See. Verb. To See: to use our sense of sight, to see direct or reflected light with our eyes.
Also: To understand: I see what you mean; I could see how that would work.
Visually, sight is totally dependent upon light; we cannot see anything that light is not emitted from or reflected from or transmitted through (without absorption).
All light we can see is contained within a very narrow band of wavelengths of something called the Electro-magnetic spectrum. Typically we see light with wavelengths between 0.4 and 0.7 of a millionth of a metre, that is, with frequencies between 6 – 9 x 100,000,000,000,000 cycles per second (6-9 x 10ˆ14 cps) The wavelength is given as the speed of light (c) divided by the frequency of the light : wl = c/f. Although there are virtually an unlimited number of different wavelengths, and therefore colours in this range, most humans can only distinguish around 10 million different colours.
(By Marc Mongenet (Own work) [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)%5D, via Wikimedia Commons)
Most people find it hard to accept that the two colours they see and use most often in their lives are not actually colours as such – there is no single wavelength of light which represents either Black or White!
How can that be?
Well, for the other 9million, 999 thousand, 998 colours our eyes are able to fine tune in to one very small part of the visible light spectrum of colours (let’s call it the rainbow for short) and we can just about tell it apart from it’s two nearest neighbours and all the other colours but with black we don’t see one wavelength – we see NO wavelengths at all! Black is simply the name we ascribe to what we see when we don’t see light coming from the spot where we ‘see’ black. Black is the total (or near total) absence of light.
White light is exactly the opposite, rather than no colour, white is what we see when we see ALL colours simultaneously and at the same level of intensity. Our brain and eyes can cheat a little here and can see white even when some of the 10 million colours are missing, providing that there is a wide enough range of the rainbow colours for us to mix together to come up with ‘pure’ white.
If we use what are known as the 3 primary colours (Red, Green and Blue for example (in Fig 1) in equal measure the combination can give ‘white’ light. We can see this very simply for ourselves with a prism of clear glass or plastic. Shining a beam of sunlight through a slit (like from a pair of partly drawn curtains or blinds) onto the prism will split the ‘white’ light into a rainbow spectrum within which we can easily distinguish seven major colour groups (red, orange, yellow, green, blue, indigo and violet. roy.g.biv) but in reality contain many more different shades of colour. (The bluer light is more bent by the prism than the red).
Curiously, and again contrary to what might seem common sense, there is no such colour as grey either! All shades of grey are simply varying intensity levels of the all or nothing, white or black light situation. (You won’t find a grey in a rainbow!)
So to conclude roughly as i started: I can see everything (all at once, equally) when i see white and can see nothing at all when i see black.