Sunday, September 4, 2011

Why don’t we see black light?

Q) Why don’t we see black light?
I had asked this question to my teacher and she had told me that black was the mere absence of light and not a light by itself. I appreciate all the effort the teacher had put into answering this question for me. 

I have seen a villain in Justice League, use black torch to engulf the heroes into a realm of eternal darkness, now don't tell me that he does it with the absence of light!!!! I demand  anexplanation!

Don’t we see crows in bright daylight? 

Seriously, I did not fall for this answer. I used to wonder if there can be red light, blue light, green light, then we might as well have a black light. Time after time, my teachers had given me the same answer and finally one day I got a reasonable answer.

If you have seen how a projector projects characters on the screen, you will notice that even though the screen itself is white, the projector can project all kinds of light combinations. Yes it can project black on a white screen. This was a major revelation to me.

Black light bulbs don’t exist because you don’t need to darken a place using a bulb, you are comfortable with reducing the light intensity and living in shadow, but like in a projector it is possible to project black onto a region. Or an entire room for that matter. Yeah, well think again!!! 

There are black light parties celebrated in various parts of the world, and we can see them in movies. Here's what, today we do have black lights. Its going on now and we are not aware of it ( go on, google black lights)

I am aware that black ink is made by saturating red or blue ink till it appears black. As per physics white light is combination of all colours and black is absence of all the colours. But look at my line of questioning. It is very evident that man can see only a very small part of the colour spectrum. If something is black to you, can you justify that it is black to a cow, or a dog, or an eagle, an elephant. No!! You can’t because they see colours in different spectrum. 

This subject is prone to discussions from a lot of considerations and I welcome you to comment against the discussion or in support of it. But seriously, look at the Electromagnetic spectrum, and look at what we call colours. Isn’t it justifiable to expect more from your teacher than all of that you can find in a text book or encyclopaedia for that matter?

I recently came across an article on how black lights work, interested readers are free to visit this site. 


  1. ohh thats really great ! Really didnt know that something like black light existed. Good, learnt something new.

  2. When you see blackness, the material that appears black is absorbing most of the light shining on it. when you look at something green, the light shining on it is absorbed, and the light that is reflected by the object is green. the color you see is the wavelength of light that is not absorbed by the object, and is reflected back into your retina. A black light that makes things glow is a different form of light. it has a shorter wavelength, and when a material called a phosphor is hit by this form of radiation, the phosphorescent material is irradiated and emits its own light in the form of photons.

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