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Are humans more adapted to “light mode” or “dark mode”?

Are humans more adapted to “light mode” or “dark mode”?


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I was discussing with a colleague about using dark-mode vs. light mode and remembered an article arguing that humans vision is more adapted to light-mode rather than dark-mode:

I know that the trend “du jour” is to have a dark mode for pretty much everything, but look around the world is not dark with a bit of light, it's actually the contrary. And as the human has evolved its vision to adapt to this reality, it's asking extra efforts on many people.

Unfortunately, no reference is provided to support this claim, so I am wondering if this is just an opinion or there are some studies to support this.

Wikipedia seems to confirm this somewhat since we are adapting much faster to "light mode" transition than to dark mode one:

This adaptation period is different between rod and cone cells and results from the regeneration of photopigments to increase retinal sensitivity. Light adaptation, in contrast, works very quickly, within seconds.

Also, some studies confirm that working using light mode is on average more efficient than using dark mode:

light mode won across all dimensions: irrespective of age, the positive contrast polarity was better for both visual-acuity tasks and for proofreading tasks.

I am looking for arguments coming from evolutionary biology to confirm (or not) the assumption that human evolution favors light mode.


A question that requires quite a lot of guts to ask on this site :) Nonetheless, and risking sparking a debate, there are a few arguments that spring to (my!) mind that can support the notion that we thrive better in 'day mode' (i.e., photopic conditions).

  • To start with a controversial assumption, humans are diurnal animals, meaning we are probably, but arguably, best adapted to photopic (a lot of light) conditions.
  • A safer and less philosophical way to approach your question is by looking at the physiology and anatomy of the photosensitive organ of humans, i.e., the retina. The photosensitive cells in the retina are the rods and cones. Photopic conditions favor cone receptors that mediate the perception of color. Scotopic (little light) conditions favor rod activity, which are much more sensitive to photons, but operate on a gray scale only. The highest density of photoreceptors is found in the macular region, which is stacked with cones and confers high-acuity color vision. The periphery of the retina contains mostly rods, which mediate low-visual acuity only. Since highest densities of photoreceptors are situated at the most important spot located at approximately 0 degrees, i.e., our point of focus, and since these are mainly cones, we apparently are best adapted to photopic conditions Kolb, 2012).
  • An evolutionary approach would be to start with the fact that (most) humans are trichromats (barred folks with some sort of color blindness), meaning we synthesize our color palette using 3 cone receptors sensitive to red (long wavelength), green (intermediate) and blue (short). Humans are thought to have evolved from apes. Those apes are thought to have been dichromats, which have only a long/intermediate cone and a blue cone. It has been put forward that the splitting of the short/intermediate cone in our ape ancestors to a separate red/green cone was favorable because we could better distinguish ripe from unripe fruits. Since cones operate in the light, we apparently were selected for cone activity and thus photopic conditions (Bompas et al, 2013).

Literature
- Bompas et al., Iperception (2013); 4(2): 84-94
- Kolb, Webvision - The Organization of the Retina and Visual System (2012), Moran Eye Center

Further reading
- Why does a light object appear lighter in your peripheral vision when it's dark?


From experiments it seems you should better use dark mode if you want to prevent myopia:

Using optical coherence tomography (OCT) in young human subjects, we found that the choroid, the heavily perfused layer behind the retina in the eye, becomes about 16 µm thinner in only one hour when subjects read black text on white background but about 10 µm thicker when they read white text from black background… Therefore, reading white text from a black screen or tablet may be a way to inhibit myopia, while conventional black text on white background may stimulate myopia.

So although humans are commonly awake during the day and sleep at night it seems that this fact is actually irrelevant when it comes to the effects of dark/light mode for the health of your eyes.


Both.

More specifically, we're a kitbashed light-mode version of a primarily dark-mode group of animals. Mammals famously have terrible color vision, most mammals are dichromats (red color-blind) whereas most other animals like fishes, amphibians, reptiles, and birds are trichromats or even tetrachromats (seeing into the ultraviolet spectrum). In their evolution mammals got rid of a lot of their cones and replaced them with rods, giving them much better dark vision at the expense of not being able to see good colors. But this was back in the Mesozoic, when most mammals were nocturnal, crespuscular, or burrowing, and color vision wasn't a huge deal.

Primates then re-evolved color vision by duplicating and repurposing a cone for green some time in the Eocene. It is thought that they did this because it helps in identifying ripe fruits, which are often some shade of red, orange, or yellow, from green unripe fruit. We also lost our tapetum lucidum, which is the reflective layer of the eye that you see when shining a light in most animal's eyes that greatly enhances night-time vision. No one knows why, it may be genetic drift. Unfortunately our color vision isn't great, so we're kind of stuck in this awkward intermediate between other mammals, which can see great in the dark but have no color vision, and birds and reptiles, which have amazing color vision but are borderline blind in the dark (owls being the obvious exception).



Comments:

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