Preliminary discussion on LED lighting and its medical effects

introduction

In the early 1990s, a blue LED was invented, and then blue light was used as an excitation beam to illuminate the yellow light phosphor, and part of the blue light was converted into yellow light, and finally white light mixed with blue light and yellow light was obtained. The white LED lamp can be used in the field of general illumination. It is a solid-state illumination source. Compared with traditional incandescent lamps and fluorescent lamps, it has the advantages of high luminous efficiency, long life and dimming. This is a major technological breakthrough and a major revolution in the field of lighting.

Under the vigorous promotion and support of the country, China's LED industry is developing very rapidly, and its application fields are very extensive. The industry has penetrated into the advertising fields such as advertising screens, decorations, landscapes, roads, vehicles, ships, commercial and indoors; and mobile phones, computers, Backlighting of liquid crystal displays such as televisions. There are many domestic LED manufacturers, and the level of production technology is uneven. The quality of products is very different. In practical applications, there are many problems that have not yet been fully recognized by people. Among them, glare and light color are the most prominent. There are many articles in China that discuss blue light problems, etc. 1-3). This article first discusses the working characteristics of LED, and then discusses the medical effects of light color on people, which can cause producers and users to fully understand and make the LED lighting industry develop healthily.

1, LED lighting source

Invented incandescent lamps for more than 130 years, fluorescent lamps have been 78 years old, people have become accustomed to living, learning and working in this kind of light color lighting environment. At present, the illumination color environment of LED lamps has not been fully accepted by people. For this reason, the light color characteristics should be as close as possible to the two types of lamps.

In order to understand and understand the working performance and characteristics of LED light source, we will briefly introduce the working performance of energy-saving fluorescent lamps, which is beneficial to compare each other and deepen the understanding of LED light source.

1-1 characteristics of energy-saving fluorescent lamps

Energy-saving fluorescent lamps use 254nm and a small amount of 185nm ultraviolet rays generated by mercury atoms in the excitation ionization discharge to illuminate the three primary colors of red, green and blue phosphors, and obtain illumination colors of different color temperatures of 2700-6500K. Fluorescent lamps are surface-emitting, uniform in brightness, radiating around the walls of glass tubes. The color temperature difference is small, the working condition is stable, and the product consistency is good. The luminous efficiency is up to about 110 Lm/W, generally 60-80 Lm/W; usually the high color temperature lamp has low luminous efficiency, and the low color temperature lamp has high luminous efficiency.

The high-quality energy-saving fluorescent lamp products have a working life of more than 10,000 hours; most fluorescent lamps are only about six or seven thousand hours. Due to the gas discharge characteristics of the fluorescent lamp, continuous dimming is not possible, and the dimming amplitude is very limited; the time from start-up to normal operation is long, and the response speed is slow. In addition, the working substance mercury in fluorescent lamps is a harmful substance, which causes environmental pollution.

1-2 LED light source working characteristics

LED light source is a device that emits light when it passes through a solid-state semiconductor. It has LED modules, components, lamps, etc., collectively referred to as COB (Chip on Board). Only LED lamps are discussed here.

Nowadays, the popular LED illumination source is a chip that uses gallium nitride (GaN) to emit blue light with a wavelength of 450 nm and then excite the phosphor. The white light LED lamp synthesized by blue light and yellow light has high color temperature, high luminous efficiency and poor color rendering, but its output light still contains nearly 50% of blue light. In order to obtain a medium and low color temperature LED lamp, the blue light beam is irradiated onto the red and green rare earth phosphor powder, and the medium and low color temperature radiation light can also be obtained. If the ratio of the phosphors of the respective colors is adjusted, a lamp having a high color rendering index Ra = 80-90 is obtained. However, the luminous efficiency is lowered, and the LED lamp is significantly smaller than the high color temperature. Obviously, the LED light source has high color temperature and high luminous efficiency; the color temperature is low and the light effect is low, which is opposite to the characteristics of the fluorescent lamp.

The LED light source has a small light-emitting area, is point-emitting, has a high surface brightness, and has a directional radiation with a small solid angle. The light emitted by the LED radiation is compared with the original fluorescent light source and the like, and contains a lot of blue light, and the LED lighting can make people feel uncomfortable. Moreover, blue light has many effects on humans, such as biochemical effects, physiological and physical effects, and psychological effects. It is now called the so-called "blue light effect."

1-3 LED lighting source application

The outstanding advantages of LED light source are high luminous efficiency and long life. At present, the highest luminous efficiency is as high as 190Lm/W or more (about 140Lm/W in China); theoretically, the working life is about 30,000-50,000 hours. Affected by the driving power supply, the actual service life is 1-2 million hours. At present, under the situation of energy saving, environmental protection and protection of the environment, the energy-saving characteristics of LED light sources are very attractive. If you use LED electric bulbs to illuminate, instead of using ordinary incandescent bulbs, the energy-saving effect is very big. Domestically, there are LED bulbs, downlights, PAR lamps, spotlights, etc. instead of incandescent lamps. Compared with energy-saving fluorescent lamps, the improvement of light efficiency is not very large. Compared with fluorescent tubes, straight-tube LED lamps can double the luminous efficiency. However, LED lamps can be continuously dimmed, which is also conducive to energy saving. .

The operating characteristics of the LED light source are highly discrete and the stability is poor. When the operating current or ambient temperature changes, its luminous efficiency and color temperature will change. During the working life, the light effect will gradually decrease, and the light color will drift. Secondly, the temperature resistance of semiconductor nodes is poor, and most LED light sources are provided with heat dissipating components. Once the temperature of the node is too high, the working stability of the lamp becomes poor, even fails, and the life is shortened. It is quite obvious that LED light sources must never be used in higher temperature environments.

Compared with energy-saving fluorescent lamps, LED light sources sold in large quantities in the market have relatively poor light color quality. In the light environment of many LED lighting, people often feel the summer like the blink of an eye. At present, there are not many high-quality LED products in the domestic market, and some low-priced and inferior products are everywhere, which will definitely endanger human health.

2. Visual light environment

Light can bring useful information to humans in terms of vision. About 80% of the information in the human body is obtained by vision. Vision determines the human feeling. It first focuses on color and is also a precious function of visual features. There are also some differences in the perception of color, depending on what state the eye is in.

In the process of evolution, human beings undergo various environmental changes, and their genetics will also change, adapting in the gradual evolution. However, this change is a very slow and gradual process, and it may take several generations to adapt to changes in the light environment. The current color environment of LED light sources varies greatly, making it difficult to adapt.

For more than a decade, white LED light sources have been widely used in the information industry, indoor and outdoor lighting, transportation and other fields. The light environment around people is undergoing a period of great change, the changes are extremely rapid, the environmental light pollution is serious, and people's vision is difficult to adapt, and they will feel uncomfortable. In this case, it is necessary to dig deeper into the cause and take effective measures to develop a reliable LED light source. If the technology is not mature or inferior LED lighting products, we should try our best to monitor and not enter the lighting market, otherwise it will seriously endanger human health.

3, the light transmission of the eye

In the surrounding natural sputum, there are ultraviolet light, visible light, and infrared light. Among them, human vision can be perceived as visible light, and the light transmission of the eyeball is related to the wavelength of light.

3-1 ultraviolet light

Far ultraviolet UV-C (<280nm) can be absorbed by the cornea; UV-B (280-315nm) and UV-A (315-380nm) are absorbed by the cornea and crystal, UV-A has a small amount of reachable Fundus choroid.

If under intense ultraviolet light, the epithelial cells of the corneal surface will undergo a photochemical reaction, causing corneal cracking and epithelial keratitis. Ophthalmitis can occur in ophthalmitis such as arc welding, snowy eye on snowy mountains, or under ultraviolet germicidal lamps. Under weaker ultraviolet light, mainly water crystals are damaged, resulting in cataracts.

3-2 visible light

Visible light (380-780nm) is accepted by the eye, and then passed through the cornea, aqueous humor, crystal water, nitrate body, etc., and finally imaged on the retina. The imaging process is the same as that of the camera, which forms a visual organ with the optic nerve and central nervous system. After receiving the light signal, the eye transmits it to the nervous system. It has strong adaptability to the environment and can correct the data of the central nervous system. For LED illumination, the most important thing is blue light, with a wavelength range of 380-550 nm and a peak of light wavelength of 450 nm; its wavelength is short, and it is easy to pass through the eyeball and reach the retina compared with other visible light. If the temperature is high, a coagulation effect will occur, which may result in a cataract. In modern daily life, there are blue children's toys, laser pointers, etc. If used improperly, it will damage the retina, choroid, depigmentation spots, and seriously damage the visual function.

3-3 infrared light

Infrared has near-infrared IRA (780-1400nm) with poor water absorption, and has excellent permeability, which can reach the fundus. Mid-infrared IRB (1400-3000 nm) and far-infrared IRC (>3000 nm) can be absorbed by the water in the cornea, aqueous humor, hydrocrystals, and nitrate bodies. For example, glass processing artisans, researchers of infrared lasers, etc., often have cataract eye diseases.

4, glare

The glare is mainly determined by the brightness of the illuminant. If the luminous flux of the illuminant is the same, the smaller the illuminating area, the higher the surface brightness. The LED light source has a small light-emitting area and a high brightness, which causes a so-called "glare". Secondly, the higher the color temperature of the light source, the richer the blue light, the stronger the ability to penetrate into the eye and the greater the irritability. If the eye is directly looking at the bare light source, it is very obvious that it feels uncomfortable, distracted, or decreased in visual ability, which can damage the retina.

How to reduce glare is what LED light and luminaire design manufacturers should try to do. In the LED backlight template of the liquid crystal display, a light scattering plate is disposed to increase the light-emitting area, and the light of each light-emitting point can be mixed with each other to obtain a planar light source with uniform brightness and color temperature. In the same way, in front of the light output of the LED illumination source, a scattering bulb or shell wall is arranged; or a diffusing cover plate is placed at the exit of the lighting fixture to increase the light-emitting area and obtain a relatively uniform radiation, thereby reducing Glare pollution.

5. Blue light effect and photobiosafety (medical effect in light environment)

LED lighting source is a new industry, and the technology is still in the development stage. If the human body is exposed to LED light for a long time, optical radiation safety may occur. At present, research on various effects of human body is very active, such as photochemical and biological effects such as retinal damage, arousal disorder, sleep disorder, life rhythm disorder, and psychological effects that affect mood, spirit, emotion, appetite, fatigue, and calmness. In order to prevent the occurrence of safety hazards, the IEC International Standards Agency and the domestic national standards body have formulated and promulgated the "Photobiosafety of Lamps and Lamp Systems".

Only the blue light effect is discussed here, and it has some useful results; and the most prominent difference between the LED light source and the original illumination source is that the blue light is rich, and the impact on the human body is most obvious.

5-1 Photochemical action and macular degeneration

The location imaged at the center of the retina is called the fovea, which is the macular area. The central fossa is slightly concave, and there is a macular pigment (or yellow pigment) in the surrounding diameter of about 200um; it is a place where a large number of cone cells are concentrated, and a large number of nerve cells are concentrated, so that the object can be clearly seen. Elephant. The rod cells are mainly distributed around the center fossa, and the number is about 10% of the cone cells.

Blue light causes photochemical reactions that damage the retina. It acts on the retinal cells of the retinal pigment and retinal pigment of the visual cells, producing important oxides. The fat mass of the rod-shaped, conical layer cell membrane is also oxidized, causing damage to the visual cells; moreover, it will damage the epithelial layer of the retinal nerve.

With the increase of years, the new abnormal blood vessels of the reticular formation produced under the retina, or the slow shrinkage of the visual cells, can cause macular degeneration. Macular degeneration has a complex relationship with genetic and environmental factors. However, the oxidation of light is an important basic element. From incandescent lamps, fluorescent lamps, to the current LED lighting; it is conceivable that human beings are in the blue light that causes light barriers, and the current exposure is greatly increased. Secondly, the current low level of people, the opportunity to view the LCD screen has increased a lot, and the duration is long. The visual function will be gradually damaged, and the myopia of adolescents will increase. When entering the old age (>50 years old), the incidence of blinding macular degeneration will increase. Due to decreased vision, abnormal color vision, dyslexia, and the color of objects are not visible, and the quality of life is significantly impaired. It is said that the incidence of the disease is related to ethnicity, with the highest whites, the lowest blacks, and the yellows. In order to reduce the absorption of short-wavelength light such as glare and blue light, specific filter glasses are also used for protection.

5-2 Physiological effects

Different colored light environments can affect the physical and psychological emotions of human beings. In recent years, due to the appearance of blue light in LED lamps, fear of its negative effects, the use of color light (such as color fluorescent lamps), white light, monochromatic light (single wavelength) illumination, physiological measurements of humans. To understand the effects on the autonomic nervous system and the central nervous system, from body temperature, blood pressure, heart rate, skin conductance GSR, brain wave a wave attenuation coefficient AAC and so on.

5-2-1 sedation and awakening

In the shade, it is illuminated by a blue fluorescent lamp (wide wave domain), which has a calming effect and can be used to prevent suicide and prevent crime. Light blue light is good for patients to reduce fever or lower blood pressure; let trauma patients restrain impulses and irritability. The red light makes people feel bright and eye-catching, excited and energetic.

Kobayashi7) used three types of white light, the color temperature was 3150K, 5200K, 6800K under the lighting test, the 6800K daylight color lighting environment, the expansion of blood pressure (ie low pressure) is higher than the neutral and warm white lighting environment, indicating the former It has a clear arousal effect on the heart.

It is well known that high color temperature white light contains more blue light, which can effectively enhance the activity of brain function and invigorate the spirit. If the factory production workshop uses higher color temperature lighting, it can improve production efficiency and have a clear visual environment. The backlight of the LCD screen is a high color temperature LED light source for a clear view. In the low color temperature lighting environment, it contains more red light, which makes people warm and comfortable, quiet and relaxed, and has an increased appetite. In the home life lighting, you should choose a medium and low color temperature light source of less than 4000K, which is good for rest and sleep.

In the case of red, green, and blue monochromatic light, the arousal effect on the heart has a similar result to that of white light, that is, the blue light-induced arousal effect is the strongest.

Compared with the characteristics of white light/monochromatic light, the above-mentioned blue light-containing color light has the opposite effect, and why it causes its cause, and further research is needed.

5-3 circadian clock and melatonin

After the eye receives the light, there is a third kind of light-receiving cells, called retinal ganglion cells. After the light reaches the retina, it passes through the hypothalamic pathway to the upper oblique cross nucleus (SCN), and is connected to the pineal gland by its own specific neural pathway, which is the center of the brain's biological clock. The pineal gland will secrete melatonin, and its changes will immediately dissolve into the flowing blood, regulating the effects of thermoregulation, sleep awakening, and autonomic nervous system. The circadian rhythm feels the light receiving cells, and its sensitivity is closely related to the light energy and color of the illuminant, that is, the light color and light intensity are related to the inhibition of melatonin secretion.

Morita8) reported the red, green and blue colors, and detected the metabolites of melamine in human urine under the illumination of 1000Lx, respectively, to understand the impact. It shows that the inhibition rate of melatonin is small, the green light is the largest, and the blue light is slightly lower, that is, the blue-green light inhibition rate is large. With 6500K and 3000K white light, under the same illumination, the former's daylight color has twice the inhibition rate of melatonin than warm white.

As can be seen from the above discussion, a high color temperature fluorescent lamp or an LED lamp contains a large amount of blue and green light in white light. It has a high awakening effect and creates a serious and quiet atmosphere. However, for those who work late at night or stay up late, if the illuminance is high and the time is long in the high color temperature environment, the secretion of melatonin will be severely inhibited, especially within about 3 hours after midnight. The peak period. If you can't live according to the laws of the biological clock for a long time, you will develop sleep disorders and even seriously harm your body.

For people with seasonal affective disorder (SAD), most of them are in autumn and winter, especially in the north, with short sunshine hours, long sleep time, increased appetite, weight gain, and prone to depressive symptoms. High-power light source with high color temperature rich in blue-green light can be used for glare treatment, which will inhibit the secretion of melatonin and boost the spirit.

In the light receiving system of the biological clock, the light radiation contains a large amount of light having a short wavelength, and the influence is large. Among them, the blue light of the wide band has a calming effect; while the white light with short wave light or the blue light of narrow wave has obvious awakening effect. Light is closely related to the autonomic nervous system and the central nervous system; on the contrary, it has an important influence on the biological clock.

6, the conclusion

LED is an energy-efficient, long-life light source with a third-generation illumination source with dimmable and intelligent control. Recently, due to the sharp drop in market prices, the country is rapidly spreading into various sectors and sectors. However, the light environment safety caused by LED light sources has not been recognized and fully understood by relevant management departments, enterprises and users.

In terms of the glare and blue light effects produced by the LED light source, there is not much chance of causing an acute disorder; however, after a period of time, the visual function is deteriorated. It is a very slow accumulation process, and when it comes to the old order, it finds the symptoms of visual blindness. All in all, the light that makes people feel uncomfortable can cause eye damage. Of course, the impact or damage to people's psychology should also be considered, but the mechanism is complex, and the reliable conclusions of the research are not many, and it needs further study in the future.

At present, we must first pay attention to the application of the object and occasion, children and children try to use low color temperature LED lighting, the eyeball crystal is pure, the high color temperature lamp is easy to penetrate the blue light, causing damage to the retina. Young and middle-aged people should use high-grade color temperature as the propaganda, but the elderly prefer high-temperature temperature illumination. Because of the turbidity of the eyeball crystals, the visual acuity is poor, showing varying degrees of cataract, which hinders blue light penetration. The above shows that blue light is less harmful to the elderly, and younger and middle-aged people are larger; it is very harmful to children and young people, and it is best to choose a high color rendering light source with color temperature ≤ 3500K 9).

The indoor lighting in the living room should use medium and low color temperature LED lights. While many people in China are accustomed to high color temperature lighting, they must use high quality products with high color rendering. High color temperature lamps can be used for tall buildings, halls, outdoor roads or plazas, but glare must be controlled to achieve uniform illumination distribution. In particular, all kinds of liquid crystal displays have blue light overflow, which also inhibits the secretion of melatonin and damages the retina.

In order to reduce the harm of LED lights, we are also looking forward to the improvement of lighting technology, materials and processes. How to make the outer bulb or the inner wall of the shell have uniform scattering of the beam to reduce glare; at the same time, limit the output of the blue light, it is best to try to convert the blue light twice and use it effectively.

I would like to thank Liu Jun, the attending physician of the Department of Ophthalmology, Zhongda Hospital affiliated to Southeast University, for his support of this work.

This article gives a brief introduction to our understanding. The Department of Biological Science and Medical Engineering of Southeast University is carrying out in-depth research on related topics. Big data analysis technology will bring more scientific evidence to improve the quality and development of domestic LED lighting products. , common business. There must be something wrong with this article, please correct me.

references:

(1) Chen Chaozhong Shi Xiaohong Liu Lei White Light LED photo-biological characteristics China Lighting Electric 嚣 2013 (4)

(2) Zhang Yuemin Joe updated the safety of photobio in blue light in LED lighting. China Lighting Co., Ltd. 2013 (6)

(3) Hu Jinghui Fu Xiaoqi talks about LED lighting blue light hazard and rich blue light environment China Lighting Electric Power 2013 (11)

(4) Zhu Yuhua's "Energy Saving Fluorescent Lamp Technology" (Training Handout)

(5) Tail Flower Mingguang Eye Disorders Lighting Society (Japanese) 2013 (9)

(6) Takahashi Rika Blue Light Physiological Surface and Function Lighting Society (Japanese) 2013 (9)

(7) Kobayashi H, et Physiological Respones to Illuminace and Color Temperature of Light, The Annals of physiological anthropology 1992 (11-1) pp. 45-49

(8) Morita T, et Inhibitory Effect of Light of Different Wavelengths on the Fall of Core Temperature dueing the Nighttime, Japanese Journa of Physiology,

1995 (45-4), pp. 667-671

(9) Zhu Yuhua Pan Youbin Yan Zhenzhi. The influence of lighting color on children's vision and emotions. Proceedings of China Long Triangle Lighting Technology Forum. 2005

Editor: Yingzi

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