The range of visible light is not sharply defined, either. Human eyes have three types of light sensitive cells— red, green, and blue cone cells— which respond to broad, overlapping ranges of wavelengths. Red and green largely overlap; red light looks different from green light only because the red cone cells respond to it slightly more than the green cone cells (a stronger signal is sent to the brain, and the brain sorts it out). Individual humans have different response curves, too. Some people’s red and green sensitivities overlap so completely that they are red-green colorblind. (http://www.coffeeshopphysics.com/articles/2013-02/01_viruses_have_no_color/)
Sunlight has the full spectrum of color “wavelengths” within the “visible” part of the electromagnetic spectrum. Because sunlight has a wide color spectrum, it renders the colors of an object or artwork accurately. Visually, colors look more natural to us when illuminated with sunlight. Skin tones tend to look better in sunlight… Cameras have an easier time rendering colors more accurately in sunlight than from an artificial light source. (http://bernardkatz.com/how-to-light-art-glass-lighting-guide/)
Artificial light sources can have narrow color spectrums with wave peaks higher in certain parts of their spectrums. Compact fluorescents (CFL) have narrow very peaky waves in their color spectrums. This is part of the reason why the light from fluorescents can be very unpleasing. Skin tones and artwork can look bad in this kind of light. (http://bernardkatz.com/how-to-light-art-glass-lighting-guide/)
Above is a diagram of how a rainbow appears in the sky. Firstly the sunlight shines into a rain drop and refracts. Then it refracts to another side and disperses the spectrum from red to violet. This creates a rainbow. NB: You are not able to see a rainbow unless the light shining from the sun is behind your eye. (http://wordpress.as.edu.au/jbourke/2013/03/13/dispersion/)
Newton was the first one to investigate the way a glass prism “disperses” a beam of light into a spectrum. He then went beyond that, and used a second prism to recombine the dispersed light into a white-light beam. In doing so, he showed that white light was a mixture of colors, and started a whole different branch of optics that might be called “color science,” but is more properly called “spectroscopy.”
In most kinds of glass, the speed of light is faster at longer wavelengths, so blue light has the greatest angle of deviation and red light the smallest. That’s the way it’s shown in this figure. However, it’s possible in some kinds of glass to reverse this ordering of the spectrum. It’s always either ROY G. BIV or BIV G. YOR, though.
No matter how big the raindrop, the path of colored rays through it go like this, making the same angles with the original white ray. The angles are determined by the index of refraction of the water for light of different colors. Obviously, red light has the biggest speed (smallest n) and violet light the smallest speed, inside the water.
The refraction inside the water drop determines the angles that the colored rays emerge, and thereby the angles between the color in the rainbow and the “antisun” at its center.
(banyak hal menarik lainnya yang belum di copas disini TT)