As a light source with great development potential, the advantages of LEDs such as long life, solid structure, low power consumption and flexible size have attracted more and more attention. In recent years, LEDs, especially monochrome LEDs are widely used in large screens, signal lights and landscape lighting. With the continuous development of LED technology, white LEDs have continuously made new breakthroughs in parameters such as light efficiency, color rendering, color temperature, power of a single LED and luminous flux of LED modules, and people are full of expectations for LED application in lighting.
However, applying white LEDs to ordinary indoor lighting also faces a series of challenges. For example, 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 energy-saving lamps, the color difference is large, and stability Not enough. Although the research results are gratifying, it still takes some time to produce market-oriented products that truly meet the lighting requirements. This is a fact that LED R & D personnel, manufacturers, and users cannot avoid. Based on the human body ergonomics of lighting, this paper analyzes the current development status of white LEDs and the difference between the normal indicators required by a healthy light environment, and puts forward some suggestions for promoting the application process of LEDs in indoor lighting.
Ergonomics of lighting
Ergonomics is also called ergonomics or ergonomics. It takes the "human-machine-environment" system as the research object, and uses the methods of actual measurement, statistics, and analysis to study the three major elements in the "human-machine-environment" system. Relationship to solve the problems of human performance and health in the system. That is to say, the study of human ergonomics is dedicated to designing and evaluating human needs, human abilities, human limits, and how to coordinate with various tasks, jobs, products, environments and systems. The ergonomics of lighting is to study how the design of the light environment meets human 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 meeting the needs of people's visual functions, so that people can work normally in a suitable visual environment, that is, they can see clearly; and to meet people's psychological needs, that is, they must be comfortable. A recent study showed that light can also affect the body's circadian rhythm and health by affecting the secretion of melatonin in the body. Therefore, a good light environment that considers human ergonomics should be based on human visual, psychological, and physiological needs, and comprehensively consider multiple factors, otherwise it will cause adverse effects on people's work efficiency, mental, or physical health.
Development status of white LED
Light effect
Since the birth of LEDs in the 1960s, LEDs have developed at a rate of "Haitz's law" that increases brightness by 30 times every 10 years and prices by 10 times. According to reports, the current laboratory data of white LED light efficiency has exceeded 100lm / W, and high-power white LEDs entering the commercial field have also reached 40lm / W. With the breakthrough of key technologies, the luminous efficiency of high-power LEDs still has a lot of room for improvement in the future, and it is possible to reach a maximum of 150 to 200lm / W.
Luminous flux
With the introduction of high-power LEDs and breakthroughs in key technologies such as packaging and heat dissipation, the commercialization of 5WLEDs 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 flux of 250lm and 400lm, respectively, have been successfully developed. This makes the process of LED for general lighting a big step forward.
Color temperature and color rendering
The color temperature and color rendering of white LED are closely related to the preparation scheme of white LED. In 1996, Nichia first made white LEDs using the InGaN blue chip plus YAG (yttrium aluminum garnet) $ phosphor powder. Since then, people have used R, G, B three-color chip mixed light and near ultraviolet chip to stimulate R, G, B three-color phosphor mixed light to make white LED.
The method of using blue LED plus YAG phosphor is relatively simple because of its simple process and low technical cost. It is currently the most commonly used method for preparing white LED, but its color rendering index is also relatively low. Adding certain red phosphors and green phosphors can improve the color rendering index, but due to the relatively low conversion rate of red phosphors, it usually causes the attenuation of the overall luminous flux, that is, the decrease in light efficiency. Theoretically, white LEDs with any color temperature and higher color rendering index can be obtained by using near-ultraviolet LEDs and RGB three-color phosphors, but the technology for ultraviolet LED phosphors is not yet mature. The method of coating phosphor with a single chip usually has a color temperature difference of 80 ~ 800K according to the coating technology of phosphor. Multi-chip LEDs can theoretically obtain white LEDs of any color temperature and high color rendering, but due to the different forward voltage and light output of multi-chip LEDs, their temperature characteristics and light maintenance characteristics are also different, so the requirements for circuit design It is relatively high, the technology is not mature yet, and the color temperature difference between modules is large.
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