With the continuous improvement of full-color LED display technology, outdoor full-color LED display has gradually replaced traditional outdoor media and become the mainstream outdoor information display media. Along with the outdoor full-color LED display, in addition to colorful multimedia advertisements and beautiful colors, there is also light pollution caused by outdoor LED display screens, which has an impact on people's vision health and safe travel. To this end, some domestic cities have recently introduced a series of regulations to control light pollution, and at the same time removed a large number of LED displays that cause serious light pollution. Then, how to reduce the light pollution of the LED display from the source has become an urgent problem to be solved in the healthy development of the outdoor full-color LED display industry. There are different ways to prevent and control outdoor light pollution. There is no uniform definition of light pollution. It is more acceptable to say that light pollution is a bad lighting environment caused by the adverse effects of spillover and stray light. At present, regarding the light pollution of outdoor lighting, there is no internationally accepted definition and restriction standard in various countries. The International Commission on Illumination (CIE) has conducted visual studies on the light pollution of outdoor lighting and proposed corresponding limits for different types of light pollution. Regarding the prevention and control of light pollution of LED displays, in addition to the limit value of the maximum brightness of LED displays issued by Shanghai, there is no light pollution restriction standard for outdoor LED displays. There is no uniform definition of understanding light pollution. It is more acceptable to say that light pollution is a poor lighting environment caused by the adverse effects of spillover and stray light. In a narrow sense, it is the negative influence of harmful light, the quantity or direction of which is enough to cause people to be irritated, uncomfortable, inattentive or to reduce the perception of important information such as traffic signals. Excessive light and stray light that also have adverse effects on animals and plants are harmful light. From this definition, two points can be seen: First, light pollution is for things in the nighttime light environment; second, light pollution is not defined by the amount of light determined, but whether the emitted light is negative to the environment. Influence, so light pollution cannot be evaluated solely on the basis of the brightness level or amount of light emitted by an area or a lighting device. The International Commission on Illumination (CIE) on the impact of outdoor lighting on residents, mainly using four technical parameters for evaluation, including light intrusion, building exterior and signboard luminosity, glare and night sky glow. Light intrusion refers to the light that enters the house through the window. Building exteriors and signage luminosity are illuminant-based parameters used to assess the luminosity from the exterior walls and signage of buildings. The glare generated by residents refers to the irritability, distraction or discomfort caused by residents looking directly at bright lighting equipment. The glare generated by the road user is used to measure the disability glare caused by the road user looking directly at the bright light source from the normal viewing direction, feeling irritated, distracted or discomfort. Night sky glow means that the night sky is illuminated by artificial lighting and natural atmosphere and celestial factors. Light from outdoor lighting, including direct upward spillage and light reflected from the ground, can cause night sky glow. The glow of the night sky increases the brightness of the dark part of the sky, weakening the contrast between stars or other celestial bodies and the background of the night sky, thus affecting the ability of astronomers to observe celestial bodies. The purpose of preventing light pollution is to reduce the amount of harmful light to a level that does not harm the surrounding environment and people, while meeting the lighting requirements. The guiding idea is to reduce or eliminate the part of the light that produces light pollution. The International Commission on Illumination (CIE) recommends that different areas be divided into four types of lighting areas, such as intrinsically dark, low-illuminated areas, medium-illuminated areas, and high-illuminated areas, based on general ambient brightness. There are different ways to control light pollution in different areas. The first is the prevention and control of light intrusion in residential areas. The prevention and control of light pollution in residential areas is mainly to reduce the light intrusion of residential windows. The International Commission on Illumination (CIE) imposes strict restrictions on light intrusion in residential homes. The second is to affect the prevention and control of pedestrian glare. The light pollution that poses a hazard to pedestrians mainly comes from the brightness of the light surface of the luminaire itself and the brightness of the light reflected from the road surface or other surfaces. The International Commission on Illumination (CIE) and some developed countries have adopted a method that stipulates the maximum luminous intensity or brightness of the luminaire. The third is the prevention and control of the upward beam of light that produces night sky glow. The light source of the outdoor luminaire emits light in different directions, and the light in the effective range that needs to be illuminated is useful, but there is also spilled light in the range where illumination is not required, resulting in light pollution. In particular, the overhead light will produce night sky glow, which will form a serious night sky light pollution. Internationally, different countries and professional associations have strict control over the shooting. The International Commission on Illumination (CIE) and the United Kingdom have limited the proportion of the total luminous flux of the lamps. Outdoor full-color LED screen light pollution prevention is a new field In order to solve the problem of light pollution on the display screen, the best solution is to reduce the amount of light emitted by the display screen through technical means, thereby reducing the problem of light pollution of the upper light. The research on light pollution of outdoor full-color LED display is still a relatively new field. At present, there is no unified standard that can be accepted by the industry. Referring to the research results of light pollution of outdoor lamps by the International Commission on Illumination (CIE), the light pollution of LED displays is also It involves light intrusion, brightness of LED display, glare and night sky glow. Global and professional associations lack uniform regulations on the light pollution of LED displays. Combined with the regulations of the International Commission on Illumination (CIE) for various outdoor light sources, this paper will conduct a preliminary discussion on the light pollution of LED displays. First, the light intrusion prevention and control in residential areas. The LED display does not define the light intrusion in the residential area. Because in addition to the LED display, there are other light sources such as outdoor street lights. For the light intrusion restrictions in residential areas, the relevant restrictions of the International Commission on Illumination (CIE) can be referred to, but the specific values ​​of light pollution of LED displays cannot be separately distinguished. To reduce the light intrusion of the LED display to the residential area, the light intrusion of the LED display can be reduced by adjusting the brightness of the LED display and reducing the amount of light emitted. The second is to affect the glare of pedestrians and the prevention of display brightness. The interference of LED display glare on pedestrians involves personal evaluation of the brightness of the display screen, which is difficult to define. The International Commission on Illumination (CIE) conducted a visual test of glare sources and limited the brightness of glare sources. In addition, on June 17, 2013, the Shanghai Municipal Bureau of Quality and Technical Supervision released the nation's first LED display brightness limit standard DB31/708-2013, the maximum visible brightness limit and measurement of public area light-emitting diode (LED) display. Method, the maximum brightness value of the LED display is limited. The third is the prevention and control of the upward beam of light that produces night sky glow. Because the LED display is symmetrical, the upper light in the upper viewing angle becomes a source of light pollution in the residential area and the night sky glow. Due to the symmetrical illumination characteristics of LED displays, it is not possible to limit the maximum proportion of total luminous flux that can be achieved by the International Commission on Illumination (CIE). So far, there are no relevant restrictions on the light pollution problem of LEDs on LED displays. In order to solve the problem of light pollution on the display screen, the best solution is to reduce the amount of light emitted by the display screen through technical means, thereby reducing the problem of light pollution of the upper light. In order to reduce the light pollution of the display screen, the industry has proposed many solutions for light pollution of LED display screens. There are four main measures: First, reasonable planning of display area and installation position. According to the distance of viewing, the surrounding environment and the viewing angle, the display area and location are reasonably planned. The second is the choice and design of the playback content. Try not to use a white background as the playback screen. Try to use a softer background. The screen should have a transition when changing. Don't use too many pictures. The third is to use multi-level grayscale correction technology to improve color softness. The LED display uses more gray levels and looks softer in color and transitions naturally. The fourth is to use an adjustment system that automatically adjusts the brightness. Different time and ambient brightness vary greatly. If the brightness of the display is greater than the environment, especially at night, strong glare will cause people's eyes to adapt. With the automatic brightness adjustment system, the broadcast brightness suitable for the environment can be automatically converted to avoid light pollution. LED Display Reduces Light Pollution The device-level solution can reduce light pollution by shifting the energy of the upper viewing angle to the visible range of the lower viewing angle by asymmetrically designing the LAMP device. In addition to the above-mentioned commonly used measures to control light pollution, there is a device-level solution that reduces light pollution by reducing the brightness of the light in the upper and lower visible areas. To reduce the light pollution of the LED display, the best way is to control the direction of light emission and the distribution of light energy. That is, in the effective visible range, all are useful light, and it is necessary to concentrate the light energy as much as possible within the effective visible range. Light in the invisible visible range is harmful light, and it is necessary to minimize the distribution of light energy in the invisible visible range, thereby achieving the goal of reducing light pollution. The asymmetric optical design of the LAMP device reduces light pollution. The display screen is usually installed at a certain height and is installed perpendicular to the horizontal plane. People usually look up at the display screen, the lower viewing angle is the effective viewing range, and the upper viewing angle is the invalid visual range, which causes serious light pollution. In order to achieve energy saving and reduce light pollution, according to the application environment and viewing habits that LED displays usually look up, the idea of ​​optical asymmetry of LAMP devices is proposed. By asymmetrically designing the LAMP device, part of the energy of the upper viewing angle is transferred to the visible range of the lower viewing angle, thereby increasing the brightness in the effective viewing range of the lower viewing angle, and reducing the light pollution in the invisible visible range of the upper viewing angle. the goal of. Reduces light pollution in the invisible visible range of the upper viewing angle. In order to compare the light pollution of the asymmetric LAMP device and the normal LAMP device in the invisible visible range of the upper viewing angle, the power of the asymmetric LAMP device case and the normal LAMP device case are adjusted to be the same, and the brightness under different viewing angles in the upper viewing angle range is comparing. In the upper viewing angle range, from the comparison of the brightness of the asymmetric LAMP box and the brightness of the normal LAMP box, the LAMP device with asymmetric optical design can reduce the light pollution by 10~50 under different viewing angles. Light pollution within the visible range. The brightness in the effective viewing range of the lower viewing angle is the effective brightness, and the higher the brightness of the asymmetric LAMP than the normal LAMP, the better. The brightness in the invisible visible range of the lower viewing angle is harmful brightness, and the brightness of the asymmetric LAMP is as small as possible, which can reduce light pollution in the ineffective visible range. When the horizontal 0 viewing angle brightness value is the same, in the lower viewing angle invalid viewing range, when the horizontal viewing angle is greater than 60, the brightness falling speed of the asymmetric AB series LAMP device box is much higher than the falling speed of the normal LAMP device box, so The brightness of the asymmetric LAMP cabinet is lower than that of the normal LAMP cabinet, that is, the optical contamination of the asymmetric LAMP device is lower than that of the normal LAMP device in the invisible range of the lower viewing angle. The upper and lower viewing angles of the related links are perpendicular to the normal plane of the LED display screen, and the LED display screen is divided into upper and lower parts, which are called an upper viewing angle and a lower viewing angle. The lower viewing angle of the LED display is perpendicular to the visible range below the normal plane of the display. This is the effective display range of the LED display, and the viewer usually looks up. The upper viewing angle of the LED display is perpendicular to the visible range above the normal plane of the display. This is the invalid display range of the LED display, and the viewer usually looks down. Effective visual range and invalid visual range The effective visual range of the LED display refers to a spatial range consisting of a vertical viewing angle and a horizontal viewing angle by the viewer under a reasonable viewing distance and a reasonable viewing angle. The effective viewing range is a description of the spatial extent that the viewer can look up at the display screen and can be composed of a vertical viewing angle and a horizontal viewing angle. The vertical effective visible range angle is in the range of 5 to 45 with the horizontal normal plane, and the horizontal effective visible range is 60 degrees from the vertical normal plane, and a total of 120 is a range of viewing angles, and the space formed in this range becomes effective. Scope of view. Other ranges than the effective visible range become invalid visual range.
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