of LED street lamps.
Thinking 2: Is LED street light not suitable for road lighting?
Some streetlight units now clearly express their preference for yellow light. Some experts and research institutes claim that Chinese people like the warm white light of 3000-4000K. More LED street light companies think that white light feels good. There are many different opinions.
Here, it is necessary to revisit a case that has been repeatedly mentioned: In 1999, an international brand promoted metal halide lamps in China, and many major roads in Shenzhen, including Shennan Avenue, were replaced with white light metal halide lamps (6000-6500K). . The initial effect was not bad, but the good times did not last long. After 2000, there were complaints from the public. In 2001 and 2002, the complaint reached a peak, reflecting the dim light and feeling bad. Since then, the main road in Shenzhen has gradually changed back to Huang Guang's high-pressure sodium lamp. At the same time, this scene is also staged in other cities. As a witness, I recognize this fact, but I do not agree that the case is interpreted as Shenzhen citizens do not like white light or even Chinese do not like white light. Since there was no complaint from the public at the time of installation, the complaint appeared in one year and was the most in two to three years. According to the road surface measurement data after the complaint appeared, the metal halide light was severely degraded, and the brightness (photographing) was significantly reduced. The asphalt road illumination was only about 10Lx. Therefore, white light is not accepted in road lighting, and may not only be a high color temperature, but a combination of high color temperature and low brightness. According to the explanation in Figure 1, the light is brighter when it is installed, and it is still in the comfort zone, and it will not feel dim. Unfortunately, the metal halide light was badly degraded. After one year, the brightness was noticeably reduced. It fell into the haze area and complaints appeared.
Based on the complexity of psychological experience, there is no scientific investigation and sufficient samples. It is impossible to judge the advantages and disadvantages of white light and yellow light, and it is impossible to conclude that LED street lights are not suitable for road lighting. In the LED streetlight test, we organized 12 road lighting designers from the Shenzhen Municipal Design Institute to go to the on-site questionnaire survey, and the results were yellow, warm white, neutral white, and cool white, each with 3 (see Table 2). . Although the number of samples is limited, it is sufficient to show that different individuals have different preferences for different color temperatures, even for professional groups.
Therefore, it is impossible to presuppose positions in the study of color temperature. Only when combined with the light and environmental conditions, can we get a real answer. From a general perspective, individuals believe that road lighting may repeat the process of indoor lighting, and white light will become the mainstream of the future.
Choice: warm white, neutral white or cool white?
In road lighting, in order to improve people's comfort and satisfaction, high color temperature light sources need to be appropriately increased in brightness compared to low color temperature, but the required amplitude is not large. Taking the LED street lamp test as an example, the average illumination of 27 LED street lamps is only 12Lx, the maximum is no more than 15Lx, and the average color temperature is 5955K. The overall feeling of each lamp is evaluated on the spot (good, good, general, poor). More than the LED street lights account for about 50%. Considering that the test road is a concrete pavement, it is better to increase the estimated illuminance to 15Lx for the asphalt pavement (the above is a preliminary judgment and further research is needed).
At present, 5500-6000K is the mainstream color temperature range of LED street lamps. In contrast, the average light efficiency of the color temperature <5000K is only 45.5Lm/W, and the difference is very obvious.
As we all know, the light efficiency of LED street lights is closely related to color temperature. The light effect of different color temperature of GREE chip is not much different, but the OSRAM chip is not the same. The light effect of different color temperature is quite different. The light efficiency of 6500K chip is 31.8% higher than that of 5700K chip. Therefore, LED street lamps must balance the color temperature and light efficiency, and must fully consider the comfort and satisfaction of the public, and can not sacrifice the light effect for the pursuit of low color temperature. After all, the illuminance and power density values are hard indicators of the Urban Road Lighting Design Standard (CJJ45-2006), which must have higher light efficiency to meet the requirements. At the same time, due to the large price difference between different color temperature chips, cost factors also need to be carefully considered.
In summary, the choice of LED color temperature range needs to fully consider the acceptance of the public and meet the balance between light efficiency, color temperature and cost under the premise of meeting the road lighting design standards. Based on the current technical level of the LED industry, cold white light in the 5000-6500K range may be a better choice.
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