The question is fairly straightforward but to put a bit of context:

(Slice of life): I've often noticed how even though my eyesight really isn't great* I still somehow manage seeing a lot better at night than most people. I've often wondered why that is...
*(myopia, dry eyes, add laser surgery and myopia again 'gah')

In a fantasy/sci-fi world I'm currently working on, a civilization lives near a very bright star. My idea is that this civilization evolves to preserve eyesight by almost blinding itself from the light of the star (see it as a kind of biological super squinting of some sort - or an equivalent), this evolutionary instinct is triggered in any environment where there is an abundance of light. However when they stop 'super squinting', they can see extremely well with very little light - I'm not closed to the idea of them seeing in pitch darkness but the idea is that they do need light to see, and they can distinguish colors as well as us (although possibly differently) etc...

Additional Information:
So I found this page, I'm not knowledgeable enough on the subject to be able to certify it but it seemed legit to me. As such, what I'd be interested is basically a humanoid life-form that while having terribly crappy photopic eyesight - they'd have very advanced/developed mesopic/scotopic eyesight, including the ability to distinguish colors well (even though that is in contradiction), all of which due to the brightness of the star their homeworld orbits, like previously stated.

(Let alone if it's possible)
How could a life form that is mostly blind in daylight see perfectly with very little light?

Let me know if more info is needed on the setting but I'm pretty open-minded. (Although I would prefer actual science than handwaving, I'm pretty good at that on my own :P )

  • $\begingroup$ There's an episode of the old Star Trek where Spock appears to have been blinded. It turns out that he has a nictitating membrane (en.wikipedia.org/wiki/Nictitating_membrane) that blocks extremely bright light, then eventually opens again. Come to think of it, I think Vulcans are supposed to have better night vision than humans. $\endgroup$ Oct 26, 2015 at 20:53
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    $\begingroup$ If you didn't have irises in your eyes to regulate light intake, this would be "normal" for you. Many sighted deep-sea creatures, if they could survive the pressure change, would be blind during daylight hours at the surface. $\endgroup$
    – KeithS
    Oct 26, 2015 at 22:12
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    $\begingroup$ Very bright stars burn fuel quickly and turn supernova in just few millions of years. And have strong radiation. Not a good settings for advanced life. Main sequence stars have better chance to have habitable planets. $\endgroup$ Oct 27, 2015 at 17:01
  • $\begingroup$ I suppose that's another problem in and of itself - however I think there might be a couple of other ways too envision where a species could evolve in an environment where there's often a "Brightness Overload" $\endgroup$ Oct 27, 2015 at 17:28

6 Answers 6


There are two types of cells in mammalian eyes - rods and cones.

Rods are long photoreceptor cells that are highly sensitive to light, and are of use primarily in night vision, yet we have only one type of rod cell (that is maximally sensitive to blue-green light), hence we can only see in shades of that colour, which we interpret as grey.

However, when rods are exposed to high levels of light, the photosensitive pigment is 'bleached' by the excessive light, and cannot return to its unbleached state to detect more light.

On the other hand, cone cells are much shorter and cone shaped (hence their name), and are far less sensitive to light, requiring much higher levels of light to bleach to the point of uselessness. Humans have three types of these, each type maximally sensitive to either red, green or blue. Humans also have a great number of these cells, and each type far outnumbers rod cells.

This means that humans eyesight is optimal during daylight. To invert this, simply swap rods for cones. In such a situation, the species in question would have their most sensitive colour vision operable at night, while during daylight, all those sensitive rods would be bleached out and inactive while the few, far less sensitive, cones remained functional.

Now, your alien probably will not have rod and cone cells, but they have to have something similar if they're going to be able to see at any time. Simply by evolving to have their best vision at night, they'll have their more sensitive cells being more numerous and diverse in their sensitivity ranges, while less sensitive cells will be less numerous and less diverse. This will achieve the stated goal of sensitive night vision and poor day vision.

  • $\begingroup$ I like this answer a lot!! - And I guess this would bring about a bunch of xenobiology questions on what different type of colors etc... could a species with more than 3 type of rods or cones could see (or 'different' types). !! Thanks! $\endgroup$ Oct 27, 2015 at 1:42
  • $\begingroup$ «Humans also have a great number of these cells, and each type far outnumbers cone cells.» Are “these” the cone cells? Did you mean «...each type far outnumbers rod cells»? Great answer, though! $\endgroup$
    – DaG
    Oct 27, 2015 at 11:59
  • $\begingroup$ @DaG, Thanks. I've corrected that. $\endgroup$
    – Monty Wild
    Oct 27, 2015 at 23:29
  • $\begingroup$ +1 Great addition of details to the sensory saturation part of my answer. $\endgroup$
    – Samuel
    Oct 28, 2015 at 20:04

It's entirely possible.

Have you ever had your eyes dilated at the doctor's office? It makes your pupils very large because the muscles to contract them are temporarily paralyzed. If you go outside without some pretty dark sunglasses you can't open your eyes because it's so painful due to being far too bright, however, seeing in low light is no problem.

If this form of life has very sensitive eyes, like those very good for low light vision, then it's entirely plausible that they can't see well in daylight. If they have large pupils and no mechanism to contract them sufficiently then they will maintain eyes too sensative to work in full daylight.

You may also look into the concept of sensory saturation. If light levels above a certain threshold saturate the optical receptor cells of this life form then while they may not experience pain from full daylight, they won't be able to physically see anything in it. Their vision would be whited out.

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    $\begingroup$ To add to this (since the OP mentions "super-squinting"), their eyes could have developed underground to be extra sensitive/have large pupils, and due to a local maxima (svpow.com/2012/09/30/…) they could not develop any better when they ventured out into the light. Instead they evolved a new body part to compensate by filtering out/blocking most of the bright light to let them have minimally-viable vision during daytime to avoid predators or gather food, ie, "super-squinting". $\endgroup$
    – thanby
    Oct 27, 2015 at 8:29
  • $\begingroup$ Great answer. I had to walk three miles home from a hospital once on a bright sunny day after having my eyes dilated. Got some very funny looks and people crossing the street to avoid me as I stumbled along with my eyes screwed up... $\endgroup$ Oct 27, 2015 at 11:32
  • $\begingroup$ I find thanby's comment completes this answer pretty well - I was having a hard time figuring out how that would fit with a super bright star nearby - but then the locale/explanation wasn't itself part of the question (to avoid it being too vague) $\endgroup$ Oct 27, 2015 at 14:26
  • $\begingroup$ @Spacemonkey If you consider that the life forms only go outside at night it makes sense they wouldn't evolve particularly good daytime vision. For instance, humans have relatively bad night vision, because we're evolved to go out in the day. If the difference in brightness between night and day were even larger, it's unlikely the range of our vision for different light conditions would increase, so we'd be even worse off at night. Or vice versa for the night-time creatures. $\endgroup$
    – Samuel
    Oct 27, 2015 at 16:43
  • $\begingroup$ I entirely agree - the idea however was that the brigthness of the star was too much for proper day vision to develop - making the species develop the great eyesight when it 'can' see, which is during night time or in areas where the light isn't as intense. I guess it would make more sense for them to develop eyesight that CAN deal with the surplus light from an evolutionary standpoint - but the question was mostly if it was possible and not that much the 'what' or 'how' - I'm hesitant to create a new question just on this as it would be very similar $\endgroup$ Oct 27, 2015 at 17:25

This is in fact a reality for a number of people.

During a recent documentary for the BBC, detailing the stages of pregnancy and the differences our genes can make in our lives, they looked at an island where a lot of the inhabitants had a form of colour blindness.

This meant that they found it very difficult to see during the day.

However at night, their vision was incredible.

Here's a clip from the show.


I read somewhere that cats see better at night than in the day because during the day, their pupils are a slit, but at night they are round. Your race of nightseers might have really big round eyes.

I think the seeing color at night part of the question is actually a separate question. For humans blue things look blue because blue objects reflect mostly blue light and absorb the rest. You will note that light is needed to see the colors. Many divers prefer night dives because during the day most colors are filtered out in the first few feet of water. Bringing a light source at night can make the colors of the fish really pop. But perhaps if just a little bit of light is enough to see really, really well, it's enough to see color as well.

This resource might help:



If you've ever slept in total darkness and suddenly turned the lights on after waking up, you'd know how painful an experience it can be to wait while your eyes adapt to the light. Not only do your eyes hurt while they adapt, you also don't see very well at all.

The effect is similar to when you look directly into the sun; your eyes simply cannot deal with all that light. In order to avoid getting their photosensitive sensors burned off, your eyes will try to limit the amount of light that enter. Conversely, in order to see better at night, they will try to let in as much light in as they can.

To see well in the dark, but not so well in the light, we only need eyes that are particularly sensitive to light and does not adapt very well to changes in brightness; so basically, as long as their eyes cannot adapt to a brighter environment, your creatures will be essentially blind in it.

Now that we know how a creature can see well in the dark and not so well in the light, we only need to ask ourselves how they'd evolve. The answer is simple: You just need to toss them into an environment in which night vision is essential for survival, while light vision is only marginally useful if at all.

A dense forest in which it is almost always very dark for instance, would be a perfect place for your civilization to evolve. Of course, as soon as they need to leave the darkness — for example in order to trade — they'll have to adapt to a brighter future.

  • $\begingroup$ Hmm, it's kind of the conundrum I'm trying to avoid. If it's as simple as the eye adapting to the ambiant light then I'm assuming it would be fairly quick for the species to evolve to deal with the light. $\endgroup$ Oct 26, 2015 at 21:42
  • $\begingroup$ Not necessarily. If your civilization has had little to no contact to broad daylight over, say, millions of years, they probably won't be able to adapt to daylight that fast. At best, there might be 1 out of millions or billions who could somewhat see in the light. But I see your problem; if your civilization survived for so long without daylight, it wouldn't make much sense if the situation changed so suddenly. $\endgroup$
    – Nolonar
    Oct 26, 2015 at 22:05
  • $\begingroup$ These things happen on evolutionary timescales - the human eye is quite well adapted to the normal range on earth, but even then we have people who wear sunglasses a lot. $\endgroup$
    – Sobrique
    Oct 27, 2015 at 13:42

Many animals have better vision in night than in daylight. Elephants, who are of nearly human intelligence, see better in the night than in the day. So that is very close to an example of an intelligent alien life form who sees better in dim night light than in the bright daylight.


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