Man's physical universe

xanabras

LIGHT MAY BE PRODUCED BY LUMINESCENCE 399

cane sugar, starch, and many other similar materials show chemiluminescence

when fused and then oxidized.

An interesting application of chemiluminescence is a powder,

" Bloodglo," developed by Evans W. Cottman for use in criminology and

medicine. The powder is dissolved in water.

When the solution comes into contact with

the merest trace of blood, it glows in the

dark, the haemoglobin acting as the oxidizing

agent.

Electroluminescence is produced when

passed through vacuum tubes

electricity is

containing traces of gas. Neon tubes produce

light by electroluminescence. Brush

discharges such as St. Elmo's fire, which

r r u^ u- Fig. 173. A glass bowl

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appears as a tip ot light on ship masts or . •

j ^ i u l

r 11- . .

^s caused to glow by chemichurch

spires, are electroluminescence.

^ luminescence. (Courtesy of

Radioluminescence is produced by radio- Evans W. Cottman.)

active substances.

Crystalloliiminescence is the emission of light when certain substances

crystallize from solution.

Triboluminescence is the production of light by crushing certain

crystals.

Acousticoluminescence is the production of light by vibrating viscous

liquids such as glycerol at a high frequency.

Still another type of luminescence is produced by friction such as

appears when tire tape or adhesive tape is stripped from a roll or when

mercury is distilled under reduced pressure.

It is apparent that nearly every form of energy may be changed

directly into light energy. Most of the forms of luminescence are still

laboratory curiosities, although electroluminescence is widely used in

neon-type lights and in mercury- and sodium-vapor lamps. Still

another type of luminescence, phosphorescence and fluorescence,

described in this Section, is applied in modern fluorescent lighting.

one can tell just what great possibilities the remaining laboratory

curiosities may have in the service of mankind. Falling snowflakes,

waterspouts, and dust from volcanic eruptions sometimes luminesce.

The Aurora Borealis is another luminescent phenomenon. Very little

is known about the causes of these examples of natural luminescence.

Mercury-vapor Lamps Produce Light by Luminescence.

About 1900 Peter Cooper Hewitt developed the mercury-vapor lamp,

which is used in photographic studios because of its highly actinic

No

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