Hot answers tagged vision
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As mentioned in a number of other answers, there are three different color receptors in a typical person's eye. They respond to different wavelengths of light, as can be seen in the below diagram from wikimedia.
The $x$-axis is wavelength in nanometers, and the three curves represent the three receptors' response at those wavelengths. Any incoming light ...
43
The eye is sensitive to light with a wavelength in the range from about 700nm to 400nm, and for the non-colour blind all wavelengths in this range are detected by one or more of the cone cell types. So there are no hidden colours in this range.
Light outside the 700-400nm range can't be seen, so I suppose you could claim these are hidden colours, but then ...
15
It really depends on what you mean by colour.
If by colour you mean "the human brain's response to a given combination of wavelengths", then by definition there can be no invisible colours; wavelengths combinations that do not stimulate any cones in the eye are just equivalent to black.
If by colour you mean "a given combination of wavelengths", then we ...
14
The two effects are not related.
The size appearing larger is a matter of some speculation to this day, but it is purely a psychological effect. If you want to prove this, take a look a the moon while standing up and looking between your legs. It won't look nearly as large.
The red/orange color is related to the sunset being red. In fact, it's the same ...
13
(Source, Wikipedia Commons)
The moon is generally called a "Harvest Moon" when it appears that way (i.e. large and red) in autumn, amongst a few other names. There are other names that are associated with specific timeframes as well. The colour is due to atmospheric scattering (Also known as Rayleigh scattering):
may have noticed that they always ...
12
Your eye has three types of receptor cells, the sensitivity of each type peaking in different spectral regions. Roughly speaking, there's one that peaks in red, one blue, one green. (It's not quite so clear cut, but your brain is really good at sorting out messes like this!) When you look at a fire engine (assuming it's red) It's mostly the red receptors ...
12
You can't see clearly underwater for a couple of reasons. One is the thickness of your lens, but the main one is the index of refraction of your cornea.
For reference, here's the Wikipedia picture of a human eye.
According to Wikipedia, two-thirds of the refractive power of your eye is in your cornea, and the cornea's refractive index is about 1.376. ...
10
We have color perception because we are trichromats. In our genes there is code for three slightly different light-sensitive molecules. The light-sensitive cells in the retina are called cones, and neighbouring cones each produce one of the different versions of the light-senstive molecule. So each of the three cone-types responds slightly differently to the ...
9
This happens because the spectral response for each red/green/blue pixel in cameras don't exactly match the spectral response of the receptors of your eyes. For example, check here and here, and compare them to the human eye (and read the whole wiki article for interesting details on human color perception).
What digital cameras do, is to try to mimic your ...
8
Human color vision is based on four types of receptors in the retina: rods, and three types of cones. Their response to different wavelengths is shown in this graph:
.
It shows clearly how certain wavelenghts, mostly around the yellow-green portion of the spectrum, are absorbed more strongly, and by more types of cells, than the rest.
So it is normal ...
7
Am I right ?
Yes.
If so, what lenses should one wear in order to see clearly while under water ?
You don't need extra lens you have one in your eyes, just use goggles that makes a layer of air between the water and your eyes.
If you decide to put a convergent lens in front of your eyes it won't work because your eye will still not be able to ...
7
When you mix colors using Watercolors, then they mix as "Subtractive Colors". However, Light itself mixes as "Additive Colors".
Even though it might seem strange why the inherently same thing works so differently, it makes sense if you think about Watercolors, etc. as absorbing everything but that specific color.
7
The overlap that you might see in a diffraction grating doesn't occur in a rainbow, because rainbow are formed by refraction of light, not diffraction. The raindrops work like prisms, not diffraction gratings: it's a simple bending of the light by a frequency-dependent angle. There are no multiple orders of maxima to overlap.
For what it's worth, though, a ...
7
Quickly, try this: Imagine blindingly bright red light! Now blue! Now yellow!
You could see stark differences as you shifted from color to color, couldn't you?
Yet if you think about what just went on inside of your head, it didn't involve any color photons going into your eyes, did it? So, what you just did must be separate from the light frequencies ...
6
The human vision has 3 types of cones. (that is why all perception-based color spaces are 3 dimensional: LAB, XYZ, HSV ). Each cone type has a different sensitivity curve in the color spectrum (think of them as color filters). It gets complicated because these curves overlap: there isn't a single wavelength of light that triggers just one cone type.
So, in ...
6
There's certainly no problem being out in the Sun during an eclipse: There's nothing being emitted then that's not being emitted at other times. The danger is just that the relative darkness near totality may make it seem safe to look at the Sun, even when it's not. But as long as you don't look directly at the Sun, you're fine.
During the time when an ...
6
Not all colors are monochromatic (pure). The spectrum of colors is really only a spectrum of monochromatic colors, and that's why you can represent it on a line.
For non-monchromatic colors, you'd represent them with a gamut instead of a spectrum:
Here you'll see pink at x=0.45,y=0.3. The monochromatic colors are along the edge, i.e. the edge is the ...
6
The reason that colors combine as they do has everything to do with the response curves of the light-sensitive proteins in your eye. A response curve is just a function that tells you how strongly a particular protein reacts to a fixed amount of light a given frequency (or energy). There are three kinds of these photosensitive proteins (photopsins) in our ...
5
What @Michael said, plus your retina has sensors for roughly red, roughly green, and roughly blue, and not for any other colors.
(BTW, the green sensors are more sensitive, so it takes less green to make the same brightness.)
When you see something yellow, it's in between red and green, so it excites both of them, and your visual cortex happens to call that ...
5
The Wikipedia article Aberrations of the eye discusses this. The article is really about non-normal aberration i.e. the sort of thing that makes us have to wear spectacles, but it also mentions the aberrations in normal eyes. The conclusion is that normal eyes are actually pretty good with just a small amount of spherical aberration. The lens and cornea form ...
5
Yes it is possible
If the object has the same refractive index as a surrounding fluid it is not visible.
If the object does not produce or reflect light (such as a black hole) it is invisble.
complex systems are being produced to create nanoscale invisible objects now.
http://www.sciencedaily.com/releases/2012/05/120521104637.htm
5
I believe you should have googled first:
google hits
Especially the second link very clearly explains the main reason:
The primary reason why the color red is used for danger signals is that red light is scattered the least by air molecules. The effect of scattering is inversely related to the fourth power of the wavelength of a color. Therefore blue ...
4
I tracked down a spectrum of the sky at an altitude somewhere below 51° and overlaid it on the colors of the spectrum:
From this diagram, it appears that the intensity of the light admitted through the atmosphere diminishes significantly before reaching violet. Unless the perceiving retina was overpoweringly tuned to ...
4
The blackbody spectrum of the sun is the following, given $T=5778 K$. I admit I'm just copying from Wikipedia.
$$I(\nu,T) =\frac{ 2 h\nu^{3}}{c^2}\frac{1}{ e^{\frac{h\nu}{kT}}-1}$$
The comic suggests that the reflection from scattering transforms the above spectrum by $1/\lambda^4$ (as in, it is multiplied by this). Light is a wave, so $\nu \lambda=c$. ...
4
Color is basically formed in the brain not the eyes. Also the human eye can handle electromagnetic waves from 4000 to 7000 Angstrom, roughly, so called visible light. Above this range, the infrared region is found. It is not red in color or something, it is a name convention. Our eye can not handle it and so the brain dose not recognize it.
It is ...
4
Yes, It's true...
We know that our eyes have three types of cone cells - S (short), M (medium) & L (large). The naming is done in order to differentiate the cells from "which cell absorbs which color". S to Blue, M to Green and L to red. The peak wavelength of L is 564 nm, yellowish-green. The peak of M is 534 nm, bluish-green. The peak of S is 420 nm, ...
4
This is more of a psychology question. After you start seeing things, you notice that a certain side of your vision is the part that will see your finger if you touch your forehead, and the other side will see your finger if you touch your lips. We designate the first as "up" and the second as "down".
The brain just gets a bunch of signals. "up" and "down" ...
3
The Wikipedia article on Martian Canals is very good.
The existence of canals in the "martian made" sense, instead of the natural sense, was primarily due to wishful thinking on the part of Percival Lowell. The original intention based on observations made in 1877 was probably natural channels. Quoting a snippet from the Wikipedia article:
The Italian ...
3
It is an optical illusion. It only looks bigger near the horizon because it can more easily be compared to familiar objects on the ground. If you hold up a coin in front of your line of sight while looking at the moon and then compare your arm extension for a low moon and a high moon you see that they are the same. IOW, the diameters are the same.
Don't ...
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