Man's physical universe

xanabras

UNIT VI

SECTION 2

LIGHT MAY BE PRODUCED BY LUMINESCENCE

Many substances radiate light when heated to a high temperature;

this process is called incandescence. It is not necessary, however, to

heat objects in order to cause them to emit light.

energy are used to produce cold light,

Various types of

the process being called luminescence.

Several forms of luminescence are still laboratory curiosities;

but other forms, such as electroluminescence, fluorescence, and phosphorescence,

discussed in this Section, have graduated from the laboratory

during the past twenty years and are being employed in many

useful applications, even to the extent of revolutionizing such industries

as electrical advertising and Mazda-lamp manufacture.

Luminescence or Cold Light May Be Produced by Various Forms of

Energy.

Bioluminescence is well illustrated by the firefly.

Fireflies have long

excited the curiosity of man. The firefly's light is produced by the

oxidation of a protein-like substance, luciferin, in the presence of

moisture and the catalyst, luciferase, an enzyme. Some people have

thought that the mastery of the secret of the firefly would yield the

most efUcient light because the light of the firefly is cold, but actually

the firefly is less efUcient than any common type of lighting equipment,

considering the amount of oxygen required to produce a given amount

of light. The flashes of light by the firefly are produced by forcing air

to the luminous cells. Glowworms are the larvae of fireflies.

Besides fireflies, bioluminescence is produced by certain kinds of

beetles, by bacteria that cause meat or dead fish to glow, by noctiluca,

the one-celled animals in ocean water that glow when disturbed, by

deep-sea fish, and by thousands of species of mollusks, shellfish, centipedes,

jellyfish, marine worms, and earthworms.

Chemiluminescence may be produced by various chemical reactions

not associated with life. For example, photographic pyrogallol will

give an orange-red luminescence when treated with formaldehyde and

hydrogen peroxide in a strongly alkaline solution. Luminol, 3-aminophthalhydrazide,

gives a brilliant blue light when oxidized.

398

Citric acid,

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