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COLOURED LENSES AND CAR DRIVING
Author(s) -
Clark Barry A. J.
Publication year - 1971
Publication title -
acta ophthalmologica
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.534
H-Index - 87
eISSN - 1755-3768
pISSN - 1755-375X
DOI - 10.1111/j.1755-3768.1971.tb08662.x
Subject(s) - citation , library science , operations research , computer science , engineering
To the Editor Berggren (1) discussed some effects relating to the use of coloured glasses in car driving, and cited some of the previous work on the subject. A few points arising from his paper are discussed here: 1. Berggren claimed that a percentage absorption quoted for a coloured lens -suggests an even transmission and is misleading if that is not the case”. The absorption of a lens is the coinplement of the luminous transmittance (or luminous transmission factor, 13. S. 352 1 : 19(i2), an internationally recognized quantity that relates only to the fraction of incident luminous flux transmitted by the lens, regardless of the variations in the spectral transmittance values of the lens. The use of percentage absorption has been criticized ( 2 ) , but only on the grounds of possible confusion with the luminous transmittance expressed as a percentage. 2. Berggren tested the effect on Nagel anomaloscope readings when subjects observed through coloured lenses. Descriptions of at least two similar experiments have been available for some time (3, 4). Such experiments would be more valuable i f evidence could be produced to show that results obtained under anomaloscope conditions (small bright field with extensive dark surround) have any validity at all for conditions of an extensive daylit scene in which chromatic adaptation modifies the appearance of the scene viewed through coloured lenses. In this type of experiment, the change in mean settings is entirely calculable i f the anomaloscope’s spectral energy distributions and the lens transmittance values are known, so that it is possible to avoid using experimental subjects a t all. Alternatively, if the test is intended to give some idea of a lens transmittance curve, then the anomaloscope’s spectral energy distributions should be taken into account. The increases in ranges of adjustment found when Berggren tested the denser glasses are probably a direct result of the reduced luminances of the anomaloscope test-fields. There seems to be no mention of how these luminances compare with those occurring when sunglasses are normally worn. Certainly, when coloured lenses cause a colour-normal’s