CCTV 315 Gala complained that mobile phone detection LED lights are unreliable
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Last night's 315 party announced such a small experiment, using a simple mobile phone camera to determine whether a table lamp flickers and hurts the eyes. Before the party was over, the water army of a certain domestic company began to take action. Some companies that took off their pants directly issued such an article "Why can XX mobile phones test light bulb flickering". EXO me? As Lao Yang who is not naked yet, I have to tell you responsibly that this matter is not particularly reliable. Why does the light flicker? The answer is very simple, that is, China's household electricity is 220V 50Hz alternating current. Let's highlight the key points, alternating current! Electricity! Let's review the junior high school physics class with former academic master teacher Yang. First of all, the generation of current is through the conductor in the magnetic field, moving in a direction perpendicular to the magnetic flux lines, and the internal current is generated. This principle was discovered by British scientist Faraday in 1821. In the early days, because people had not thought of any particularly advanced methods, they used the method of converting mechanical energy into electrical energy to make generators, that is, the energy generated by the movement was processed into electricity. But if the magnetic field is made parallel to the positive and negative poles, and the conductor runs from the left to the right, the electricity will be gone. It is more complicated to go back and re-do the mechanical design. So later generations transformed the generator into a shape that rotates around the center. According to the physical structure of the generator, the voltage is actually a sine wave. When the resistance is constant, the current becomes a wave. Then the light bulb uses current to convert electricity into light. When the current is large, the light is bright, and when the current is small, the light is small, which causes the flicker of the light. Why does flicker hurt the eyes? Didn’t I just say that China commonly uses 50Hz alternating current? What is the concept of 50Hz? It means 50 positive and negative changes in one second. The brain’s recognition of changes is not noticeable above 30 times per second, and you look like it is always bright. But for sensitive eyes, this flickering effect will make the pupils grow and shrink, so the muscles that control the pupils will be exhausted. Since muscles always have to work, the intensity of labor is also very different. For example, if you lift a 10KG dumbbell and a 1KG dumbbell 100 times in the same minute, the feeling of tiredness is also different. So in order to make the eye muscles less tired, the amplitude of light changes should be reduced as much as possible. The so-called eye protection lamps on the market are trying their best to control the amplitude of the light brightness change. The exact name of the so-called flicker-free lamps on the market is "imperceptible flicker". The current technology cannot achieve large-scale commercial use of completely flicker-free light sources, and the price is still about 100 yuan. Is it reliable to use a mobile phone for testing? At the 315 Gala last night, CCTV revealed that many table lamps that claim to protect eyes actually do not meet the standards. It was demonstrated on site that it can be displayed through the current mobile phone camera interface. This is actually a simple method, but not so accurate. At present, the CMOS photosensitive elements used in most mobile phones on the market use progressive scanning. That is, the light intensity sensed by the first line is first temporarily stored in the form of data, and then converted and stored in the second and third lines. But conversion and storage take time. When the second line is recorded, converted and stored, and in the super short time when the first line switches to the second line, the brightness of the lamp has actually changed. By analogy, the brightness is different when recording each line, but the change of light brightness is periodic, so the phenomenon of light and dark texture in the final image is caused. There is another condition for this phenomenon to occur, that is, the shutter speed must be less than the cycle of a light and dark change of the bulb, that is, less than 1/50s. For current smartphones, the default shutter time and other shooting parameters of the camera app are automatically set according to the ambient brightness. It is possible that the shutter time is longer than 1/50 second by default. Manufacturers have also recognized this interference problem, so many companies now use software and hardware and other algorithms to avoid this light and dark pattern that interferes with image quality even in the manually adjustable shutter speed mode. Then the final conclusion is that it is possible that this desk lamp is not qualified, but your phone happens to have a longer shutter time or is automatically optimized. It is not very comprehensive to use this method to measure whether the bulb is stroboscopic, and it is even more ridiculous to use it to measure the pros and cons of a mobile phone camera. So how to choose a desk lamp that really protects the eyes? I'm sorry to tell you that Lao Yang doesn't have any particularly civilian measurement methods. Because in addition to flicker, light uniformity, blue light, etc. are also the culprits of eye damage. Color temperature is also one of the factors that affect the user experience. What's more annoying is that this matter varies from person to person. However, since those who do a good job in controlling flicker, blue light, and light uniformity generally have high requirements for craftsmanship and technology, they are usually not cheap. The more expensive one is, the higher the chance of meeting the standard... In addition to desk lamps, some lower-end monitors including TVs, computers, and mobile phones will have screen flicker problems. Although flicker will put pressure on the eye muscles, it is actually more important to maintain good eye habits, including correct sitting posture and regular rest habits. As a winner of Toutiao's Qingyun Plan and Baijiahao's Bai+ Plan, the 2019 Baidu Digital Author of the Year, the Baijiahao's Most Popular Author in the Technology Field, the 2019 Sogou Technology and Culture Author, and the 2021 Baijiahao Quarterly Influential Creator, he has won many awards, including the 2013 Sohu Best Industry Media Person, the 2015 China New Media Entrepreneurship Competition Beijing Third Place, the 2015 Guangmang Experience Award, the 2015 China New Media Entrepreneurship Competition Finals Third Place, and the 2018 Baidu Dynamic Annual Powerful Celebrity. |
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