the led LED Backlight Flicker in LCD Displays

by:Leimove     2020-03-04







































What is the reason for the LCD display flashing?Computer monitors have grown from bulky, Bulky CRTs to today's stylish, modern LCD.Up to now, one of the most significant improvements in display technology is LED backlight, which can achieve brighter, clearer images while reducing power consumption.The manufacturer emphasizes the benefits of the led relative to the old CCFL (fluorescent) backlight.However, some people will encounter problems such as unusual eye fatigue, pain, or headaches that seem to be caused by their new monitor.The most likely culprit is the flashing of LED backlight."But wait," you might say, "I thought the LCD display should flash --free!\".In fact, while the CRT display redraws the entire screen multiple times per second (determined by refresh rate), the LCD display provides a constant image that simply changes the pixel color from one to the otherThe speed of this process depends on the response time of the monitor, which is different from the refresh rate.Therefore, the source of the flashing of the modern LCD display is not the LCD matrix itself, but the backlight.In the LED display, the brightness when flashing is reduced by 100% because the backlight dimming method is called PWM (pulseWidth modulation ).In many cases, when the laptop is running on the battery power supply, the PWM will start up even at the maximum brightness to save energy.The CCFL display also uses PWM, but the resulting flicker may not be obvious compared to the ledFor more information about below.How does PWM work in LED LCD?More information about pulsesPulse-Width modulation (PWM) is a technology for dimming the backlight of the LCD.It includes turning on and off the backlight faster than the human eye can see.Once you reduce the brightness setting on the display from the maximum, the PWM dimming will begin.Compared to analog dimming that provides continuous lighting, it has many advantages: PWM is cheaper to implement, wider to adjust range, and prevents discoloration under lower brightness settings.So if PWM-Darkening LEDs are great, do they really cause problems like extra eye fatigue or headaches?After all, humans cannot see the LCD backlight flashing with the naked eye.Of course, if the PWM switching frequency is used high enough,Such as 500Hz-Even the most sensitive people should not be affected.However, many LCD displays on the market today seem to use backlight frequencies between 100Hz and 200Hz.At this frequency, humans are still unable to sense the turn-on and off of the backlight cycle, but that does not mean that this led pwm flashing will not hurt their eyes or affect their nervous system.According to the study, 1 out of about 4,000 people in the range of 3 to 70Hz is very vulnerable to the flash...What is not well known is long-Prolonged exposure to higher frequencies of flicker (within the range of 70-160Hz) can also lead to discomfort, headaches and visual impairment.http://www.digikey.Com/us/en/techzone/lighting/resources/articles/representation-and-minimizing-led-flicker.There is good evidence that light signal fluctuations detected by the nervous system can be as high as 200Hz.http://grouper.ieee.Org/groups/1789/public.Physiological evidence from humans and monkeys suggests that the flicker rate beyond the threshold of the perceived critical flicker frequency can still produce visual responses in the cortex and cortex.Martinez-Conde, S., Macknik, S.L., and Hubel, D.H.(2002).Proc Natl Acad Sci, 99, 13920-13925.Different points in the visual system have very different sensitivity of critical flicker fusion rate (CFF.There are different signal integrations for each cell type.[...Some retina cells can maintain a discharge rate of up to 250Hz.http://www.bio.Net/bionet/mm/neur-sci/2007-July/061925.You can find more links to this topic later on the page.This video shows the LED backlight of the MacBook Pro and flashes 40 times slower, so you can see what's going on when you dim the brightness on the LCD screen.This video was taken by TFTcentral with a high-speed camera.co.uk crew.You might wonder why people who have never had a problem with CCFLNow the backlight screen complains that their new LED display or TV has hurt their eyes.CCFLs in LCD panels also use PWM dimming, so why don't they cause the same problem?There are two main reasons for this.First of all, the LED can be turned on and off almost immediately, but even if it is powered off, the fluorescent lamp will glow briefly, providing a smoother transition between the "on" and the "off" states.The second reason is that the WLED backlight is often much brighter than the CCFL back.Not only does this mean that more people will use a lower brightness setting (thus increasing the flicker), but the difference between the "on" and the "off" states is also more obvious.After all, during a short period of darkness, your backlight emits a full-bright pulse.There is a way to see the effect of low-frequency PWM in the LED backlight with the naked eye.Simply set the display to the lowest possible brightness and wave your hands, fingers or pencils in front of a white background.If the object is sharpDefined edges, the backlight works at a fairly low frequency.If the edge is blurry, then your monitor either uses a constant current dimming or a high-frequency PWM that cannot be detected by the human eye.Share your experience with LED backlight in modern displays and TVs.Do you experience any additional eye fatigue when using the LEDbacklit LCDs?Flicker-Free, No-If PWM-Dell ultra harp U2414H is one of the brand new LED productsBacklight Displays that do not use PWM dimming, as TFTCentral tested using an oscilloscope.In other words, it uses a constant control backlight and is worth getting a real "flicker-Free LCD display.Other benefits include an IPS matrix with excellent image quality, fast response time, and low input lag, as well as a thin border.The minimum brightness measured is slightly higher than 32 cd/m2, which means that you can dim this monitor to almost nothing and use it comfortably in a dark room.prad.It could be the first site on the Web to present the topic of the LCD monitor PWM switch, as well as potential issues related to this approach.Their advice to the manufacturer is to increase the PWM frequency to at least 250Hz, or to use other dimming methods that do not generate flickering at all.TFTcentral.co.Detailed articles about pulsesWidth Modulation in LCD display.They provide many excellent illustrations and include instructions for measuring the backlight PWM frequency of the display using a digital camera, and you can do it yourself without any complex equipment.A computer enthusiast, he refitted his LCD display using a normal incandescent lamp as a backlight.His page has a lot of information about the screen flashing theme, as well as a lot of other people's testimonials of eye fatigue, pain, stress, migraine and other problems when using the digital screen.He also talked about the potential problems of fluorescent lighting.(Note: The web page is no longer available, so the link causes a copy at the time of the archive.org).If you know any other interesting and useful articles about this topic, please mention them in the comments below.
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