Thinking and Choice of Color Temperature of LED Street Lights

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, the relationship between brightness and illumination and comfort is discussed. Combined with the LED street lamp test, the color temperature range corresponding to the current technical level is proposed.

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, the author proposes 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.