Explain how the eye adapts to light and dark?
466552
The muscles of the iris contract when it's bright so too much light doesn't get in, and dialates when it gets darker, to let more light in.
1119194
Science has shown that we look different based on where we live. Do you no get enough sun light you have pale skin. More sun the darker your skin based on how much vitamin D you need. If you have more sun your eyes would he darker to. Less sun light the lighter your eyes so that you would let more light in for better sight. Also the eyes would form differently based on light. and wind. If the area was bright and or windy then the eyes would not open that much and there fore they are what we now call slanted. \n\nThese are just a  few of our differences and why.
451298
We have two types of receptors (light-sensitive nerve cells) in the retina of the eye.  The two types are called 'rods' and 'cones.'  The 'rods' (so-called because of their shape) respond to low-levels of light and are useful for night vision.  However, since all rods are pretty much identical, they do not distinguish between colors ... our dim-light rod vision is "black and white."\n\nThere are three types of cones (again, so called becaues of their shape).  One responds to long-wavelengths of light, what we call the "reds".  One responds to medium-wavelengths, what we call "greens".  And the third responds to short-wavelengths (the highest energy), what we call the "blues" (unless you live in Mississippi, then the "blues" is something different :-) ).  \n\nThese ranges of wavelengths for the three types of cones are not exclusive ... they overlap.  In other words, the long-wavelength cones also respond to medium wavelengths, although to a lesser extent.  Because they overlap, every object that gives off different mixtures of wavelengths affect the different cones by different amounts.  This experience is what we call color.  (Unless you live in Britain.  They don't see in colors.  They see in colours.)
793828
We see things in different colours because light (usually white) reflects off surfaces and reach our eyes with a different frequency, for some is absorbed. When NO light reach our eyes, it simply appears as black. You can see this as some form of 'natural default' (i coined this term myself). \n\nTo help your understanding, think of seeing a piece of paper filled with different patches of colours and holes, placed in front of vaccuum space. The black that you see will be the holes where no light get bounced off. \n\nHope this helps=)
702227
You're right... the black absorbs light better, so you get less reflected glare in the eyes.
620358
Your photoreptors and your visual cortex cells randomly fire, it is background noise a bit like you get with a CCD camera. Also you may notice that if you put pressure on your eyeball (not too much!) you will see a bright spot - so photoreceptors respond to more that just light.\n\nI get this too and my vision is fine.
750439
amy is right.  this is the basis behind percieved perception.  what you see may be different than what somebody else sees however you speek of it as the same thing.\n\naarons answer is missing the part of transfering the light information into a chemical reaction inside the rod cells and then turn to electical activity.  this is where the possible problem occurs\nbetter yet heres the sequence \n\n1. Light rays enter the eyes by passing through the cornea, the aqueous, the pupil, the lens, the vitreous, and then striking the light sensitive nerve cells (rods and cones) in the retina.\n\n2. Visual processing begins in the retina. Light energy produces chemical changes in the retina's light sensitive cells. These cells, in turn, produce electrical activity.\n\n3. Nerve fibers from these cells join at the back of the eye to form the optic nerve.\n\n4. The optic nerve of each eye meets the other at the optic chiasm. Medial nerves of each optic nerve cross, but lateral nerves stay on the same side. The overlap of nerve fibers allows for depth perception.\n\n5. Electrical impulses are communicated to the visual cortex of the brain by way of the optic nerve.
938383
Actually, there's a good article in this month's National Geographic that touches on these sorts of questions.  It's called "From Fins to Wings.'"  The relevant text starts on page 121, and starts with Charles Darwin's own acknowledgment of the enormity of explaining a system as complex as the human eye as a result of random mutation and natural selection.\n\nThe discussion goes on to indicate (page 126) that over time, a greater certainty has evolved that photoreceptors in all species are "the handiwork of the same genes that build our own eyes".\n\nIt goes on to say, "Evolution then used these basic genes to fashion more sophisticated eyes, which eventually acquired a lens for turning light into an image."\n\nThere's also a neat series of drawings at the bottom of pages 126-127 that gives an intuitive feel for the discussion.\n\nThere's much more at the link.
848680
I have had that problem.  I asked my optometrist about it once.  They told me that it is normal.  It's a combination of a couple of factors:\n1.  Your eyes are trying to accomodate for the lack of light by adjusting to the dark.  This causes your pupils to dialate, which causes blood to flow more rapidly through your eyes, which over-stimulates the optic nerves.\n\n2.  Minor visual hallucination:  Your brain is trying to fill the void with images, trying to make sense of the newly-limited input filtering in.
477694
It's not true.\n\nMost animals don't have much in the way of eyes at all, of course, but you're probably more interested in vertebrates.\n\nMost vertebrates have very good color vision.  The primary exception is mammals.  (Snakes are also an exception, for similar reasons.)  We got a bit shafted because our ancestors in the Mesozoic (age of dinosaurs) were all nocturnal.  Nocturnal animals don't really need color vision (black & white works better in the dark), so our ancestors mostly lost it.  Then the dinosaurs died off and mammals retook the day and have been putting color vision back together ever since.\n\nMammalian color vision is, thus, not quite as good as that of the rest of the vertebrates.  Cats and dogs do have color vision, but not as good as ours, and ours isn't as good as that of most reptiles.
43367
Each of the eyes are slightly recessed, and each eye points in a slightly different direction.  This makes it so that depending on which eye detects the most light, the insect is able to determine the direction of the light.  Humans, by contrast, find the location of light by having a lens which focuses the incoming light on the photo-sensitive retina at the back of the eye.
76619
The answer lies in the structure of the eye.  There are two types of receptors in the eye, rods and cones.  Cones are the color receptors but are less sensitive to light.  Rods are very sensitive to light but do not distinguish color.\n\nMany animals, especially nocturnal animals, pack a greater number of rod receptors into their eyes allowing them greater sensitivity to light allowing them to see in conditions that are too dark for huuman eyes with their lesser number of rods.\n\nIt is a tradeoff between color and light sensitivity with humans weighing in more heavily in the color category.
328994
Dark does not push light away, the light is what is moving. Using your example of "over the horizon", the sun (which produces light) moves to the other side of the earth (where we can't see it) then we see dark. But dark does not move, it is just the term we have come up with for what it looks like when there is no light present.
931147
Amazing the natural selection process.  Originating form the times when we were living lifestyles more exposed to the weather, they help keep foreign materials from falling in our eyes.  Tree leaves, dust, rain, etc, coming from above us.\n\nTake a look at some of the earlier life forms, Neanderthals for example. see how thick their eye-brows, how deep their eye sockets are.
871539
Basically, Color, black and white are measured by the Cones and Rods in the back of you retinas.  And boy are there a lot of them.  But one eye might have a little more than the other eye  or there maybe more of them grouped in a certain location which may be the reason for the discreptancy.
524507
Simple answer:\n\nThe rods and cones in our eyes pick up on the different waves in light. The primary colors of light are:\nGreen\nRed\nBlue\nWith the combination of these different wavelengths of light we can get any of the other colors including yellow.\n\nPigments work different. Whereas the colors we recieve from  TV's and lightbulbs is by the combination or "addition" of wavelengths of light, pigmentation occurs by "subtraction" of light and it also has different primary colors. The primary colors of pigments (any object is seen by pigments whereas a TV's colors works by wavelenths of light rather than pigments) are:\nYellow\nBlue \nRed\nAnd those colors are seen by subtration meaning the light hits the particular object and every color gets absorbed except whatever color get reflected and that is the color we see.\n\nhope this helps.
890871
The eye detects wavelengths of electromagnetic radiation (fancy talk for light) that fall within the visible spectrum and are of sufficient luminosity to effectively stimulate the retina to send an interpretable message to the brain via the optic nerve.\n\nLuminous and non-luminous objects as you pose the question simply implies various levels of brightness and perhaps the 'source' of the light.  \n\nThe eye simply detects light and interprets the wavelengths.  If the object is the 'luminous source' of the light - as the sun, the eye's processing of the information is no different from the 'reflected' light from an object (perhaps what you mean by non-luminous) such as a tree or rock.\n\nThe physiology is the same.  \n\nThough - an intensely luminous object, or prolonged exposure to such, can damage the eye and even result in blindess.  (Don't look directly at the sun!!!).\n\nGood question and remember - KEEP STUDYING SCIENCE!!!