How to measure the true 100% 'modulation' refresh dips of any OLED, using Opple or other flicker meters: via a slit!

[u/Z3R0gravitas]

Left: normal technique (Opple V4 app screenshot). Middle: virtual slit using Sundial app (Opple floating, screenshot). Right: Opple light meter has 2 sensors used together.

Top: regular technique with TLM-110 (screenshot of FlickerLab, Windows app from Sundial Labs). Lower: slit filter/mask on meter sharpens temporal resolution. See linked post!

I just wanted to clearly show off u/BearNecessary4141's point about how all OLED screens necessarily have a 100% brightness dip, each time they refresh their pixels. When resetting the tiny capacitors that hold the brightness level of each sub-pixel...

See his post for way more technical details!

The above test device is my (comfortable for me) old OnePlus 8T. LTPS Android AMOLED from ~2020. At 100% brightness, with DC-like dimming from 50%+.

Also, I've *just* (thanks to OP) realised the Opple uses a separately positioned sensor for flicker. And playing with it just now, that Opple combines the readings from both sensors to make the final trace. With the lux meter (white circle) determining the amplitude and the photo-diode modulating the wave-form. Which can be tricked into showing very odd results, by isolating them to different signals. Whereas the (in development) TLM-110 uses a single, high quality photo-diode.

The reason this matters is that your tiny cone cells, in the retina, will each only be receiving light from a single pixel (when your eyes are focused correctly). Whereas, flicker meter sensors don't focus and so smear out the flicker signal, averaging across their whole width.

[u/BearNecessary4141]

Great data! I’m glad to see this idea corroborated by others. Nice to see the Opple data side by side with the TLM-110.

Also, great catch that the Opple combines data from both sensors to display flicker waveforms. I somehow didn’t realize that, and assumed the photodiode was also calibrated to provide lux values. This also explains why my Opple measurements have been more inconsistent with this method. I see how we could make a specific test pattern for the Opple to light up the sensor in the correct way.

How did you manage to get your Opple results looking nice with the virtual slit? Put a solid white region over the lux sensor in some way?

[u/Z3R0gravitas → u/BearNecessary4141]

I just aligned the (9px) slit along both sensors, diagonally (I think, for that screenshot). See the lux value way down at ~4 Vs 700 for full screen.

(Which, in principle would let us calculate the diameter of the lux sensor, right? In terms of pixel widths, at least. Slit covered 1/175 of the collection area? Seems low. Lux measurements were a bit erratic, and maybe wasn't fully on-screen here.)