The most suitable color temperature range of LED lighting fixtures should be the color temperature range close to the natural white light of the sun is the most scientific choice; natural white light with lower irradiation intensity can achieve the incomparable irradiation effect of other non-natural white light; the most economical road surface The brightness range should be within 2cd/m2; improving the overall uniformity of lighting and eliminating glare are the most effective ways to save energy and reduce consumption.
In the era of incandescent lamps and high-pressure sodium lamps, people had no choice about the color temperature of lighting fixtures, so they had to accept and adapt silently. However, entering the era of LED lighting fixtures that can choose the color temperature, what kind of LED lighting fixture color temperature to choose has become a problem that urgently needs to have a clear and clear view on it. This is a major issue related to energy saving and lighting quality, and we cannot afford to deal with it sloppily.
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1. The recognition and response mechanism of the human brain to things
The first reaction of the human brain to obtain images of external things through the eyes is to compare and identify the acquired images with the image information originally stored in the brain memory, and then immediately make corresponding response actions. If the acquired image information is closer to the original stored information, the recognition speed will be faster and the response will be more agile. If the driver is under the low color temperature light that is farther away from the natural light during the day at night, the recognition of the acquired image will be more difficult, the recognition speed will be slower, and the response speed will be slower. The result of a 0.1-second slowdown in response time is enough to cause a sudden spike in the accident rate. In order to compensate for the defects caused by the difference in color temperature between day and night, the only way is to increase the intensity of lighting to improve the recognition speed at low color temperature, which means increasing energy consumption.
During the hundreds of thousands of years of evolution from animals to humans, humans have always lived under the natural light of the sun and carried out all production and social activities. As a result of long natural selection and evolution, the most suitable color temperature range for human eyes is the color temperature range of the natural white light of the sun (5500-7500K). In this color temperature range, human eyes have the strongest ability to distinguish moving and still objects; in this color temperature range, human beings have the most agile response ability to external things. Because most of the object image information stored in people’s brain memory information bank is formed under the irradiation of natural white light. Therefore, the most suitable color temperature range of LED lighting fixtures should be close to the color temperature range of the natural white light of the sun, which is the most scientific choice.
2. The biological and geographical reasons why Europeans like low color temperature
So, why do Europeans like low color temperature? This has its racial and geographical reasons. Europeans are fair-skinned people, and white light will make fair-skinned people look pale. There are even exaggerations to say that it is like the color of the dead, so it is natural for them to prefer warm colors. But we are of the yellow race, and the tint of the natural white light of the sun does not make us pale. In addition, most parts of Europe are located in high latitudes and low temperature areas, which is also the geographical reason for their preference for warm colors. However, we are located in a temperate zone with four distinct seasons, and there is no long cold winter. It is a bit unnecessary to follow the Europeans to choose too warm colors.
The most suitable color temperature range of LED lighting fixtures should be the color temperature range close to the natural white light of the sun is the most scientific choice; natural white light with lower irradiation intensity can achieve the incomparable irradiation effect of other non-natural white light; the most economical road surface The brightness range should be within 2cd/m2; improving the overall uniformity of lighting and eliminating glare are the most effective ways to save energy and reduce consumption.
In the era of incandescent lamps and high-pressure sodium lamps, people had no choice about the color temperature of lighting fixtures, so they had to accept and adapt silently. However, entering the era of LED lighting fixtures that can choose the color temperature, what kind of LED lighting fixture color temperature to choose has become a problem that urgently needs to have a clear and clear view on it. This is a major issue related to energy saving and lighting quality, and we cannot afford to deal with it sloppily.
3. Suitable application occasions for the penetrating ability of yellow light, rain and fog
There is also a saying that yellow light with a low color temperature has a better ability to penetrate rain and fog, so it should be selected. We do not deny the fact that yellow light penetrates rain and fog better than white light. However, we should understand that a large number of street lights work under the condition that sunny days account for most of the time, and rainy and foggy weather accounts for a relatively small proportion after all. Choosing lamps with warm color temperature suitable for rainy and foggy weather, wouldn’t it be overwhelming and putting the cart before the horse? In specific occasions, such as foggy port occasions, it is reasonable to choose low color temperature lighting fixtures. Ordinary road lighting fixtures should choose a color temperature range close to the natural white light of the sun, which is both scientific and energy-saving.
Above, we only explained the reason why the lighting color temperature should be close to natural white light from the recognition and response mechanism of the human brain. Next, we will further analyze this argument from the perspective of color rendering index.
4. Advantages of high color rendering index of natural white light
The natural white light of the sun can be decomposed into red, orange, yellow, green, blue, blue, purple and other continuous spectrums and seven kinds of light with a wavelength of 380nm-760nm after being refracted by a three-sided mirror. Natural white light from the sun contains the complete and continuous visible spectrum.
The reason why the human eye can see objects is because the light emitted or reflected from the object enters our eyes and perceives. The basic mechanism of lighting is to irradiate light onto an object, absorb and reflect it, and then reflect from the outer surface of the object into the human eye, allowing people to perceive the color and appearance of the object. But if the illuminating light is only light of a single color, then all we can see are objects of that color. It goes without saying that if the beam of light is with a complete continuous light
5. Low color rendering index cost of low color temperature
The sun shines on the earth from morning to night, not every moment we feel the sun must be natural white light. Because it is also interfered by the absorption, refraction and reflection of clouds with different thicknesses, the composition and proportion of various spectral lines that constitute natural white light will change. Sunlight in the morning and evening is more severely affected by thick clouds, illumination angles and refraction. Therefore, the color rendering index of the golden sunlight at this time is far away from 100, and it cannot be regarded as natural white light.
According to Kevlin’s definition of color temperature, 2800K-10000K belongs to the color temperature range of sunlight, which is the definition range of color temperature of sunlight in a broad sense. However, only light with a color temperature of 6500K (also known as D65) is set as the standard color temperature of white light, which is also the standard illuminant D65 of CIE. The light with a color temperature of 6500K has the most complete spectrum and is closest to natural white light. The farther a light source deviates from the color temperature of natural white light, the lower its color rendering index will be.
Obviously, the lower the color temperature of the LED, the lower its color rendering index will be than the white LED. Under low color rendering index lights, to see the true original appearance of objects clearly, higher light illumination is needed to make up for the lack of color rendering index. This means that people have to increase the energy input of the light source to obtain the true original appearance of the object displayed under natural white light.
Practice has proved that using a light source close to natural white light requires only a much lower illuminance than other light sources to allow people to truly perceive the true color and original appearance of objects. Low illuminance means low energy input, which means energy saving. So we recommend using a light source close to natural white light as our lighting source.
Due to the technical reasons of LED packaging, LEDs mixed with red and yellow pigments have faster light decay than white LEDs, that is, their luminous intensity must decrease faster than white LEDs. The price to make up for the loss of this light intensity drop is to increase the number of LED lamps assembled, which means an increase in cost and energy, which is also a very helpless result.
6. The cost of light intensity reduction of low color temperature LED
Due to the technical reasons of LED packaging, LEDs mixed with red and yellow pigments have faster light decay than white LEDs, that is, their luminous intensity must decrease faster than white LEDs. The price to make up for the loss of this light intensity drop is to increase the number of LED lamps assembled, which means an increase in cost and energy, which is also a very helpless result.
7. The inevitability of revising lighting standards
The ultimate goal of lighting is to allow people to obtain the clarity of observation of real images of moving and still objects. Nowadays, the emergence of LED lamps with a color rendering index of 70-90 and close to the natural white light of the sun is a good opportunity for us to improve lighting quality and reduce energy consumption.
The color rendering index of high pressure sodium lamps is only 20-30. In the era when it dominated the street lighting system, in order to achieve the recognition and clarity of observing objects under its light, the only way to achieve the goal is to increase the illuminance value. The Ministry of Construction’s “Urban Road Lighting Design Standards” was formulated based on the background of sodium lamps with low color rendering index as the dominant lighting source. These standards were originally beyond reproach. However, this standard is too high when the LED with high color rendering index is used as the lighting source. Because, under the LED light source with high color rendering index, to obtain the clarity of the identification and observation of the real image of the object, it only needs to be far less than the standard of illumination requirements for high-pressure sodium lamps. According to our many years of practical experience, it only needs to be less than 30% of the illuminance intensity of the “Urban Road Lighting Design Standard” issued by the Ministry of Construction to achieve the same or even better identification and clarity lighting effects as high-pressure sodium lamps.
Using the same illuminance standard as high-pressure sodium lamps to regulate LED light sources means unnecessary waste of energy. Excessively high-intensity LED lighting may even lead to complaints that LED lighting is too “dazzling”; reducing the intensity of illumination can not only save energy, but also obtain a “soft” lighting environment.
Therefore, the color temperature range of LED lighting fixtures and the choice of lighting standards are closely related to lighting quality and energy saving. Choosing LED lighting fixtures with a color temperature close to the natural white light of the sun and appropriate lighting standards is a wise, scientific and energy-saving choice.
