Revision:Visual Light

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Wavelength: 3.5 × 10^-7m to 7.5 × 10^-7m

Sources

Very hot bodies (progressively red-hot, yellow-hot and then white-hot), discharge lamps (eg, most bulbs), phosphorescence and fluorescence of other types of electromagnetic radiation into visible light.

Detection

Photographic plates, photocells, the human eye.

Uses

Cathode ray tubes, which emit light, are used for televisions, computer monitors and the like. LED displays are used for cheap low resolution visual information. LCDs use the reflection of light for a similar goal. Bulbs are used for lighting which human beings and other animals then use as an aid for (amongst other things) location resolving, navigation, communication, and peripheral/accessory movement (eg, lifting cups of tea).

Apart from all the everyday types of visual communication there are a few other less obvious uses for visible light (which do not depend on it's visible to humans property). One is for high-speed fibre optic links, where red light lasers, green light lasers and (in the future) blue light lasers can carry digital data across long distances at very high speed. With the emergence of the internet these high-bandwidth solutions hold the key to global information sharing since the current infrastructure is not be capable of sustaining the emerging traffic.

Notes

The label "Visible" light demonstrates the ego-centricity of the human race. The short side of infrared and the long side of ultraviolet are separated by an extremely short band (relatively speaking) of radiation which is detectable by the human eye. It is unlikely that another race of intelligent beings, if it had a different natively "visible" section, would highlight the small part between the infrared and ultraviolet as being important.

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