Analyzing the application of white light LED in indoor lighting with human ergonomics

As a light source with great development potential, LED 's advantages such as long life, solid structure, low power consumption and flexible size have attracted more and more attention. In recent years, LED, especially monochrome LED, has been widely used in large screens, signal lights and landscape lighting. With the continuous development of LED technology, the light efficiency , color rendering, color temperature of white light LED , the power of single LED and the luminous flux of LED module have made new breakthroughs, and people are full of expectations for the application of LED in lighting.

However, the application of white light LEDs in ordinary indoor lighting also faces a series of challenges, such as the luminous flux of a single LED is still difficult to meet the needs of ordinary lighting, the unit cost is too high, the light efficiency is lower than that of energy-saving lamps, the color difference is large, and the stability is insufficient. Although the research results are promising, it will take some time to produce marketable products that truly meet the lighting requirements. This is a fact that LED researchers, manufacturers and users cannot avoid. Starting from the ergonomics of lighting, this article analyzes the current development status of white light LEDs and the differences between them and the normal indicators required for a healthy light environment, and puts forward some suggestions for promoting the application of LEDs in indoor lighting.

1. Ergonomics of lighting

Ergonomics, also known as human ergonomics or ergonomics, takes the "man-machine-environment" system as the research object, and uses actual measurement, statistics, analysis and other methods to study the relationship between the three major elements in the "man-machine-environment" system to solve the efficiency and health problems of people in the system. In other words, the study of ergonomics is committed to designing and evaluating people's needs, abilities, and limits, as well as how to coordinate with various tasks, work, products, environments and systems. Ergonomics of lighting is to study how the design of the light environment can meet people's needs, so that people can complete various visual tasks faster and better or meet the needs of comfort and health as much as possible.

The lighting environment should fully consider the needs of people's visual functions, so that people can work normally in a suitable visual environment, that is, they can see clearly; it should also meet people's psychological needs, that is, they should see comfortably. A recent study shows that light can also affect the body's physiological rhythm and health by affecting the secretion of melatonin in the human body. Therefore, considering a good light environment for ergonomics should start from people's visual, psychological and physiological needs, and comprehensively consider multiple factors, otherwise it will have an adverse effect on people's work efficiency, psychological or physical health.

2. Development status of white light LED

2.1 Lighting Effect

Since the birth of LED in the 1960s, it has developed at a speed similar to "Haitz's Law" that brightness increases 30 times and price decreases 10 times every 10 years. According to reports, the current laboratory data of white light LED luminous efficiency has exceeded 100lm/W, and high-power white light LEDs entering the commercial field have also reached 40lm/W. With the breakthrough of key technologies, the luminous efficiency of high-power LEDs will still have a lot of room for improvement in the future, and may reach 150-200lm/W.

2.2 Luminous flux

With the emergence of high-power LEDs and breakthroughs in key technologies such as packaging and heat dissipation, the commercialization of 5W LEDs has begun to take shape, which has greatly improved the luminous flux of LED modules. The latest research data from Nichia shows that high-power LED integrated modules with powers of 5.5W and 11W and luminous fluxes of 250lm and 400lm have been successfully developed. This has taken the process of LEDs for general lighting a big step forward.

2.3 Color Temperature and Color Rendering

The color temperature and color rendering of white light LEDs are closely related to the preparation scheme of white light LEDs. In 1996, Nichia first used the method of InGaN blue light chips plus YAG (yttrium aluminum garnet) yellow phosphor to make white light LEDs. Since then, people have used R, G, B three-color chip mixing and near-ultraviolet chips to excite R, G, B three-color phosphor mixing to make white light LEDs. The method of

using blue light LEDs plus YAG phosphors is the most commonly used method for preparing white light LEDs because of its simple process and low technical cost, but its color rendering index is also relatively low. Although adding a certain amount of red light phosphor and green light phosphor can improve the color rendering index, due to the low relative conversion rate of red light phosphor, it usually causes the attenuation of the overall luminous flux, that is, the decline of light efficiency. The use of near-ultraviolet LEDs plus RGB three-primary color phosphors can theoretically obtain white light LEDs with any color temperature and a higher color rendering index, but the technology used for ultraviolet LED phosphors is not yet mature. The method of coating phosphor on a single chip usually has a color temperature difference of 80~800K depending on the coating technology of the phosphor. In theory, multi-chip LEDs can obtain white light LEDs with any color temperature and high color rendering, but due to the different forward voltages and light outputs of multi-chip LEDs, their temperature characteristics and light maintenance characteristics are also different, so the requirements for circuit design are high. At present, the technology is not mature, and the color temperature difference between modules is large.

3. Consider the requirements of ergonomics for white light LED lighting

As mentioned earlier, considering the ergonomics of lighting should consider people's requirements for the lighting environment. The indoor environment is the environment where people spend most of their time living and working, so people's demand for indoor lighting environment is getting higher and higher. Whether these requirements can be met is the key to LED replacing traditional light sources for indoor lighting.

3.1 Visual function requirements

In order to meet people's visual needs, that is, to allow people to see clearly, this requires the lighting environment to have a certain illumination level, illumination uniformity and color rendering.

To meet a certain illumination level, the LED is required to have sufficient luminous flux. Take a small reading room as an example. If the reading room area is 6m×8m, then a luminous flux of about 20,000~30,000lm is needed to meet people's normal reading needs. If other factors are not considered, the application of 200lm high-power particles on the market currently also requires 100~150 particles of LED to achieve such illumination requirements. Since the luminous efficacy of the current better market products is around 30~40lm/W, LED cannot compete with energy-saving lamps or fluorescent lamps regardless of energy consumption or cost. In addition, the immaturity of the optical design technology of LED lamps makes the current light distribution of LED lamps not stable enough, and it also requires a high cost to achieve a certain illumination uniformity. However, for small-area key lighting, using LEDs with a small amount of energy consumption can meet the visual needs, and it is also easier to meet the uniformity. In terms of color rendering, the current white light LED can basically meet the needs of general indoor activities. 3.2 Psychological needs In normal indoor work or activities, people not only require satisfaction of visual functions, but also a certain degree of visual comfort. This is people's psychological need for the lighting environment, which requires that the light environment in the field of view should not have direct glare or indirect glare, the color temperature should be appropriate, and the arrangement of lamps should be comfortable. In terms of the glare requirements of the field of view, white light LEDs are both an advantage and a challenge. Due to the small light point and beam angle of LEDs, the direction of light emission is easy to control, but on the other hand, the light intensity of LEDs is usually more concentrated. If the maximum light intensity distribution is not handled properly, it is easy to cause glare to the observer. Studies have shown that uncomfortable glare not only causes

3.3 Physiological needs

People's physiological needs for indoor lighting are mainly manifested as health needs. In addition to the adverse effects of long-term ultraviolet light exposure on the skin, there are two other ways in which light affects health that are often overlooked. One is that light affects health through vision, and the other is that light affects health through the physiological rhythm system. Two effects closely related to the use of white light LEDs for indoor lighting are the blue light hazard effect on the retina and the light affecting the physiological rhythm system and health of the human body by inhibiting the secretion of melatonin in the human body. Usually, the harm of ultraviolet light occurs in the front part of the human eye, that is, it will cause damage to the cornea. Blue light, because its wavelength is longer than that of ultraviolet light, can reach the retina through the fundus; and its unit energy is the strongest in the visible light range, which is easy to burn the retina and form early cataracts. On the other hand, the secretion of melatonin in the human body is affected by light. When the secretion of melatonin is abnormal, it is easy to cause confusion in the physiological rhythm of the human body, and in severe cases, it can cause cancer or other lesions.

In the area of ​​400~500nm, the energy distribution of this white light LED has an obvious peak. Adding a certain amount of red phosphor can reduce this peak to a certain extent, but the peak of the blue light region of the currently commonly used white light LED has a large overlap with the spectral sensitivity curve of blue light retinal damage and the sensitivity curve of ganglion cells to light that affects the physiological rhythm system, which has to attract our attention. If ultraviolet LEDs are used with three primary color phosphors and RGB multi-chip white light LEDs, these two effects can be ignored.

4. Promote the application of white light LEDs in indoor lighting Although high-power white light LEDs have made great breakthroughs in light efficiency, color rendering and single power, LED manufacturers have also been rapidly updating their achievements. However, considering the ergonomics, LEDs obviously still have a long way to go to create a lighting environment that meets the needs of human habitation. In order to promote more and more reasonable applications of LEDs in indoor lighting, the following aspects are what LED designers , producers and users should pay attention to together. 4.1 Pay attention to reasonable lighting design In terms of visual function needs, the current luminous flux and light efficiency of LEDs are still difficult to meet the needs of large-area general lighting. Therefore, reasonable lighting design is the key to apply LED to indoor lighting. For example, LED can be used for local key lighting, or the easy control feature of LED can be used for auxiliary lighting and dimming design. The design should combine visual function, psychological and physiological needs, take advantage of strengths and avoid weaknesses, and create a healthy and comfortable light environment. 4.2 Pay attention to the close connection between the upstream, midstream and downstream of LED Undoubtedly, the upstream and midstream of LED have played a key role in the development and application of LED technology, but the application and demand of the downstream also play a leading role in the upstream and midstream of LED. Researchers, engineers and designers should strengthen their connections to make the development of the LED industry more reasonable and humane. 4.3 Strengthen LED secondary optical design technology A key technology in the application of LED lighting is LED secondary optical design technology. Through secondary optical design, the light distribution of LED can be optimized, and the light emitted by LED can be made more reasonable while avoiding glare, so as to meet the lighting requirements. 4.4 Formulate LED indoor lighting standards At present, relevant testing departments in China have begun to carry out research on lighting LED testing methods, including the development of testing equipment. The National Technical Committee for Standardization of Lighting Appliances has included the technical standards and test method standards for lighting LEDs in the standard work plan, hoping to promote the development of LED technology and its application in the field of lighting through the formulation of lighting LED standards. For LED indoor lighting standards, the focus should be on the optical characteristics of LEDs, namely, luminous flux, light distribution, brightness, spectral distribution, chromaticity coordinates, color difference, color rendering index, light decay and other indicators. In addition, the characteristics of electrical accessories, mechanical characteristics, temperature characteristics and safety characteristics of appliances should also be taken into consideration. 5. Conclusion The process of applying white light LEDs to indoor lighting has made significant breakthroughs in the past two years. On the basis of considering the ergonomics of lighting, white light LEDs have certain advantages in indoor lighting. However, there are still many shortcomings. LED designers, producers and users should unite to contribute to the development of LED technology, so that the new generation of light sources can play their best role and obtain more benefits as soon as possible.

In this way, the color temperature is generally high. In order to achieve good lighting effects, the color temperature of the selected light source must be adapted to the required illumination. Figure 1 shows the comfort zone corresponding to illumination and color temperature. Therefore, a higher color temperature will also affect the application of white light LEDs in indoor lighting, because it requires a correspondingly high illumination to make people feel comfortable. On the other hand, the flexible size of LEDs gives LED lamps a lot of room for design, which can fully meet the requirements of decoration.