Why you can not see the colours of light with your naked eyes?

Answer 1

Visible light is defined from wavelengths around 380nm to 780nm. Wavelengths smaller than 380nm are called ultraviolet and wavelengths larger than 780nm are called infrared. Based on those two names, you can probably guess how the visible spectrum is broken up.

Specifically (in nanometers):

Violet is 380-45

Blue is 450-495

green is 495-570

yellow is 570-590

orange is 590-620

red is 620-780

What is special about these wavelengths is that our eyes are optimized for them. We have what are called cones and rods inside our eyes (about 6 to 7 million cones and 75 to 100 million rods in each eye). These cones and rods are mini sensors, taking in the photons. Depending on the photon, they will affect different cones and different rods.

The cones can be broken up further into blue, green and red. The cones are responsible for everything we see as color. The blue cones pick up wavelengths from 380-500, but they are most sensitive around 430nm. The green cones are even more sensitive than blue ones; they pick up wavelengths from 450 to 630nm. This cone is most sensitive around 540nm. The final cone, the red cone, goes from 500nm to 700nm, peaking at around 580nm.

This may seem like a lot of data, but what it is telling us is that we don't have any cones for wavelengths outside of these ranges. So we defined the the wavelengths of the EM spectrum as visible light only because we can see those wavelengths.

Birds on the other hand, have four cones, the fourth being optimized for ultraviolet light. This kind of brings into question, what does blue/green/red even mean? That is a difficult question to answer because there is no inherent 'blueness' to light, its just how our brain interprets the signals for blue/green/red. We wouldn't know how to describe what birds see at all, because what they see has never been seen by people before.

That isn't to say we cant utilize the other spectrums. We use x-rays and infrared light all the time. What happens though, say in infrared goggles, is that we make sensors that CAN see those wavelengths, and then we manipulate that incoming wavelength into a wavelength that we can see. So if you have ever seen night vision before, its not that the night looks green, its just a conventional way to show you what you cant possibly see.

Answer 2

We humans can respond to a limited part of the electromagnetic spectrum - this we call visible light. We have three sets of cones to detect colours, and their spectral response overlaps, thus we see a continuum of light.

Birds, butterflies and bees have extended colour vision, and some have several more colour sensors than us. For this is more important to them. [is the fruit ripe or poisonous.]

By and large herbivores and omnivores, and carnivores have no colour vision, for they don't need it.

Answer 3

Short answer:

We don't see them because we can't see them. If we could see them then we would be able to see them and the question is irrelevant.

More detailed answer:

Because seeing is the definition of a process by which a certain range of electromagnetic frequencies strike a portion of any organ called an eye, and set off chemical reactions which create signals along the nervous system; these are interpreted by the brain as sight or vision. The eyes of certain species are developed to detect light in this manner from a certain range; for instance, bees and Spiders can see into the UV range while some snakes can "see" into the infrared. Visible light to them may be invisible to us and vice versa, simply because they have (or have not) developed to see that frequency and we have (or have not) developed to see it as well.

If we could see any other frquency outside this range, then they would be visible as well and would be included in the term "visible light". Thus, we cannot see it simply because we cannot see it, and we can see it simply because we can see it. Those frequencies are not physically seen because they cannot set off a relavent reaction and signal in the eye, hence cannot be received by the brain.

Sound waves are mechanical waves, and so they cannot be seen by definition. Instead, they are heard: a physical process results in the signal being transferred to the brain and processed in a similar way to sight.

Answer 4

You can see the colors of light with your naked eye, but only after it has been refracted by an object which acts like a prism: rain drops, pieces of glass, soap bubbles, certain atmospheric phenomena, etc.

Answer 5

Because it's on the other side of the Earth, that being kind of the definition of "night."

Answer 6

The human eye lacks a tapetum lucidum