What They Say
An article in IEEE Spectrum highlights issues with OLED display flicker. Tekla S. Perry upgraded from an older iPhone SE to an iPhone 12 Mini as the smaller display was appealing. However, on firing up the phone, discomfort set in. Her tests established that the problem got worse at lower levels of brightness, suggesting that PWM dimming might be causing a problem. By using maximum brightness, text was tolerable, but she still felt feelings of discomfort when viewing photographic images.
A test of using an iPhone SE with an LCD saw the discomfort go away.
Perry spoke with our friend, Ray Soneira, who said that has had ‘hundreds of inquiries over the years regarding this issue’. He explained some of the range of system issues involved in how the flicker can be caused.
What We Think
At one time, I spent a lot of time on flicker issues, but that was back in the days of CRTs. However, CRT phosphors had a relatively long persistence effect compared to today’s OLEDs. In those days 70Hz was reckoned to be flicker-free for 90% of people. However, as someone that spent a long time looking at and becoming aware of flicker, I was convinced that, over time, I got more sensitive to flicker. Initially, I wasn’t really aware at even 60Hz, but in later times, I needed a much higher frame rate, or the flicker became oppressive.
Once LCDs came along, the problem basically went away (although you could get PWM flicker at very low brightness – leading companies that wanted to develop displays for very low brightness – e.g. maritime applications – that had current-based control of brightness rather than using PWM).
Over the years there has been a lot of work on the ‘critical fusion frequency’ or CFF of human vision – which is the point at which humans do not see flashing or separate images, but a steady image. However, there are many, many variables including the luminance, contrast, angle of view (peripheral vision is more sensitive, typically), colour, frequency and mark/space ratio (the balance between the time on & off when PWM is being operated) which makes complete characterisation tricky. (BR)
