colour (physics)

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In physics, wavelength, or mixture of wavelengths, of light emitted or reflected from an object; in psychology, the subjective visual response to that combination of wavelengths. Visible white light consists of electromagnetic radiation of various wavelengths, and if a beam is refracted through a prism, it can be spread out into the visible spectrum (the part of the electromagnetic spectrum that can be detected by the human eye), in which the various colours correspond to different wavelengths. From long to short wavelengths (from about 700 to 400 nanometres) the colours are conventionally divided into red, orange, yellow, green, blue, indigo, and violet, though they merge smoothly into each other.

The colour of grass is green because grass absorbs some colours from the spectrum and those that it transmits or reflects are predominantly of wavelengths corresponding to green. A sheet of white paper reflects all the colours of the spectrum from its surface; black objects absorb all the colours of the spectrum.

Almost all colours can be visually matched by mixing proportions of red, green, and blue light. These are known as the additive primary colours. Different colour filters can also produce light of different colours. For example, a red filter transmits predominantly red light, the remaining colours of the spectrum being largely absorbed by the filter.

Mixing red, green, and blue light in the correct proportions produces white light. When these colours are mixed in different proportions, so-called secondary colours are formed; for example, blue + red = magenta, red + green = yellow, and green + blue = cyan. Yellow light is reflected from the surfaces of some flowers as the petals absorb blue light. Red and green light are reflected back, and these mix to give the sensation of yellow. However, yellow is also seen when monochromatic (single-wavelength) light of about 600 nanometres is reflected.

The wingless dragon holds jewels in its claws to represent prosperity. Saffron yellow symbolizes the power of the monarchy. Orange-red stands for Buddhism. Effective date: c. 1971. >>