A New Look at Colour Rendering, Level of Illumination, and Protection from Ultraviolet Radiation in Museum Lighting

TL;DR: A survey of a new generation of passive sensors that are capable of taking into account the overall environmental effects by mimicking in some way the behaviour of real works of art, which represent a new frontier in the environmental control in museums.

TL;DR: In this paper, a spectral aging test was developed to estimate the photochemical damage of oil, acrylic and gouache paints exposed to permanent lighting, and the test was performed using two different irradiation levels in ten exposure series.

TL;DR: A strategy is reported to optimize lighting to reduce photochemical degradation of works of art and archival documents by improving luminous efficiency of the spectral profile to exclude light which doesn't contribute to brightness or color perception, while also trying to maintain color rendering.

Abstract: According to LeGrandl an orange has the same chromaticity as a bar of chocolate. They differ in reflectance. By shining more light on the chocolatethan on the orange, one could make them match both in chromaticity and in luminance, but the chocolate would still not look orange, or vice versa. This tendency of lighted objects to keep many of their perceived characteristics relatively unchanged through quite large changes in the colour and quantity ofincident illumination is known as 'constancy'. Two aspects of constancy, as affected by lighting, have been extensivelystudied:" (a) Brightness constancy, better termed lightness constancy or whiteness constancy. A white sheet of paper still looks white in sunlight or in shadow and does not appear to change in reflectance when the illumination falls. (b) Colour constancy: a green leaf looks green 10 tungsten hght or in the light from a blue sky, despite the difference in the spectra of the two sources. Brightness constancy is an unfortunate term because the words suggest, wrongly, that apparent brightness stays constant when illumination changes. It is arguable too that brightness constancy is just one aspect of colour constancy. However, throughout this paper the term 'constancy' is used to embrace both effects. For lighting engineers, constancy has been something of an embarrassment. Unquestionably the retinal image is determined by the ambient pattern ofluminance and chromaticity, so neither illumination nor reflectance can register independently of the luminance. Yet when we view a lighted object we find we can estimate its reflectance with confidence to within say 20 per cent and its illumination to within perhaps 50 per cent but its luminance only after a bout of mental arithmetic. It is significant that constancy is generally a property of illuminated objects. If the object is viewed through a reduction tube (a blackened tube with a small aperture) constancy will no longer prevail, and the appearance of the spot of light seen at the end of the tube will depend solely on its chromaticity and luminance, for a change 10 illumination is now indistinguishable from a change in reflectance. However once the reduction tube is removed, two stimuli having the same chromaticity and the same luminance may well look different. A solid will look solid, a liquid will look liquid, and so forth. A number of different 'modes of appearance' in which light or colour can be experienced may be identified;" the following are particularly relevant: (a) the surface mode, in which the stimulus is perceived as the coloured surface of an object; (b) the volume or bulk mode, in which colour is seen in depth behind the surface, as in a coloured transparent medium; (c) the illuminant mode, in which light and colour are perceived as emerging from a selfluminous body, such as a fluorescent lamp; (d) the aperture, or film, mode, typified by the view through a reduction tube, or by a uniform expanse of blue sky. The mode of appearance does not describe the object itself, only the way we experience it. A given object will not always appear in the same mode. An extinguished fluorescent lamp would normally be seen in the surface mode, with a definite reflectance and showing a large measure of constancy; once switched on it would appear in the illuminant mode and its surface characteristics, such as its reflectance, would be impossible to identify. Viewedthrough a reduction tube even its self-luminous nature would be unverifiable; it would be seen in the aperture mode. It is helpful to analyse the perceptual cues on which the modes depend. Thus we perceive in the surface mode when our eyes can focus on the surface itself, distinguishing the tiny gradations of luminance which we have learned to interpret as texture, sheen, convexity, etc. Other The author is with the Department of Architecture, UniversitY of Manchester. This paper has been approved for publication by the IES PapersCommittee by whom it was first received on January 3, 1970 and in final form on July 6, 1970. It was presented at a meeting of the SocietY in London on September 23, 1970