Light-emitting diodes (LED) for domestic lighting: any risks for the eye?

Light-emitting diodes (LEDs) are taking an increasing place in the market of domestic lighting because they produce light with low energy consumption. In the EU, by 2016, no traditional incandescent light sources will be available and LEDs may become the major domestic light sources. Due to specific spectral and energetic characteristics of white LEDs as compared to other domestic light sources, some concerns have been raised regarding their safety for human health and particularly potential harmful risks for the eye. To conduct a health risk assessment on systems using LEDs, the French Agency for Food, Environmental and Occupational Health & Safety (ANSES), a public body reporting to the French Ministers for ecology, for health and for employment, has organized a task group. This group consisted physicists, lighting and metrology specialists, retinal biologist and ophthalmologist who have worked together for a year. Part of this work has comprised the evaluation of group risks of different white LEDs commercialized on the French market, according to the standards and found that some of these lights belonged to the group risk 1 or 2. This paper gives a comprehensive analysis of the potential risks of white LEDs, taking into account pre-clinical knowledge as well as epidemiologic studies and reports the French Agency's recommendations to avoid potential retinal hazards.

[Neurophysiological basis and clinical tests for assessment of X-linked color vision deficiencies in school children]. / Comprendre et tester les déficiences de la vision des couleurs de l'enfant, en pratique.

Vision screening of school children at 5-6 years of age must include color vision screening. X-linked dyschromatopsia is the most frequent disorder affecting 8% of boys and 0.4% of girls. This paper presents the physiology of these deficiencies caused by an alteration of the spectral absorption properties of one of the cone pigments (protanomalous or deuteranomalous trichromats) or the absence of one of the pigments (protanopia or deuteranopia), the most frequent. Absence of two of the pigments (blue cone monochromacy) is very rare and differs from achromatopsia. The physiological basis of the main tests for easy clinical screening are presented. Testing methods designed for children are reviewed. The Ishihara test is the most widely used screening test specific for congenital color defects. If the plates are correctly read, the child has normal color vision. If not, arrangement tests such as Panel D 15 and desaturated Panel D 15 tests can be used to diagnose the type of the defect (protan or deutan) and grade the degree of color deficiency according to a strategy adapted to children. Examples of results are presented for each axis along which caps are confused, providing a quick and easy preliminary diagnosis. Early detection of color vision malfunction in children allows parents and teachers to make necessary adjustments to the teaching methods for appropriate learning.

Fruits, foliage and the evolution of primate colour vision.

Primates are apparently unique amongst the mammals in possessing trichromatic colour vision. However, not all primates are trichromatic. Amongst the haplorhine (higher) primates, the catarrhines possess uniformly trichromatic colour vision, whereas most of the platyrrhine species exhibit polymorphic colour vision, with a variety of dichromatic and trichromatic phenotypes within the population. It has been suggested that trichromacy in primates and the reflectance functions of certain tropical fruits are aspects of a coevolved seed-dispersal system: primate colour vision has been shaped by the need to find coloured fruits amongst foliage, and the fruits themselves have evolved to be salient to primates and so secure dissemination of their seeds. We review the evidence for and against this hypothesis and we report an empirical test: we show that the spectral positioning of the cone pigments found in trichromatic South American primates is well matched to the task of detecting fruits against a background of leaves. We further report that particular trichromatic platyrrhine phenotypes may be better suited than others to foraging for particular fruits under particular conditions of illumination; and we discuss possible explanations for the maintenance of polymorphic colour vision amongst the platyrrhines.

Frugivory and colour vision in Alouatta seniculus, a trichromatic platyrrhine monkey.

It is a long-standing hypothesis that primate trichromacy evolved to help fruit-eating primates find fruits amongst leaves. We measured the reflectance spectra of fruits eaten by a trichromatic primate, Alouatta seniculus, in the rainforest of French Guiana, as well as those of the leaves that form the natural background to fruits. We develop a method of specifying these natural colour signals in a chromaticity diagram appropriate for A. seniculus. By treating the task facing frugivorous monkeys as a signal detection task, we show that the spectral tuning of the L and M cone pigments in A. seniculus is optimal for detecting fruits amongst leaves.

Computerized simulation of color appearance for dichromats.

We propose an algorithm that transforms a digitized color image so as to simulate for normal observers the appearance of the image for people who have dichromatic forms of color blindness. The dichromat's color confusions are deduced from colorimetry, and the residual hues in the transformed image are derived from the reports of unilateral dichromats described in the literature. We represent color stimuli as vectors in a three-dimensional LMS space, and the simulation algorithm is expressed in terms of transformations of this space. The algorithm replaces each stimulus by its projection onto a reduced stimulus surface. This surface is defined by a neutral axis and by the LMS locations of those monochromatic stimuli that are perceived as the same hue by normal trichromats and a given type of dichromat. These monochromatic stimuli were a yellow of 575 nm and a blue of 475 nm for the protan and deutan simulations, and a red of 660 nm and a blue-green of 485 nm for the tritan simulation. The operation of the algorithm is demonstrated with a mosaic of square color patches. A protanope and a deuteranope accepted the match between the original and the appropriate image, confirming that the reduction is colorimetrically accurate. Although we can never be certain of another's sensations, the simulation provides a means of quantifying and illustrating the residual color information available to dichromats in any digitized image.

Reversal in the sequence of the Benham colours with a change in the wavelength of illumination.

A Benham disk was rotated at 7 c/sec and illuminated by monochromatic lights from the range 534-586 nm. The elicited colours of the rings were described either with a colour naming procedure or by matching with a Munsell chip. Exchanges of hues between the two extreme rings and between the two inner rings were reported around 557 and 566 nm by the colour naming procedure, thus resulting in a hue reversal in the spatial display of colours. Similar hue shifts were also reported with the matching procedure. The effect of a possible displacement in the equilibrium of colour-opponent cell population, resulting from chromatic adaptation, is discussed.

Brightness matching and flicker photometric data obtained over the full mesopic range.

Three normal observers made visual matches from 0.03 to 100 td on a 10 degree central field at 445, 560 and 630 nm, using two different methods: heterochromatic flicker photometry and direct comparison brightness matching. In a relative sensitivity vs illuminance plot, the brightness matches underwent smooth changes, while the flicker curve exhibited a step-like transition around 1 td, between two separate branches. A reverse Purkinje shift was found on the high mesopic branch at 630 nm, possibly due to cone-cone interactions, and on the low mesopic branch at 445 nm, with questionable origin. At 630 nm and 0.03 td, both methods yielded matches that were not truly scotopic but might not have addressed the same mechanisms.

Relations between inter- and intra-individual variability of color-matching functions. Experimental results.

Color-matching functions, as well as the variances and inter- and intra-individual correlations, are given for ten subjects. The dispersion found in the blue region is greater than that indicated by Stiles and Burch. The color-matching technique used is thought to be the cause. Consequences of intra-individual variability are evaluated. A comparison is made with scores of subjects on the Davidson and Hemmendinger color rule. The chromaticity diagram is shown to give an unsatisfactory representation of individual variations.