PHOTOGRAPHY IN DARKNESS

Hawera Star, Volume LIII, 26 August 1933, Page 11

PHOTOGRAPHY IN DARKNESS

JN VISIBLE “ black lighit,” which pe;rmi'ts the t a hi. rig o.f photographs i!n the tlaTk, aids l dentists in teeth inspection,, increases egg production an'd weight of poultry, develops a red' colouring in certain, fruits, such as rosy cheeks on apples, guarantees good vision at nighit in the cockpit of an aeroplane, and provides the criminologist an infallible instrument to detect erasure and forgeries, was described by Mr Samuel G. Hibben, to the members of the Illuminating Engineering Society at a recent meeting in 'America.

“This invisible ‘blaek light/” said Mr Hibben, is pure ulitra-vioilet radiation, and is GO per cent free- of visible light. It is produced by two new' black bulb lamps, one consuming two amp'reS and the other ’five. They arc made of special cobalt glass. The bulbs of these lamps absorb 90 per Cent of visible light, and transmit SO to S 5 per cent, of the kind of ultra-violet wanted. The resultant radiations are relatively long in wave length—in the range of 3200 to 400 angstroms.

Uncanny Power of “Black Light

“Tliis long wave ultra-violet lends itself to pbo.to graphic and fluoiiescerut' effect's. The radiations are -rich in actinic value and- this makes it possible to take photographs in. complete darkness. Sucli a use has- already been suggested by means of automatic mec'hnmism for the purpose of photographing a thief or intruder unaware? At the present time one -lamp requires a time exposure of from five to seven seconds /to take a photograph in: the dark but by increasing the amount of ultfai-violet' a snapshot- .photograph i? permitted. Because they give off a luminous glow, or fluorescence, when radiated by invisible ultra-violet', imperfect teeth, false genus, spurious inks-, changes in pigments and paintings max' be detected. Also the age of some materials, such as marble and 1 statuary may be determined, and in criminology it is possible to match papers or fabrics or to discover forgeries an'd erasures. Fluorescence with ultra-violet is also useful in specialised advertising and for peculiar stage elf celts.”