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 μμ, 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 or 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 μμ, 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 μμ and in old persons in whom the lens gets slightly yellow even as far as wave length 420 μ. 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.2 Other writers like Best and Voege 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. 3 5 A third group, of which Birch-Hirschfeld is a representative, holds an intermediate view. It should be noted that the permanent 4 1 Klin. Monatsbl. f. Augenheilk., Dec. 1909. 2 Ztschr. 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. - Having 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 rays. 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 μμ being at the right of the figure and the brilliant green line exactly in the centre of the plate. Spectrogram e 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 absorption continues slightly on into the violet, gradually fading away until the transmission becomes nearly complete for the bright blue mercury line (435 μμ). In examining b, c and d of Plate 1 it must be remembered that the second order ultra violet overlaps the first order so that the group near 365 μμ appears in the first order at the extreme right of the figure and in the second order at the extreme left. In d of this Plate the arc spectrum fades off on the left, not from absorption but from the weakening of the photographic action. The Euphos glass is extremely transparent to the radiations throughout all except the extreme violet of the visible spectrum, and well into the infra red, as will hereafter be seen. The results here obtained for its absorption of the ultra violet are altogether parallel with those shown in the paper by Schanz and Stockhausen and also by Hallauer. The Euphos glass thus enables a particularly clean partition of the visible spectrum from the ultra violet and extreme violet to be made. If it were possible to obtain an equally good absorbent for separating the infra red from the visible spectrum radiometric measurements of efficiency would be greatly facilitated. It should here be noted that Euphos glass appears in various shades and some imitations of it are now upon the market, so that a sample of such glass should be tested in the spectrograph before use for such a purpose as the present, inasmuch as in some of the shades the cut-off of the ultra violet is much less sharp and complete. The sample here used was the original No. 1, 2 mm. thick. Method of Investigation. The method taken for the evaluation was the familiar one of measuring the radiation directly by means of a thermopile connected with a sensitive galvanometer in a manner familiar in recent experiments on the efficiency of illuminants in the. visible spectrum, e. g., Lux, Féry. The thermopile was chosen as the radiometric instrument merely as a matter of convenience. The instrument actually used was a Rubens linear thermopile, having 20 constantin-iron couples with a total resistance of 4.6 ohms. It was mounted as shown in Figure 1, in a vacuum tube with a quartz window immediately in front of the couples. The inner body of the instrument, containing the couples, was taken out of its original mounting and set up in a tube about 37 mm. in diameter, through the upper end of which was sealed a pair of leading-in wires. Zts. f. Augenheilk., May 1910, Table VII, figure 3. |