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What is the difference with Flicker and Why is the Refresh Rate of LED Screens Important
Human eye involvement and Critical Flicker Fusion Frequency (CFF) in the Viewing of Outdoor Digital Displays
As the pulses of light increase above the Critical Flicker Fusion Frequency, the human eye perceives the light as a constant.
In Digital Outdoor Advertisement (DOOH) displays, Critical Flicker Fusion Frequency is not constant and is affected by the speed of the motion of content, the light of the environment, and the distance of the viewer from the display.
Billboards that are not digitized seem to be stable with low refresh rates, however, a display that is a video wall must have a higher refresh rate in order for the flicker not to be visible. A research conducted by The Vision Council in 2023, stated that 15% of the viewers experience eye strain from observing displays operating below 60Hz. This confirms the importance of refresh rate to visual comfort. The most important factor of Critical Flicker Fusion Frequency (CFF) is the reason why low refresh rate displays are perceived as not stable. When watch displays with low refresh rate, our visual system is able to perceive the display at the same frame rate that the display is being refreshed and therefore able to perceive the low refresh rate, especially when making a rapid eye movement or observing a high contrast environment.
What are the factors that lead to the perception of Flicker on Outdoor LED Advertisement Displays due to Ambient Light, Distance of the Viewer and Motion of the Content
All three factors that are outlined lead to the further reduction of the Critical Flicker Fusion Frequency on outdoor displays.
1) Ambient Light: Increase in ambient light leads to pupillary contraction which increases Retinal contrast sensitivity and hence increases the perception of Flicker. A LED screen that is below 3,000 nit specification will need to have a higher refresh rate to keep in stable in the presence of bright light.
2) Viewing Distance: When the outdoor LED displays are large in size and when the pixels are larger, the distance of the viewer leads to perception of flicker as a result of inconsistent refresh due to larger pitch in the pixel dimensions and larger distance in viewing angles.
3) Motion of the Content: Flicker becomes more pronounced especially in frame gaps when there is scrolling text, fast moving video or live sports and event coverage. This is more so when the display refresh rate is below 3840Hz.
There are countless examples where a 1920Hz screen will work without fault indoors but will even look like it is flickering when placed in direct sunlight and playing sports-related content. This isn’t a fault with the screen. This will showcase the adverse effects that the environment has on the comprehensive abilities of the human eye to fuse frames.
Flicker-Free Thresholds: From Minimum Viable to Broadcast-Grade LED Advertising Screens
1920 Hz: The IEEE 1789-2015 baseline for perceptually flicker-free LED advertising screens
Boston: April 2017 The IEEE 1789-2015 standard defined 1920 Hz as the absolute minimum standard for flicker-free operation for LED screens with advertising content when viewed under static, normal conditions. This is the minimum standard that exists today adopted by the industry based on years of research to determine the photobiological safety of LED screens based on human visual persistence. The issue is that this standard is for static, indoor, controlled environments, and not for complex and demanding environments. In high-brightness outdoor environments where there is 100,000 lux of ambient light and high motion content, 1920Hz is too low: IEEE’s own study of this in 2023 found that 18% of viewers reported discomforting visual stimuli under those conditions. For LED screens with static content, 1920 Hz is still a standard, but there is not enough ‘headroom’ for it to be used on a ‘sophisticated’ level’ with dynamic content, scrolling ads, and capturing viewer engagement while in transit applications.
3840 Hz and beyond: Ultra high refresh rates and their impact for dynamic outdoor LED advertising screens
3840 Hz is becoming the performance threshold for outdoor LED advertising screens. The integration of high refresh rates LED screens, high definition video, and advertising is ideal for high dwell time and high traffic venues. Other use cases are high brightness advertising screens at transportation hubs, stadiums, and urban retail. Using DisplayDaily independent testing, hehighir frequencyevidenctively Hammfurctured a 94% in positive viewer perception for lower visual fatigue LED screens of 1920 Hz versus higher rates LED screens in fast motion video. We anticipate the use of high refresh rates advertising screens at sports events for live broadcasting and for futsal goal video broadcasting. The lower goal post camera shutter speeds in conjunction with refresh rates facilitate perfect frame sync in higher Hz broadcasts. We also anticipate positive advertiser return on investment based on the Digital Signage Federation 2023 ad report of 22% uplift in advertisement content recall at 3840 refresh rates. We also have the ability to add agile advertising in-freight passenger transport with the advertising content, and have high refresh rate video for agile advertising depending on other and fast volleyball to be the main badminton. It also offers the ability to put on access soccer goals.
Camera Capture Compatibility: Removing Artifacts from Media-Integrated LED Advertising Screens
Shutter speed artifacts: The 1920Hz limit with most professional cameras
When capturing LED advertising screens for videos intended for TV, social media, or influencer marketing, 1920 Hz frequently causes undesirable artifacts during recording, including rolling black bands, strobing, or changing brightness. This is due to the fact that most professional cameras use shutter speeds of 1/500s to 1/2000s to freeze motion—and at 1920 Hz, there is an ~0.5ms ‘off’ period during each refresh cycle where the LEDs are unlit During that shutter window, the camera records the absence of light. Testing has verified the presence of artifacts in 78% of recordings when shutter speeds are above 1/1000s. This unavoidably makes 1920 Hz unfit for any media capture focused advertising campaign.
3840 Hz is the new standard for social media optimized and broadcast ready LED advertising screens.
At 3840 Hz, the off period is only 0.25ms. This is faster than most professional shutter speeds. This means that LEDs are perceptually 'on' for the entire exposure time. This means that there will be no banding artifacts even with shutter speeds of 1/4000s. Independent testing confirms that 3840 Hz screens are artifact free in 98% of use cases, from filming social media stories with smartphones to filming with 4K cinema cameras. This is why 3840 Hz screens are the new standard for media integrated out of home advertising. Advertisers no longer have to worry about content pacing or lighting when filming. Filmmakers no longer have to worry about unpredictable artifacts disrupting the high quality and resolution of their work.
Practical Verification: Confirming the True Flicker-Free Performance of an LED Advertising Screen
The first step is a hands-on approach: the LED screen specs say it is flicker-free, but how can we know? Try the smartphone camera test. Set the screen to maximum brightness and step outside. Record a video with the default camera settings. If there are rolling bars, pulsing, or the screen is otherwise flickering, the screen refresh rate is probably higher than the IEEE 1789-2015 standard (> 1920 Hz). For a more in-depth analysis, use an oscilloscope to capture the LED driver signal. True flicker-free drivers will have consistent timing pulses at the rated frequency, and will not distort under thermal load. Finally, the ultimate test: an in screen. Set the screen to 85% brightness and keep it in Daylight. Monitor the screen for 48 hours for any pixel defects, brightness drift, regular or irregular dimming of segments: any form of driver instability. This test will ultimately determine if the manufacturer's claims are true. Flicker-free advertising will ensure visual comfort for your audience.
FAQ
What is the Critical Flicker Fusion Frequency (CFF)?
CFF is defined as the threshold at which a light is perceived as a constant source of illumination rather than discrete light pulses. The CFF is not constant: it can change depending on motion of the light, ambient light, etc.
What is the refresh rate in LED advertising screens?
Refreshing is the ability of an LED advertising screen to change images. High refresh rates will lead to the absence of flickers, while lower rates can make LED advertising screens visibly flickering.
What is the optimum refresh rate for an outdoor LED screen? The recommended refresh rate is at least 3840 Hz for high quality outdoor LED display screens. This refresh rate completely eliminates the screen flicker and fluidly displays fast-moving images.
What is the influence of ambient light on flicker?
In bright environments, especially those with ambient light, flicker is even more evident. This is attributed to the ambient light increasing the contrast sensitivity of the retina. It, therefore, calls for higher refresh rates so that flicker is less apparent and more stable.
How would you evaluate screen flicker?
A smartphone camera test, performance testing with waveform analysis tools like an oscilloscope, and screen evaluation under various stress conditions for 48hr would be appropriate.
