Light or Night

Among our four senses the one that we trust the most and that is perhaps used the most is vision. Vision is a wonderful gift that we have. But how does this vision work. Obviously we all know we are able to see because of our eyes. Thus we have vision because of our eyes. But that’s not the whole fact. We can see things around us not only because of our eyes but also for light. I would say that light is more important for the vision as compared to the eyes.

Now how does this vision work? Or simply I can ask that, how do we see things? Well, to understand this we need to understand the nature of light itself. Light is an electromagnetic radiation. Visible light is a section of the whole electromagnetic spectrum. It has the wavelength from 400 nm to 700 nm. In short we can say that the section of the electromagnetic spectrum whose wavelength ranges from 400 nm – 700 nm is the visible light. But if subdivide the visible light into more sections in terms of the wavelength, we get more seven sections. These seven sections are what we call as colors. These colors are called VIBGYOR (violet, indigo, blue, green, yellow, orange, and red). Red has the longest wavelength while violet has the least. Combination of two or more of these colors make the other colors and the combination of the colors make the white color. That is why the light having all these colors is called white light. 

Now we come to the question that how do we see things. When light falls on an object, an object will absorb some colors and reflect the remaining colors. Consider white light falling on an object, we suppose that the object absorbs all the colors in VIBGYOR except blue and it reflects only blue color then we see the object to be blue in color. That means we are seeing the blue light. When an object absorbs all the color in the white light then the object will be black in color because it will reflect no color. And when an object reflect all the colors in the white light, then it the object will be white. So when we see any object to be white it means we are seeing light consisting of all the colors. This is how we see everything around us. In the night that is why we are not able to see anything because no light is there. So our vision is like this, light or no light.

But what determines that what will be absorbed and what will be not? This is an important question. The answer to this question led to the development of an entirely new branch of science called spectroscopy. Every atom absorbs light in a unique pattern. Let us see how this works. When atom light falls in atom (on an object and object is made up of atoms), the electron on the outermost shell gains energy and goes to the lower shell temporarily. Almost instantaneously, the electron again goes to the outer shell by losing energy in form of light. Now the light that it emits consist the colors in it in a definite pattern. It is called emission spectra of an atom and the pattern for absorption is called absorption spectra. Emission spectrum is the photographic negative of the absorption spectrum. For each atom the emission spectrum or the absorption spectrum is unique. It can be told as the fingerprint of an atom.

Thus we can identify an atom if we know the emission spectrum. This is how astronomers know what is the composition of the celestial bodies in the outer space like sun, planets etc. Light is an important part for astronomy and astrophysics.

In my next article I will be sharing more wonderful things about light. Why is it so amazing? I will also mention many more important characteristics of light.