7 colors of RAINBOW
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The document discusses the number of colors in the visible light spectrum and rainbows. It states that the human eye can distinguish around 100 colors in a spectrum. Newton originally identified 7 main colors - red, orange, yellow, green, blue, indigo, and violet. However, the number of colors is an arbitrary distinction, as the spectrum is actually continuous. Rainbows contain less saturated colors than a spectrum due to the way light is refracted through water droplets. The number of distinguishable colors in a rainbow can vary depending on droplet size.
![Number of colours in spectrum or rainbow
A spectrum obtained using a glass prism and a point source is a continuum of wavelengths without
bands. The number of colours that the human eye is able to distinguish in a spectrum is in the order of
[6]
100. Accordingly, the Munsellcolour system (a 20th-century system for numerically describing colours,
based on equal steps for human visual perception) distinguishes 100 hues. The apparent discreteness of
main colours is an artefact of human perception and the exact number of main colours is a somewhat
arbitrary choice.
Red
Orange
Yellow
Green
Blue
Indigo
Violet
Newton originally (1672) divided the spectrum into five main colours; red, yellow, green, blue and violet.
Later he included orange and indigo, giving seven main colours by analogy to the number of notes in a
[1][7]
musical scale.
Rainbow (middle: real, bottom: computed) compared to true spectrum (top): unsaturated colours and different colour profile
The colour pattern of a rainbow is different from a spectrum, and the colours are less saturated. There is
spectral smearing in a rainbow owing to the fact that for any particular wavelength, there is a distribution
[8]
of exit angles, rather than a single unvarying angle. In addition, a rainbow is a blurred version of the bow
obtained from a point source, because the disk diameter of the sun (0.5°) cannot be neglected compared
to the width of a rainbow (2°). The number of colour bands of a rainbow may therefore be different from
the number of bands in a spectrum, especially if the droplets are either large or small. Therefore, the
number of colours of a rainbow is variable. If, however, the word rainbow is used inaccurately to
mean spectrum, it is the number of main colours in the spectrum.](https://image.slidesharecdn.com/numberofcoloursinspectrumorrainbow-131205160624-phpapp02/85/7-colors-of-RAINBOW-1-320.jpg)
7 colors of RAINBOW
- 1. Number of colours in spectrum or rainbow A spectrum obtained using a glass prism and a point source is a continuum of wavelengths without bands. The number of colours that the human eye is able to distinguish in a spectrum is in the order of [6] 100. Accordingly, the Munsellcolour system (a 20th-century system for numerically describing colours, based on equal steps for human visual perception) distinguishes 100 hues. The apparent discreteness of main colours is an artefact of human perception and the exact number of main colours is a somewhat arbitrary choice. Red Orange Yellow Green Blue Indigo Violet Newton originally (1672) divided the spectrum into five main colours; red, yellow, green, blue and violet. Later he included orange and indigo, giving seven main colours by analogy to the number of notes in a [1][7] musical scale. Rainbow (middle: real, bottom: computed) compared to true spectrum (top): unsaturated colours and different colour profile The colour pattern of a rainbow is different from a spectrum, and the colours are less saturated. There is spectral smearing in a rainbow owing to the fact that for any particular wavelength, there is a distribution [8] of exit angles, rather than a single unvarying angle. In addition, a rainbow is a blurred version of the bow obtained from a point source, because the disk diameter of the sun (0.5°) cannot be neglected compared to the width of a rainbow (2°). The number of colour bands of a rainbow may therefore be different from the number of bands in a spectrum, especially if the droplets are either large or small. Therefore, the number of colours of a rainbow is variable. If, however, the word rainbow is used inaccurately to mean spectrum, it is the number of main colours in the spectrum.