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Proceedings of the American Academy of Arts and Sciences
VOL. XLVIII. No. 1.—MAY, 1912.
ON THE ULTRA VIOLET COMPONENT IN ARTIFICIAL
BY LOUIS BELL.
WITH TWO PLATES
INVESTIGATIONS ON LIGHT AND HEAT PUBLISHED WITH AID FROM THE
THE ULTRA VIOLET COMPONENT IN ARTIFICIAL LIGHT.
BY LOUIS BELL.
Presented March 13. Received March 25, 1912.
Purpose of the Investigation.
The fundamental purpose of this study has been definitely to evaluate the amount of energy given by various artificial illuminants in the ultra violet portion of the spectrum. In particular, beside determining the general proportion of ultra violet rays and their actual amount in each lamp investigated, the writer has determined. in absolute measure the ultra violet energy delivered by each light source for unit illuminating value. Assuming that each of the artificial lights studied is to be used to produce a certain given illumination, the amount of ultra violet radiation incidental to that illumination has been set down in absolute terms of ergs per second per sq. c. m. This classification of illuminants, which has not hitherto been made, is important in view of the possible harmful effects of radiation of short wave length which have been repeatedly discussed during the past few years. The amount of such possibly injurious radiation given by any particular lamp is a matter of small importance except as it is correlated with the illuminating power of the lamp, so that one may know to what amount of possibly harmful radiations he is exposed in securing a required degree of illumination.
Nature and extent of Radiations under Suspicion as harmful. — There has been much discussion concerning the effects of radiations of different wave lengths upon the eye. Without going extensively into an examination of the literature, which is very scattered and extensive, or of the physiological facts, some of which the writer now has under careful investigation and which will be reported later, it is sufficient here to say that the investigators of this matter may be divided into somewhat divergent schools. All agree that the extreme ultra violet rays, those of wave length less than 300 μu, which are absorbed by the cornea and so do not penetrate to the inner parts of the eye, produce when in sufficient intensity more or less serious damage to the corneal ephithelium, resulting in acute irritation, always accompanied by conjunctivitis, and sometimes by cloudiness of the cornea and other symptoms which go to make up the complex
injury which has come to be known as ophthalmia electrica. It is in effect a superficial sunburn of the eye and is often accompanied by a similar sunburn in the vicinity of the affected eye. Whether this 'particular sort of effect is produced also by ultra violet rays of slightly greater wave length, say up to 320 μμ oг 330 μμ, is a matter of some dispute, but most investigators have held this particular region under suspicion on account of the phenomena of snow blindness, which closely resemble those of the so-called ophthalmia electrica, and cannot be produced by the extreme ultra violet rays since the solar spectrum owing to atmospheric absorption is extremely weak at and below 300 μμ, very near to which point it is wholly cut off. It is, however, fairly rich at 320 to 330 μp, the cutting off by atmospheric absorption being rather sudden, as shown in a, Plate 1.
Now while the cornea cuts off only rays of wave length less than 300 μμ the lens of the human eye ordinarily absorbs the whole ultra violet, it being substantially due to this absorption that we are unable to see beyond the violet. This absorption extends to about wave length 380 μ and in old persons in whom the lens gets slightly yellow even as far as wave length 420 μμ. In early youth there is a very slight transmissibility of the lens in the region 315 to 330 μμ as shown by Hallauer. Now potentially the rays which are absorbed by a medium may produce changes in it and the ultra violet rays up to and including the extreme violet have been reputed by various writers to produce a large variety of lesions, including retinal injury due to the rays which may filter through the lens. The list of reputed dangers is a very long one including erythropsia, color scotomata, cataract and other serious results. The situation from the point of view of the ophthalmologists who seem to be really in fear of ultra violet radiations is well summed up by Schanz and Stockhausen. Other writers like Best 3 and Voege1 attach relatively little importance to the effect of the ultra violet as such and are inclined to attribute some of the phenomena to over-intense radiation of ordinary light or to causes not connected to radiation at all.
A third group, of which Birch-Hirschfeld 5 is a representative, holds an intermediate view. It should be noted that the permanent
1 Klin. Monatsbl. f. Augenheilk., Dec. 1909.
2Ztschr. f. Augenheilk., May 1910.
3 Klin. Monatsbl. f. Augenheilk., May 1909.
Die Ultravioletten Strahlen der modernen kuenstlichen Lichtquellen und ihre augenbliche Gefahr für das Auge. Berl., 1910.
5 Ztschr. f. Augenheilk., July 1908, and elsewhere.
injuries ascribed to ultra violet rays, like cataract and retinal degeneration, are charged to the radiations running even up to the visible spectrum, while the extreme ultra violet, absorbed by the cornea, produces only superficial lesions generally recovered in a few days.
From the standpoint of the present investigation it did not seem justifiable to attempt to pass without further investigation on the validity of any of the divergent views here noted, but to deal with the radiations of short wave length as a whole, including in the possibly injurious group all those radiations which have been under serious suspicion on clinical evidence by reputable investigators. The line has therefore been drawn between the ordinary lighting radiations and radiations of short wave length in the extreme violet and ultra violet of the spectrum, where the lighting value of the rays is negligible and their actinic value notably high.
Separation of the Ultra Violet from the Visible Spectrum. determined on such a separation of the radiations under grave suspicion of injurious action from the rest of the spectrum, it was next in order to find a suitable screen for making just this division of the spectrum, so that it would be possible to measure the energy in the two portions of the spectrum directly and as a whole, without a resort to the extremely difficult and troublesome measures of the energy in separate spectrum lines, a task of great delicacy when discontinuous have to be compared with continuous spectra. After considerable investigation a suitable medium was found in the socalled Euphos glass. This glass, which has been strongly recommended by Schanz and Stockhausen as eliminating completely all the harmful rays and which was prepared under the direction of one of them, cuts off the ultra violet spectrum with remarkable definiteness while showing relatively little absorption of the general luminous
Plate 1, b, c, d, shows the nature of this absorption very clearly. Spectrogram b of this Plate is the spectrum of the mercury quartz arc put on merely for reference, the group at 365 μu being at the right of the figure and the brilliant green line exactly in the centre of the plate. Spectrogram c shows the spectrum of the magnetite arc which is very rich in the ultra violet and d shows the same as absorbed by a Euphos glass screen 2 mm. thick. The exposure in each case was one minute with a rather wide slit and a very brilliant grating. The cut off of the shorter wave lengths by the Euphos glass in the ultra violet is very clean and sudden at wave length 390 μu, practically just at the end of the visible spectrum as seen by the average eye. The