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Understanding Light:
Published in Michael Stiller, Quality Lighting for High Performance Buildings, 2020
Illuminance is the amount of light per unit area that is projected onto a given surface, while luminance is the amount of light per unit area that is emitted or reflected back to the viewer from a given surface. Illuminance has both a metric and imperial expression. The metric expression, lux, is the measure of the amount of light, or number of lumens, that falls onto a surface the size of a square meter; and the imperial expression, foot-candles, is the amount of light that falls onto a surface the size of a square foot. Both the illuminance on a surface and the luminance of a surface will vary as the distance is varied between the surface and the source of light, as they are both dependent on the concentration of light, or lumens, that falls that surface. As we have demonstrated with our flashlight, the number of lumens falling on a given area will decrease as we move our light source farther from the object being lit, and the beam, made up of a constant number of lumens, spreads out to cover a greater and greater area. The luminance of a surface will also be affected by other factors, namely that surface’s translucence (in the case of back-lit materials), reflectance (or color) and specularity (or glossiness).
Environmental Ergonomics
Published in Robert W. Proctor, Van Zandt Trisha, Human Factors in Simple and Complex Systems, 2018
Robert W. Proctor, Van Zandt Trisha
An evaluation of lighting conditions in a home or work environment must begin with the measurement of effective light intensity, or photometry (Kitsinelis, 2015). However, we must distinguish between light that is reflected from and light that is generated by a surface on which the measurement is made. Illuminance is the amount of light falling on a surface, and luminance is the amount of the light generated by a surface (either a light source or a reflection). Both luminance and illuminance are determined by luminous flux, which is measured in units called lumens. Lumens represent the amount of visible light in a light source and thus the power of the light source corrected for the spectral sensitivity of the visual system. Illuminance is the amount of luminous flux per unit area (one square meter), and luminance is the luminous flux emitted from a light source in a given direction. The luminance of a reflection is a function of both the illuminance and the reflectance of a surface.
Color in Digital Cinema
Published in Charles S. Swartz, Understanding Digital Cinema, 2004
In all color reproduction systems, gamut is a function of luminance. As luminance increases toward white, the available range of chromaticity values in (x, y) or (u’, v’), or chroma values in (a*, b*) or (u*, v*) decreases. Color gamut should be considered in 3-space; a 2-dimensional plot is not sufficient to appreciate the luminance dependence. As an example, in Rec. 709 RGB, available chromaticity values encompass the entire triangle whose vertices correspond to the primary chromaticities at relative luminance up to 0.0722. However, luminance can exceed 0.0722 only through some contribution from red or green, and that precludes displaying pure blue. At luminance values above 0.2126, pure red is unavailable, and at luminance values above 0.7154, pure green is unavailable. As luminance approaches 100%, only a small color range in the vicinity of white is available.
Improving illuminance performance by implementing a kinetic façade system: case study of office building in Dubai
Published in Journal of Asian Architecture and Building Engineering, 2023
Luminance is a photometric measure of the luminous intensity per unit area of light travelling in a given direction. It describes the amount of light that passes through, is emitted, or is reflected from, a particular area, and falls within a given solid angle. Selected for this purpose are the lux performance on 15th August at 9:00 am from the east direction, 15th March at 5:00 pm from a west direction, and 15th January at 1:00 pm from a south direction. Table 8 presents the results in terms of luminous intensity performance with the cd/m2 units. Based on the Table 8, the luminance value reduced especially at 9:00 am and 1:00 pm, this minimised the variation which indicates low contrast and helped to achieved uniformity ratio of light distribution which also indicates better visual comfort. Studies (Suk 2019) stated that for the background lighting on the walls the maximum luminance should be limited to 1000 cd/m2 a luminance on the ceiling of 250–500 lux is perceived as comfortable, this means the kinetic case is much better than the base case.
Effect of black level and color gamut on display brightness
Published in Journal of Information Display, 2023
Garam Seong, Youngshin Kwak, Hyosun Kim
The color gamut is related to the Helmholtz-Kohlrauch (H-K) effect, which refers to the increased brightness for colors with the same luminance but a higher chroma. As the color gamut expressible by the display widens, the H-K effect becomes a more important issue for display brightness. Previous studies have explored the H-K effect using various displays [4]. For instance, in the cathode-ray tube (CRT) display, the brightness-matching experiment was conducted with red, green, blue, cyan, magenta, and yellow patches by adjusting the luminance of gray color patches to have the same brightness [5]. Kim et al. [6] and Park [7] examined the lightness in an organic light-emitting diode (OLED) display, liquid-crystal display (LCD), and quantum dot (QD) display using magnitude estimation. Oh et al. demonstrated the H-K effect in complex images with a wide color gamut LCD [8]. Shizume et al. and Nakagawa et al. showed the H-K effect on the brightness of natural images reflecting the H-K effect [9,10].
Improved Particle Swarm Optimization for Detection of Pancreatic Tumor using Split and Merge Algorithm
Published in Computer Methods in Biomechanics and Biomedical Engineering: Imaging & Visualization, 2022
Bhawna Dhruv, Neetu Mittal, Megha Modi
Contrast: For different types of images, the difference in luminescence that makes an object visible is known as contrast, and it may be computed as the illumination difference between two objects. The variation in colour that initiates object presentation is called contrast (Dhruv et al. 2019). Contrast is calculated in the actual world by comparing the luminance of an object to other objects in the same visual field. The image has low entropy and weak contrast when the difference between its maximum and minimum intensities is relatively small. The contrast ratio is defined as the image’s highest level of contrast. The idea is to boost an image’s contrast so that it is easier to understand. The contrast is a proportion of Luminance difference/Average luminance of the type. This also implies that if the average luminance is high, a minor difference can be overlooked, however if the average brightness is low, the difference cannot be overlooked. Contrast may be computed using the equation 8.