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Are black/gray/white considered as colors and their properties

  1. Nov 28, 2008 #1
    Hello. I am in a black hole here.

    I've did a bit of research on my own on colors and here's what i've found, briefly.

    Objects reflect and absorb different wavelengths and that determines their color. So, an apple is red, because it reflects more red from the spectrum and absorbs more wavelengths right and left from the red ranges. Then, gray objects reflect all wavelengths of light equally. White objects are simply lighter gray objects and also reflect all wavelengths of light equally but more of it. Black objects are darker grays who also are neutral and reflect all wavelengths equally, but in lesser amounts, where very dark objects appear black to us, but in reality they still reflect tiny amounts of light which we can't perceive, but it's still equal in all wavelengths. So to some it up, when talking in physics language, gray (and its extremes in white and black) are NOT to be considered colors.

    Where in the arts world, where black and white and the inbetweens used additively to affect the other colors, are considered colors equal to the rest of the spectrum?

    I seek the truth and explanations. Thanks.
     
  2. jcsd
  3. Nov 28, 2008 #2

    Danger

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    Welcome to PF, Hr1100.
    I was involved in the screen printing business for a fair while, and I still get confused about this. We had quite a lengthy discussion on the subject here on PF a couple of years ago. If my memory serves, black is definitely a pigment but not a true colour. Different disciplines seem to have different standards, though.
     
  4. Nov 29, 2008 #3
    THanks for the reply, but what about the pure physics side of it? Is it really they way i have understand it or i am wrong?
     
  5. Nov 29, 2008 #4

    Danger

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    That's up for someone more knowledgeable than me to answer. As far as I know, white is all colours, and black is none by normal standards.
     
  6. Nov 29, 2008 #5
    Black grey and white are not *technically* colours. Human perception of the colour black is due to no (or a relatively very low number of) photons reaching the eye from an area of material.

    White is not technically a colour - it is actually a composition of photons with wavelengths equally distributed across the visible spectrum. Think back to your first physics lessons about light - when you mix the three primary colours of light (blue, green and red) together you get white. This works because red, green and blue are roughly equally spaced across the spectrum and the simple light filters used on coloured bulbs and torches allow quite a large range of light wavelengths through per colour (e.g. a green one would probably filter out everything outside the range 495–570 nm). When you use all three coloured lights you actually are combining about 90% of the spectrum together as you're only really missing small bits of the spectrum between red, green and blue - thus you get white.

    For a colour to be a true physical colour, it must have a wavelength. A photon with a wavelength of 550 nanometers would be green.

    The intensity of any colour is the number of photons released from a set sized area of material per second. Here's a comparison of dark red and bright red:

    Dark:
    Photon wavelength = 700nm
    Photon energy (E=hf) = 2.915×10^-19
    Number of photons per second emitted per square meter: (Relatively) few

    Bright:
    Photon wavelength = 700nm
    Photon energy (E=hf) = 2.915×10^-19
    Number of photons per second emitted per square meter: Lots!

    So white is a high number of photons of an equal amount of all visible wavelengths, emitted from a set area of material. Grey is simply a lower emission rate. Black is a very low emission rate.

    This also explains why lasers are able to cut through metal. A laser is basically an extremely high intensity beam of red light. The reason it is high intensity is that a laser emits a very high number of photons in a very fine beam. As each photon is absorbed into the metal, it is dissipated as heat. The more photons per second that are absorbed by the metal, the more heat you get. Once you concentrate enough photons into a small area and have trillions upon trillions upon trillions hitting the metal per second, you can generate enough heat to melt that area of metal, therefore cutting through it.

    Another interesting example is space. Human perception of space is mainly black because from most directions there are not enough photons reaching earth for your eye to register any brightness. When you see a star, you're looking at a whole spectrum of colours emitted together and therefore you see a little white dot.
     
    Last edited: Nov 29, 2008
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