I know that certain animals have the ability to see in darker areas but not in pitch black due to a special ability they have in their eyes which also gives them that glowing effect. Could elves have the same thing?


Possible in fantasy, but of dubious utility

The tapetum lucidum is a reflective layer behind the retina, which gives a second chance to the photons which were not intercepted on their first pass. It increases light sensitivity by about 44% or 0.5 f-stops (an ideal tapetum lucidum would increase sensitivity by 1 f-stop); the catch is that is decreases acuity, because the image is blurred.

As for realism, while most primates don't have a tapetum lucidum, most primitive primates (strepsirrhines) do. If elves do indeed have a tapetum lucidum then they must have diverged from our evolutionary line about 65 million years ago.

Humans have very decent night vision for a diurnal animal; whether the increased light sensitivity is worth the decrease in acuity depends on the life strategy of those elves. Are they nocturnal animals? The elves in the movies looked like civilized people, don't they have lamps?

(As an aside, the maximum aperture of the human eye, dark adapted, is about f/2.1, which is very good; but only about 10-15% percent of the retina is occupied by the rod cells responsible for scotopic vision. When completely dark adapted, with a bit of luck human eyes can detect individual photons; bursts of twenty or so yellow-green photons can be detected quite reliably. The catch is that switching from photopic mode to scotopic mode takes several minutes; the reverse transition is much faster, taking only a few seconds.)

So what else can I do?

If you really want your elves to have significantly better night vision than humans, then you have two avenues open:

  • Give them bigger eyes.

    Low-light image quality scales with sensor size. This is the a fundamental reason why a full-frame camera with its 864 mm² sensor (or even an APS-C camera with a 384 mm² sensor) takes much better low-light pictures than a compact or mobile phone camera with a 28 mm² sensor. After all, low-light sensitivity is limited by the number of photons which fall on the sensor, and this is proportional with sensor area.

  • Give them more rod cells.

    Humans have many more cone cells (responsible for day vision) than rod cells (responsible for night vision). Increasing the proportion of rod cells will increase low light sensitivity, with a corresponding reduction in visual acuity in day time.

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  • $\begingroup$ Huh. Greater rod density would lead to colourblind elves... $\endgroup$ – Joe Bloggs Aug 26 '17 at 17:50
  • $\begingroup$ @JoeBloggs: No, just to elves with lower visual acuity. Rods don't work in photopic vision at all. (The eye operates as if it were a photo camera with two overlapped / intermingled sensors, one color but low sensitivity and one highly sensitive but black-and-white.) $\endgroup$ – AlexP Aug 26 '17 at 21:02
  • $\begingroup$ Precisely. I'm assuming that greater rod density also leads to more of the eye being made up of rods (a fixed amount of energy being spent on the eye), which would (by necessity) lead to fewer cones, which would lead to lower ability to detect and differentiate colours. I'll grant that's not the medical definition of colourblindness, but the effects would be similar enough to be interesting. $\endgroup$ – Joe Bloggs Aug 27 '17 at 7:56
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    $\begingroup$ Pedantic photography note: 0.5 stops, but not f-stops — the latter is just for aperture in relation to focal length. photo.stackexchange.com/questions/15706/what-is-one-stop $\endgroup$ – mattdm Jun 21 '19 at 0:10
  • $\begingroup$ @AlexP I'd take the latter avenue, as the first one reminds me too much of Alita. $\endgroup$ – JohnWDailey Feb 25 at 20:25

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