Light security analysis of LED display screen
1. Optical safety classification
In general, optical security can be divided into the following two categories, namely, photobiosafety and interference with light.
This type of light safety is mainly studied in the fields of ultraviolet, infrared, blue and visible light radiation damage to human tissues. The common photobiological hazards mainly include the harm of photochemical ultraviolet to human skin and eyes, the harm of blue light to human retina, the harm of infrared dressing to eyes and the harm of light and heat to skin.
All sensory organs in the body, the eyes are the most important part of a, its ability to repair itself is relatively weak, once the external optical radiation will cause irreversible damage to the eyes, even if the visible light are likely to hurt people's eyes, such as shorter wavelength blue light can cause retinal photoreceptor cell damage, serious when can cause pigment epithelial function degradation, and like a high strength of irradiation can lead to thermal damage of retina.
Interfere with the light
Interference light can be divided into two kinds: directness and indirectness. The latter refers to the problem caused by the reflection of light onto the surface of an object that does not appear directly in the field of vision.
Through the investigation of some LED display manufacturers in China, it is found that the maximum brightness of LED display is 6 000~8 000 CD /m2, which does not reach the minimum brightness of photobiosafety problem. Therefore, LED display does not cause photobiological harm including blue light harm to human retina. In view of this, the following strong color focus on LED display interference light problem analysis.
2. Causes of LED display interference light
Their own reasons
LED displays are characterized by high brightness. If the brightness output of the display reaches 8000 CD /m2 in dark night, it will cause serious light interference.
The closer the distance between the observer and the display screen, or the larger the opposite Angle formed by the position of the observer and the display screen, or the more similar the direction of the observer's line of sight and the direction of the display screen, the more serious interference light will be generated.
There is a significant difference in ambient illumination between day and night, which results in the LED display with the same brightness producing different degrees of interference in different periods of time.
Observers of different ages, occupations, health conditions and psychological emotions will feel different degrees of interference light. For example, an observer who is often exposed to photosensitizers or suffers from eye diseases will be more sensitive to light.
Reason for content display
If the image content displayed on the display screen changes too fast, it will easily cause discomfort to the observer. Color brightness is too high, transition is blunt, also can cause eye discomfort.
Reasons for evaluation criteria
The display screen is applied in many places, such as road traffic, commercial area, residential area, etc. Due to the different nature of the place, the evaluation criteria of its interference light are also different.
Environmental conditions will significantly affect the interference of light on the display screen. If the environmental conditions are relatively bad, such as haze, dust, fog, rainstorm, wind and other weather, it will affect people's judgment of the interference of light on the display screen. Human eyes, under the influence of external factors, will cause inaccurate judgment standards and affect the objectivity of the evaluation.
The solution to the problem of LED display light pollution
The high brightness characteristic of LED display screen is an important cause of light pollution. In order to effectively solve the problem of light pollution, the following safety protection methods can be adopted.
1, rely on the environment to adjust the brightness
Adjust the brightness of human eyes comfortably
According to the ambient light intensity of the display, the overall brightness of LED display screen is adjusted to ensure the clarity of the display screen and avoid dazzling and glaring bad visual experience. According to the investigation, if the human eye is accustomed to the ambient brightness of 800 CD /m2, the brightness that the human eye can see is 80~ 8,000 CD /m2. Therefore, LED display screen should rely on the environment to adjust the brightness, and introduce the environment brightness monitoring equipment to provide a reliable basis for the brightness adjustment, so that the brightness of the display screen can be adjusted to the comfortable range of human eyes. During the night, the brightness of the display screen should be controlled at less than 10 times of the ambient brightness.
Introduce brightness adjustment standard
Many outdoor display screens are too bright at night, causing serious light pollution and affecting the lives of the surrounding residents to some extent. To this end, the relevant departments should introduce brightness adjustment standards for display screens, strengthen the prevention and control of light pollution, require display units to actively adjust brightness output according to the brightness of the environment, and strictly prohibit the output of high brightness and strong light in dark nights.
2. Cut blue light output
Light of different wavelengths will bring different visual perception to human eyes. Due to the complexity of human eyes perception, it is difficult to reflect human eyes' perception of light through the measurement standard of brightness. Therefore, irradiation quantity index can be introduced to judge the safe energy range of visible light. When measuring the effect of light on human eyes, the luminance perception of blue light by human eyes is not enough. Instead, irradiance measurement equipment is introduced to objectively reflect the influence of blue light output intensity on visual perception with the data measured by measurement equipment. LED display screen manufacturers to ensure that the display function on the basis of the appropriate reduction of blue light output, so as to avoid eye discomfort.
3. Control the spread of light
Reasonable arrangement of LED display light, within the scope of visual scale of human eyes, evenly distribute the output light energy of the display, to avoid local strong light problem of the display. This requires that the direction and scale of light irradiation must be strictly limited in the production of LED display, so as to effectively control the light pollution of LED display.
4. Express safety protection method
In the instruction manual of LED display products, precautions for safety protection shall be indicated, and the correct method of brightness adjustment of LED display shall be highlighted, and the possible harm caused by long-term direct eye contact with the display shall be explained clearly. If the display display brightness automatic adjustment system appears the operation fault, may adopt the manual adjustment way to carry on the brightness adjustment. At the same time, it is necessary to popularize the safety protection measures of light pollution to enhance the self-protection ability of the public. For example, if you cannot look directly at the display screen for a long time, try to avoid focusing your eyes on the details on the display screen, and avoid causing bright visual spots due to the concentration of LED in the fundus. In severe cases, it may even cause burns to the retina.
5. Improve product performance and quality
In order to ensure the performance of LED display screen products, it is necessary to strengthen the brightness detection of products in indoor and outdoor environment. In the process of indoor inspection, the staff should wear dark sunglasses with the brightness attenuation of 2 to 4 times, and observe whether there is any problem in the details of the display screen in a close range. In the outdoor detection process, the staff should wear dark sunglasses with a attenuation of 4 to 8 times. Especially in dark conditions, workers must wear safety tools to avoid exposure to strong light.
Introduce advanced technology
LED display screen in different time periods, different locations of the environment brightness changes significantly different. Once the brightness output of the display screen exceeds 60% of the ambient brightness, it will cause discomfort to the human eyes and generate light pollution. Therefore, the LED display screen should be equipped with an outdoor brightness acquisition system to collect the ambient brightness in real time and transmit the ambient brightness information to the central control room, which will automatically calculate the most suitable output brightness of the display screen according to the received data information and take it as the basis for brightness adjustment.
In addition, multilevel grayscale correction technology should be introduced in LED display to improve the stiff color transition of ordinary 8-bit color display, so as to avoid strong discomfort to human eyes. Under the support of multilevel grayscale correction technology, the color display level of the original display system can be raised to 14 bits, so as to bring soft color transition to the eyes and reduce the stimulation of light to the eyes.
Above all, LED display as a light source, it inevitably will appear in the process of running safety and light pollution, to effectively prevent the LED display the damage to human body, should be on the basis of comprehensive analysis of the safety light, take feasible measures to eliminate LED display light pollution, which in addition to being able to provide guarantee for human health, can provide help for the scope of application of broadening LED display.