eInk Screen Brightness Ranked!
In the mainstream display industry, screen technology and its specifications are, largely, well-documented. When buying a new phone, you can, with some degree of certainty, look up all the details, including those surrounding its display. How bright does it get (calculated in nits), how smooth is the motion (refresh rate or frames per second), how clear are the images (Resolution or PPI), the vibrancy of its colors, and the pixel technology used? All that and a whole lot more information is readily available and widely discussed. In contrast, the availability of eInk display specifications is almost nonexistent. The screen brightness, the effects of ghosting, actual refresh rates, and the brightness of the front light, to name a few, are all, virtually, unknown to the public.
DS62 Spectrophotometer
It's for this reason I wanted to find a way to quantify some of the things we observe with our eInk devices. But not just quantify them; I want to discuss them using established terms and standards. This way anyone with the ability to take the measurements will be able to verify all of the data I'm presenting here. To do this, I employed the use of a spectrophotometer, the DS62.
This device uses standard metrics, terms, and formulas to quantify a host of things, including Whiteness and Brightness—two of the most important parameters when talking about eInk screen quality. This way, we can discuss the readings more definitively. This also makes talking about these characteristics easier.
Black and White eInk screens (there are color ones, but let’s stick with B/W for this example) move tiny black pigment capsules around to display an image. Because of this fact, it makes sense to make the screen as white/bright as possible so that the black ink capsules stand out more against the background. This creates contrast. To reduce the dependence on light and reduce eyestrain, you would want that contrast to be as high as possible. A high-contrast screen could, potentially, be a major selling point for some consumers if they knew what those values were. There are other facets of the contrast discussion too, like “ghosting,” but I’ll cover that in another post. I also made a separate article explaining my methodology for measurement-taking with the DS62.
Now, let's look at the numbers.
This table shows us the perceived whiteness of the samples, sorted from whitest to blackest. The scale is from 0-100, where 0 is perfect black, and 100 is perfect white. For a control, I searched for whiteness tests on the Color Checker 24 and could not find any. This wasn’t too surprising, considering the fact that color charts aren’t typically used to measure whiteness. Since the whiteness of the color checker isn’t widely known, and the whiteness of loose-leaf paper varies, widely, I could not get a control sample for whiteness.
Later we will see that I was able to verify the Brightness measurements which gives me confident that my Whiteness measurements are accurate.
As we can see here, eInk devices fall short of the whiteness standard set by paper at 93.61 and the Spyder Color Chart (CHECKR 24) at 77.38. The closest the eInk devices I tested got to white is 48.09 (Viwoods AI Paper), which isn’t anywhere near paper-level whiteness at 86.76, but it’s leaps and bounds above the 19.45 of the reMarkable Paper Pro.
The surprise here, at least for me, is that the new Go 7. The screen looks to be visually whiter than the other devices but ranked 4th on the list of devices tested. Science FTW!
The control for the brightness test was the color chart, which allowed me to compare my measurements with other measurements taken on the Spyder Color Checkr 24. There was only one source I found that took brightness measurements linked here. The patch measured was the white patch, which is patch E1 on the chart. The measurements recorded were L=96.92, a=-0.47, and b=1.22. These values were very close to the ones I attained below, which let me know I was measuring the samples correctly and that my measurements were correct.
As we can see from this table, sorted by brightness, from highest to lowest, eInk devices fare far better. At 100, the sample would be reflecting 100% of the light around it. This would mean we can correlate these measurements to the percentage of light reflected. So, at best, the eInk devices I’ve tested reflect 72% (Viwoods AI Paper) of the ambient light around them. At worst, they drop to reflecting 55% of the ambient light (reMarkable Paper Pro). Not a bad showing at all, for eInk devices, considering Mead's writing paper is at 89%.
The Color shift data is also interesting. Here we can see a chart that shows each device’s “a” color shift values. These valuse are presented in order of display brightness.
Except for the Go 10.3, every device I’ve tested has a green shift, and in the case of the Tab Mini C, an extreme green shift, that actually shows up visually on the screen. Interestingly, the Go 10.3’s color shift towards red matches the degree of green shift in other devices.
Next up, we have the “b” color shift values that show us color shifts from blue to yellow.
Among the eInk devices I tested, the Go 10.3 and the reMarkable Paper Pro go against the grain here, with varying degrees of yellow shifts. This is in stark contrast to the typical blue shift you see with other devices. All the shifting towards blue seems obvious, now, considering paper also displays this shift towards blue. On the extreme end, we can see the expression of this data play out in the reMarkable Paper Pro’s slightly yellow screen, as it did in the Tab Mini C’s green-ish screen.
Lastly, we have a combination chart with both sets of color shift data (a/b) displayed at once.
This data is interesting for a few reasons. It shows that the Go 10.3 has the warmest color temperature screen of the bunch. It’s the only device on the list with positive values for both “a” and “b” color shifts. The most neutral color profile of all the eInk devices seems to be the Supernote Nomad. It has the lowest values (positive or negative) of any device. This indicates a very minimal color shift in any one direction.
This chart also gives us a color profile for paper and for what the color industry considers “white” (Spyder Color Chart). Based on that we can match up profile types. So, if you want a device that closely matches paper’s color profile, then you want a device with a negative “a” value, and a very positive “b” value. None of the devices I tested had that profile, but the Go 7 came the closest - Though I don’t recommend that device for writing. Want a device whose background closely matches the industry standard for white? Then you want a device with a negative “a” value and a positive “b” value, leading to the reMarkable Paper Pro. These are just examples, not recommendations, but you get the point.
So what does it all mean? Well, maybe nothing. But if you could choose the device with the brightest background to increase contrast and by extension visibility, would you? How much does a screen’s ability to match paper’s whiteness mean to you? If you could choose, would you rather have a device whose screen was slightly red versus slightly green or yellow? Does anyone want that info? I do.
