LIGHTING PROBLEMS IN HIGHWAY T R A F F IC Proceedings of a symposium held at the Wenner-Gren Center, Stockholm Sweden, October 1962 Edited by ERIK INGELSTAM The Royal Institute of Technology, Stockholm, Sweden SYMPOSIUM PUBLICATIONS DIVISION PERGAMON PRESS OXFORD · LONDON · NEW YORK · PARIS 1963 PERGAMON PRESS LTD. Headington Hill Hall, Oxford 4 & 5 Fitzroy Square, London, W.\ PERGAMON PRESS INC. 122 East 55th Street, New York 11, N. Y. GAUTHIER-VILLARS ED. 55 Quai des Grands-Augustins, Paris 6 PERGAMON PRESS G.m.b.H. Kaiserstrasse 75, Frankfurt am Main Distributed in the Western Hemisphere by THE MACMILLAN COMPANY - NEW YORK pursuant to a special arrangement with PERGAMON PRESS LIMITED Copyright © 1963 PERGAMON PRESS LTD. Library of Congress Card No. 63—18135 Printed in Great Britain by Charles Birchall & Sons Ltd. Liverpool and London OPENING ADDRESS PROFESSOR Y. ZOTTERMAN Vice-President of The Swedish Road Safety Council WE have gathered here to discuss for some days lighting problems in high­ way traffic. This includes a very complicated system of problems of greatest importance for road safety during dark hours, which in this country may extend over most of the day in wintertime. Man, like the higher animals, rely, with regard to their reactions to light and to optical signals, on the photoceptive apparatus of our eyes and the neural mechanisms connected with them. The properties of this system have developed during the passage of a million years. During this long period of evolution our visual system has been adapted to our environment. In a primitive life the change from daylight via dusk to night takes at least three-quarters of an hour. It is interesting to note that complete dark adaptation takes about 45 min. Now man recently has developed the habit of rushing about in the night at highspeed on our roads focusing bright headlights into the dark adapted eyes of other fellows also driving at high speed, blinding them for several seconds, during which period they may travel fully blinded 50-100 m. The problems we meet in night traffic are manifold, but they all depend, in the last hand, on the peculiar properties of our visual organs, and can only be solved by adapting our lighting technically to the physiological properties of our eyes. For that reason a conference of this kind, where physicists, technologists, psychologists and physiologists meet, should provide the right forum for discussing the lighting problems in highway traffic. We are confident that you here will be able to define the principal ways to solve these problems which are most important for the safety of man in traffic. The Swedish Road Safety Council extends to you a hearty welcome. We are delighted to see that so many famous experts in different fields of lighting research have accepted our invitation to attend this meeting. 1 THE GLARE-EFFECT FROM THE STANDPOINT OF PHYSIOLOGICAL OPTICS HERBERT SCHOBER Institut für medizinische Optik der Universität München THE information capacity of the human eye is dependent on physical, physiological and psychological factors. The most important physical moment is given by the scattering of light in the optical media passed by the rays, i.e. the cornea, the eye-lens and the vitreous body of the eye bulb and also—a cause which is easily forgotten—in the glasses of goggles or correction spectacles. It is well known that persons wearing eye glasses and also older people are much more sensitive to glare effects than no-glass- wearers and younger people. The interpretation of these connections is not difficult. The amount of glare-sensitivity is caused by loss of photometrical Ptantëg· of Poopio Hë¥in§ Visusl Oofo€ts 90 50 70 60 50 40 30 20 90 0 , . . , , 20 30 40 50 60 70 Years - **t FIG. 1. Percentage of visual defected persons in connection with age. 3 4 HERBERT SCHOBER contrast, also by physical moments. If we look at Fig. 1 we can see that the probability of eye-defects is increasing with the age of life. All lesions on the cornea causing permanent stigmas become centres of diffraction figures or stray-light centres. A similar connection can be found in the eye-lens, in the vitreous body and in the nervous and static fibres of the retina. An increase of glare-effects in the middle or higher age of life shows the ophthal­ mologist very often the beginning of several eye-diseases such as cataracts, glaucoma, iritis, etc. Although most of the phenomena described here are pathologic ones and caused by curable or incurable eye-diseases, these facts must also be well-known to the non-physician. Especially in this case it should not be forgotten that an increasing glare-sensitivity is given in higher ages. Concerning the diminution of contrast at eye-glass-wearers we can find two causes. The first one is given by the scattering of light in the glasses. All damage in the surfaces of these glasses and all soiling effect a very remarkable increase of glare. If an eye is not or act well corrected the images on the retina are more or less unsharp. The image figure of a single object point is larger than in normal cases and influences therefore as a diminution of contrast the image figures of the neighbour points. By adding the physical and the medical causes we get an interesting result for glass-wearers: if a person has a higher glare-sensitivity, or if the recovering times after disappearing of glare sources is considerably higher than in normal cases, we should send this person to an ophthalmologist who is well acquainted with such problems. He can find out the causes and can prescribe the best eye-glasses. He should also give recommendations, that such a person should drive carefully at night and especially at twilight, i.e. in the evening after sunset or in the morning. It should not be forgotten that during these hours all con­ trast change. In daylight the sky is clear and the highway is dark. At night we see the road much clearer than the sky. Therefore there must always exist a moment when the contrast changes and another short moment when it is nearly zero. This situation can cause some optical illusions, as is seen by Fig. 2, where the direction of the flying birds changes between day and night. The same requirements are given for these drivers, if the contrasts in daylight decrease, namely in foggy weather. It is important to make public information about the above-mentioned facts, as more and more people with glare-defects are occupied as drivers. Also road-engineers should consider this important problem. We should do our best to make all street borders well recognizable in all illumination conditions. Since a few years, black roads with white border-markations, possibly even with reflecting pillars, were constructed in Europe. All drivers recognize this advantageous fact, when they once have to change from such a modern street to an older THE GLARE-EFFECT FROM THE STANDPOINT OF PHYSIOLOGICAL OPTICS n o cti e r di e Thht. 3). nig 95d 1n oL y a ha cd syn Pe al we urnbet her, Johange cc C. Esms to M.e e (s n s od atibir ginng mayi al ihe fl pticof t O 2. G. FI 6 HERBERT SCHOBER one. Only in this connection can the very often discussed question with re­ gard to illumination techniques be understood, whether the light or dark glare effects should be preferred. In the same connection we should under­ stand that a chessboard at the surface of a road is always bad. Such a chessboard is very often caused by repairs of a clearer road with black material. It gives wrong information and means—expressed in terms of the information theory—an increasing of the optical noise. FIG. 3. Generalized Weber-Fechner's law: visibility of relative luminance differences at different luminance levels, The physiological causes for glare-effects are less clear. The physiologists differ between absolute glare, relative glare and adaptation glare. Absolute glare occurs only when the average luminance in the visual field is higher than about 20,000 cd/m2. This is, for instance (Fig. 3), the sunny street but also the road at noon-time, when the sky is overcast. In this case, sunglasses will be the only help. Its absorption might be 50 per cent. There is only one requirement: sunglasses should not destroy the visual acuity. They should be adjusted to the refraction power of the wearer. Therefore all sunglasses for a driver should be chosen as carefully as other correction glasses. In the last few years a lot has been published about sunglasses. If we realize the above-mentioned facts, such glasses will mostly be used for persons with anomalous refraction, where the filtering effect is reached by coating. The couches of these glassses fix very well so that there is no danger of destruction. If no optical effect is required, also well-chosen blown glasses THE GLARE-EFFECT FROM THE STANDPOINT OF PHYSIOLOGICAL OPTICS 7 or plastics can be used. Polarization filters avoid the absolute glare and a considerable part of the refraction glare on sunny and wet streets. The relative glare is produced by luminance-irregulations in the visual field. It represents undoubtedly the most frequent form, but its control is the most complicated one. Goggles do not help here at all and it is an inexcusable mistake to recommend some kind of goggles for driving at night. If you do so, you decrease not only the luminance in the field of glare source but also the luminance in the visual field. Also glasses with a variable or discontinuous absorption are useless in practice, because they presume static relations, which we do not have in a moving car. It would go too far to discuss all relationships of relative glare. This is not necessary, as all these questions will be discussed in other papers. I would like to bring only one fact to your attention which is a real medical one, namely that the individual sensitivity for relative glare is higher in those cases where turbidities of eye-medium and certain retinal defects are in question. It is possible that in such pathological cases the relative glare can be influenced by certain drugs. Exact information cannot be made yet as to all drug effects, but there is no doubt that we can reach very good corrections with Privin and other similar substances. As to the normal eye such investigations had only unimportant or no results at all. 0.5 0.7 1.0 1.4 2 3 5 7 10 H 20 THRESHOLD SIZE (MINUTES) FIG. 4. Dependence of the contrast threshold from the size of visual objects (M. Luckish, Light, Vision and Seeing, Nostrand new edit. 1944). 8 HERBERT SCHOBER As we can see by Fig. 4 there exists a very strong connection between the size of a visual task and its relative contrast to the surrounding field. Hyperbolic borderlines separate the visible world of visual task from the invisible world. The border lines change with the luminance in the visual field. This fact results from the law of Weber-Fechner. The higher the luminance level the larger the area of visual world. By all amelioration of the luminance level in the visual field we gain many visible objects which are invisible at a worth luminance level. By this reason a luminance level in the visual field is required as high as possible. Therefore all street illumina­ tions are better than the use of headlights on an illuminated road. Figure 4 also demonstrates another result. If a visual task is invisible we can make it visible by enlarging the size of the objects or by increasing the contrast to the surrounding field* As we cannot influence the size of the visual objects in night driving we can only ameliorate the contrast. That can be done on the objects. A very good example is the white helmet of the motor­ cycle drivers. Moreover, all better eye-correction, all cleaning of eye­ glasses and wind-screens—I guess—should have a much higher influence on the contrast in all the work we try to do with high costs in special illuminations, etc. 350 400 450 500 800 (pm) Absorption rate of eye glasses FIG. 5. Spectral absorption factors of yellow glasses for television and traffic goggles in foggy weather. THE GLARE-EFFECT FROM THE STANDPOINT OF PHYSIOLOGICAL OPTICS 9 Very often we are told that contrast sensitivity increases in yellow light or by wearing yellow eye-glasses. That may be true from the psychological standpoint. But there is no objective sign for a physiological influence. The physiological contrast function is independent from the colour of light. Yellow eye-glasses give us the impression of sunny weather and a higher luminance than we indeed have. Therefore we have a very good result with yellow eye-glasses for persons whose eyes must be corrected but who normally dô not want to wear eye-glasses, i.e. young ladies, etc. But yellow eye-glasses have also some disadvantages. They absorb mostly all shorter wavelengths in the visible spectrum (Fig. 5). By wearing such glasses we cannot see objects in blue or blue-green colour if the contrast is only a colour contrast and not also a contrast of luminance.' Factories have developed also yellow glasses which do not absorb all short waves, i.e. the "Samina" of the Balzer's factory in Liechtenstein or the Rodenstock "Telecolor". Such glasses are much better than the other ones. Something similar can be said of the adaptation-glare, which is produced —contrary to the relative glare—because of considerable temporal varia­ tions of luminance. We will find here high individual differences especially with regard to the readaptation during glare-period when they close one eye, and by this they are much less sensitive against adaption-glare. Other people, whose relative figure is rather the same, do not succeed, because the after-images—produced in the closed eye—predominate and miscarry the result. Relative glare and adaptation glare are especially attacked by light- technics. Everything must be done to keep the number of glare sources as low as possible and to avoid considerable ^regulations in the visual field on local and temporal arrangement. The good screening of light-sources, the widening of streets, glare-screening as well as illumination of subways have to be seriously considered. Whereas the physical and physiological side of the glare-process can be measured by relatively satisfactory methods, it is impossible with regard to the psychological one. The psychological side concerns especially the subjective glare-impression and the subjective decrease of the information capacity of the visual sense. The American psychologist Blackwell and his research team have published in some papers in Illumination Engineering in the last years some experiments to find out a way of measuring such influences. His publications have caused a sensation all over the world, but of course have sometimes also been contradicted. A final opinion will only be possible if very extensive material is checked. As the experiments and researches of Prof. Blackwell and his co-operators are not known everywhere, it seems to be necessary to give some remarks about his idea. The visual system is, as Prof. Blackwell assumes, a real information-