> It doesn't actually block that much light, all told?

It does. I'm using a dark theme for HN with a background of #222 and text of #CCC on my Dell U2412M display with the brightness at 100%. I measured with the ambient light sensor in my old Nexus 5 held up to my head. While lux values from smartphones are uncalibrated, it's the ratios that matter.

Dark theme, backlight 100%: 1 lux

Light theme, backlight 100%: 54 lux

Light theme, backlight 0% (not actually off): 7 lux

What is dark with backlight down? I'll try the lumen sensor when back at a computer. Where do you see the values?

And my hypothesis was more that the bright parts are still bright. It is obviously less overall, but the small things are still hitting your eyes. Potentially worse, as your eyes aren't dilated correctly for the brightness.

It reads zero from eye distance when dark with the backlight down. Here are readings from contact distance:

Dark 100%: 5 lux

Light 100%: 103 lux

Dark 0%: 0 lux

Light 0%: 14 lux

In my HDR mode settings, tuned for bright conditions, it is:

0% PQ: 0.12 nit

0% SDR: 0.2 nit

100% SDR: ~120 nit

100% PQ: 570 nit

It works better in dark mode than your low contrast. The screen does not support local dimming.

I missed what pq and sdr stand for. :(

Someone is going to ask for a wavelength soon, so get ready to calibrate for 450–485 nm :)

If anybody wants to buy me a spectrophotometer, I'd be happy to take measurements. Those things are pricey.

For my part, thanks for the measurements! I do intend on trying this when back at a computer. At face value, not seeing anything suspicious on these numbers. Bottom line, do not run a bright screen in the face. Darker colors do look to help, but so does dropping brightness. If worried about your eyes, do both.