Help wanted to measure flicker and/or test a flicker-free monitor

I found a monitor today that has very low flicker. It's an LG 27MQ450-B. I paid $130.

My hypothesis, of course, is that I can use this monitor without headaches since the flicker is so low. It comes with a 30 day return policy, so I'll use it for a couple weeks and let you know what I think.

If it works well, I'll buy a handful of these, test them with my setup, and re-sell them at cost. Hopefully some of you will participate in this experiment.

Here are some screen shots. All screen shots are at 100x magnification.

Flicker at contrast setting of 40 and 100% brightness. This is the setting I plan to use

Same as above, except the contrast is set to 100. Interesting how the shape of the flicker changes with a higher contrast. This setting is roughly twice as bright as the previous setting.

Same as above, except the contrast is set to 0. This setting is about 1/3 as bright as when the contrast is set to 40. This is a bit too dim for me.

Also interesting: when I adjust the color settings, it changes the shape of the flicker. The default for this monitor is for R G and B to be at 50, but this screen shot has them all set to 100. Contrast is set to 40.

AlanSmith I bought the radex lupin a few years ago. I found it helpful, but the the photodiode + oscilloscope was much more useful for me because I could see the shape of the graph, rather than just a percentage. For instance incandescent lights flicker, but it's a very smooth, gradual flicker (like a sine wave).

I do get headaches and tinnitus from the flickering of pixels, but I wouldn't say that my eyes hurt.

I can use a 6bit panel, but I generally use Intel integrated graphics which I don't think uses temporal dithering by default (I believe the default is spacial dithering, which doesn't bother me).

Bright screens bother me if they're excessively bright, but for me I don't need to turn the brightness all the way down to 0.

AlanSmith The problem with Laptopmedia is they only test for PWM, and for me, PWM is only part of the problem.

JTL I read a couple places that this monitor supports 167 colors. I assume that means 167 out of a possible 256. So I assume it would dither (temporal and/or spatial) to get those 89 missing colors. Another site said it uses 8 bit + FRC.

That said, my light meter can't detect any flicker caused by temporal dithering. I've tested 100+ shades of gray, red, green and blue. I'm not saying there isn't temporal dithering, but any decent* temporal dithering algorithm would be very difficult to detect with a light meter.

Personally, I believe things like backlight flicker (not just PWM), OLED refresh cycles, pixel inversion and other pixel flicker are more likely to cause headaches because those things are detectable with a light meter. I don't think temporal dithering (or spatiotemporal dithering) will cause me headaches as long as it uses a decent algorithm. The flicker is so much smaller for temporal dithering than it is for those other causes of flicker.

* I did use Ditherig to turn on temporal dithering for my laptop and on certain shades of gray the screen literally flickered from one shade to another and the flicker was visible (both with the naked eye and on my light meter). I'm assuming that most decent dithering algorithms use spatiotemporal dithering and are more intelligent about randomly spreading the use of adjacent colors through space and time.

qb74 I'm using a Picoscope 2204a. All the oscilloscope settings can be found in the screen shots above. the only setting you cant see in the screen shots is the gain/zoom, which is generally 100x.

I get really clear waveforms at 100KHz. The specs say it handles 10MHz, but I haven't seen any displays (backlights) that flicker faster than 100KHz.

One nice thing about the thorlabs sensor is that it has a circular shield around the photo cell that eliminates all light from the surrounding environment when the unit is placed directly on the screen. I thought I might need to test in a dark environment, but I found that to be unnecessary.

By the way, I've had a lot of headaches/tinnitus recently so I'm waiting for a day that I don't have headaches to give the new monitor a thorough test. I used it for a couple hours on Sunday. I began with a slight headache and ended with a slight headache, which really doesn't tell us much (other than that the monitor isn't absolutely horrible).

Also, I forgot to mention that I bought the monitor at a place called MicroCenter which literally has about 50 monitors on display. I had previously gone to a couple different Best Buy locations that have about 15 monitors on display. The monitor I purchased was the only monitor I found that was 27" or larger with little to no flicker. I found a couple 24" monitors with little to no flicker. So percentage-wise, you could say that roughly 5% of monitors (3 out of about 65 or so) have little to no flicker.

jen does your system allow you to measure the flicker of subpixels of different colors separately? If so, have you noticed any correlation with symptoms if there’s more color-to-color flicker?

I found something fascinating on your site: "It turns out that on every screen I've tested, Nightshift works by flickering green subpixels somewhat more and flickering blue subpixels a lot more, thus reducing the average amount of green and blue light. The overall effect is to create much more color-to-color flicker, since the screen flickers between very red and somewhat more blue/green."

I never knew why nightshift bothered me. I have lent my equipment to a friend, but I'll take a look when I get it back. I can isolate the red/green/blue subpixels using this page, which has all 256 shades of gray, red, green and blue.

The subpixel flicker mentioned on your site is what's called pixel inversion. I created this site (https://pixelinversion.com) to help visually see this flickering without a microscope. I can detect the pixel inversion flickering with the Thorlabs PDA100A2 (which has a gain/zoom feature) but I was not able to detect it with my homemade photodetector.

I see that a lot of your work has been on lightbulbs. I'm super-happy with some MaxLite bulbs that I bought that have a completely flat waveform. For testing lightbulbs with a photodetector, I've just bought a color lens filter kit so I can see the waveforms of the different colors. I'll test that as well when I get my equipment back.