NUMERICAL-ANALYTICAL MODEL OF THE LUMINANCE FACTOR OF AN ARBITRARY SURFACE

Road safety is determined by the distribution of luminance created by asphalt concrete surfaces. On the one hand, experimental determination of the bidirectional reflectance distribution function is laborious, on the other hand, for some angles this task is difficult. The authors propose to use both analytical and statistical models of the luminance factor, which allow determining the luminance factors or coefficients for arbitrary angles of incidence and sighting. The models are based on the idea of a plane-parallel layer, in the volume of which radiation scattering occurs. With correctly selected optical properties of the layer (the optical thickness of the medium, the albedo of single scattering, the phase function of the particles included in the composition), the models allow obtaining reliable results, which was confirmed when compared with the measurement results. The models can also be applicable not only for asphalt concrete pavements, but also for any other surfaces.

Visual and non-visual properties of filters manipulating short-wavelength light

Optical filters and tints manipulating short-wavelength light (so-called “blue-blocking” or “blue-attenuating”) are used as a remedy for a range of ocular, retinal, neurological and psychiatric disorders. In many cases, the only available quantification of the optical effects of a given optical filter is the spectral transmittance, which specifies the amount of light transmitted as a function of wavelength. Here, we propose a novel physiologically relevant and retinally referenced framework for quantifying the visual and non-visual effects of these filters, incorporating the attenuation of luminance (luminance factor), the attenuation of melanopsin activation (melanopsin factor), the shift in colour, and the reduction of the colour gamut (gamut factor). We examined a novel data base of optical transmittance filters (n=120) which were digitally extracted from a variety of sources and find a large diversity in the alteration of visual and non-visual properties. We suggest that future studies and examinations of the physiological effects of optical filters quantify the visual and non-visual effects of the filters beyond the spectral transmittance, which will eventually aid in developing a mechanistic understanding of how different filters affect physiology.

Spatial sensitivity, responsivity, and surround suppression of LGN cell responses in the macaque

Responses of cells in the lateral geniculate nucleus (LGN) of the macaque monkey have been measured for different sizes of chromatic and achromatic stimuli, with relative luminance spanning a range of 3–6 log units. Homogeneous illuminated test fields, centered on the receptive field, were used. Responses to these stimuli deviated from what is expected for the grating stimuli used to study the contrast-sensitive mechanisms in the visual pathway. For test fields smaller than the center of the receptive field, both the excitatory and the inhibitory cone-opponent components were present in the response, and the sensitivity to both components increased with the same factor when the test field increased in size (area summation). For test field areas extending into the suppressive surround of the extraclassical receptive field, the excitatory and the inhibitory cone opponents were both suppressed, again by the same factor. This suppression of the cell’s responsiveness, as a function of test spot area, was described by a logarithmic function, and the spatial sensitivity of attenuation could therefore be described by a power function of radius. The logarithmic suppression was clear for parvocellular and koniocellular cells but was more prominent for magnocellular cells. The surround field suppression was also found for the prepotential inputs to LGN cells, indicating a retinal origin. The difference of Gaussian (DOG) model has been used successfully to describe the cells’ contrast behavior for grating stimuli. However, this model fails to describe the constant excitatory/inhibitory response balance needed to obtain color (hue) stability for light stimuli of different sizes but with the same Commission Internationale de l’Eclairage (CIE) chromaticity and luminance factor. Neither the constant responsiveness found in the center of the receptive field nor the suppressive response in the surround can be described by the DOG model.