Comprehensive guidance on healthy light environment for children and adolescents (1): What is a healthy light environment?

　　All the energy necessary for life on earth comes directly or indirectly from sunlight. Therefore, in the long evolutionary process, the physiological functions of surface organisms are all affected by light. Almost all plants and animals, including some single-celled organisms, have their own phoreceptive systems, and adapt and adjust accordingly according  changes in light. As an indispensable environmental facr for human survival, reproduction and development, sunlight has a profound impact on mankind.

　　From the time when mankind has mastered the use of fire, artificial light sources have partially replaced the function of sunlight. After a long evolution, from chemical fuels  incandescent lamps, fluorescent lamps, and then  electric light sources such as lasers and LEDs, mankind's pursuit of light has never spped. With the popularity of artificial light sources, a large number of strong light sources such as lighting, display advertisements, and aumobiles are widely used, and the health problems caused by light sources have attracted more and more attention. The wavelength range of light visible  the human eye is 380nm~780nm, and light with different wavelengths causes the color perception of the human eye  be different. Human eyes with normal vision are most sensitive  electromagnetic waves with a wavelength of 555nm under phopic vision, which are in the yellow-green light region of the optical spectrum. What humans see is a colorful world composed of multiple colors,

　　At the same time, this colorful world will have different effects on people's physiology and psychology. For example, seeing red will specifically associate red flowers, flames, etc., and abstractly associate passion, celebration, etc.; harmonious and beautiful colors will make people happy; messy colors will make people mood swings; these are all related  light Neuropsychological response.

　　Excessive or messy light radiation will have adverse effects on the environment and human health, that is, "light pollution". o bright glazed wall tiles, bright white fluorescent lamps, dazzling mirrors, flashing TV or computer screens, even the reflective coated paper of magazines, and excessive outdoor lighting intruding in the room by night advertising lights are all neglected light pollution and serious light pollution. It will adversely affect human normal life and work, entertainment, rest, etc., and even affect vision development, cause cataracts, upset, anxiety, insomnia, and affect hormone secretion.

　　At the same time, light also has non-visual effects. Studies have shown that dynamic light environments with high color temperature and high frequency are more alert  people, and static light with low color temperatures is easier  relax people. A large number of animal experiments have shown that light affects the secretion of various hormones in animals, thereby affecting the biological rhythms of animals, the most significant being the secretion of melanin and gonadal axis hormones; seasonal changes in light will affect the levels of mammalian sex hormones.

　　Light has certain effects on human body temperature, metabolism, hormone production, fluctuations in attention and behavior. Strong light at night can inhibit the secretion of melanin, affect falling asleep, and then affect the circadian rhythm. A number of studies have shown that light has an important effect on the human circadian rhythm and the adjustment of body temperature under different environmental temperatures.

　　As a kind of electromagnetic radiation, when it exceeds a certain radiance or irradiance, it will cause direct harm  human eyes and skin. Phobiological safety is used  evaluate these damages. Different wavelengths can cause harm  human eyes and skin. The damage is shown in Table 1.1.

　　In the light source, the light radiation value of a specific wavelength exceeds the safe range, which will cause the corresponding human body injury. In the world, phobiological safety is usually divided in: no danger, low danger, medium danger, and high danger level. For example, high-intensity blue light can penetrate the cornea and lens of the human eye and reach the macular area, causing great damage  the retina of the human eye, increasing macular pathology, causing eye diseases such as vision loss, cataracts, and even blindness.

　　The phorecepr cells of human vision are the traditionally recognized retinal cone cells and rod cells, and the intrinsic phosensitive retinal ganglion cells newly discovered in this century.

　　Cone cells: Cone cells are also called cone cells in the phosensitive layer of the retina. They are small in number and small in size. There are about 6.5-7 million in a single eye. They are concentrated in the macular area and have the highest density in the central fovea. Cone-shaped cells have low light sensitivity and play a major role when the light environment illuminance value is high. Cone cells have the ability  distinguish spatial details and colors. Cone cells contain three light pigments, which are sensitive  the three colors of blue, green and red.

　　Rod cells: rod cells are also called rod cells (rod) in the phosensitive layer of the retina. There are about 120 million in a single eye, distributed around the retina. The rod cells have high sensitivity in the dark or low-illuminance light environment. Plays a leading role and does not have the ability  distinguish spatial details and colors. Although the ratio of cone cells  rod cells is 20:1, cone cells provide 90% of the information  the brain.

　　Intrinsic phoreceptive retinal ganglion cells (ipRGC): ipRGC is also called non-imaging visual phorecepr cells. It is distributed throughout the retina. There are about 1.5 million in a single eye. It can receive signals transmitted from cones and rods  participate in imaging visual functions. , It is also involved in pupils’ light reflection and emotional control. Light information is transmitted  the suprachiasmatic nucleus (SCN) → hypothalamus → pituitary gland → pineal gland through this cell, inhibits the secretion of melanin, and then regulates the human circadian rhythm. The blue light 435-494nm band is related  human systems and tissues. The role of ipRGC, cells, proteins, genes, etc. are active. This effect and influence is called the non-visual effect of light (or the biological effect of light). The fine structure and function of ipRGC have become a hot spot in current research.

　　Vision is the information input by the human eye  receive external environmental light stimulation, which mainly includes brightness (illuminance), color, shape, movement, and spatial three-dimensional perception. The human visual system has many similarities with the camera system. The human eye is a freely adjustable lens with a diameter of about 24mm, and its structure is much like a camera loaded with film.

　　The tissue structure of the human eye changes with age. Development is a series of processes of cell division, differentiation, morphological construction, and growth. It is a process of interaction and transformation of genes and environmental facrs. The older the age, the gradual aging of visual function, and the weakening of the self-defense function of the retina. In a person's life, the period with the largest pupils is adolescence. The reason is that as age increases, the ciliary muscle of the eye ages, which causes the pupils  shrink and the ability  respond  changes in light decreases. Therefore, children and young people have the strongest ability  respond  changes in light, and they must pay more attention  visual health problems.

　　The refractive system of the human eye has different characteristics at different ages. The whole process changes dynamically from hyperopia  emmetropia and then  myopia, and the process is irreversible. Diopter is under the action of many facrs, or stays in the stage of hyperopia due  poor development, or develops wards myopia due  overdevelopment. In th