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Borate Phosphor
Published in S. K. Omanwar, R. P. Sonekar, N. S. Bajaj, Borate Phosphors, 2022
A fluorescent lamp is a low-pressure gas discharge light source, in which light is produced predominantly by fluorescent powders activated by ultraviolet radiation generated by discharge in mercury. The lamp, usually in the form of a long tubular bulb with an electrode at each end, contains mercury vapour at low pressure with a small amount of inert gas for starting. Figure 6.2 demonstrates operation principle of a fluorescent lamp [4]. The majority of the emission (95%) takes place in the ultraviolet (UV) region and the wavelengths of the main emission peaks are 254 nm and 185 nm. Hence, the UV radiation is converted into light by a phosphor layer on the inside of the tube. Since one UV-photon generates only one visible photon, 65% of the initial photon energy is lost as dissipation heat. On the other hand, the final spectral distribution of emitted light can be varied by different combinations of phosphors. Correlated colour temperatures (CCT) vary from 2,700 K (warm white) and 6,500 K (daylight) up to 17,000 K and colour rendering indices (CRI) from 50 to 95 are available. The luminous efficacy of the latest T5 fluorescent lamp is up to 100 lm/W (without ballast losses). Dimming is possible down to 1% of the normal luminous flux, and with special high-voltage pulse circuits down to 0.01%.
Photonic Nanodevices and Technologies against Light Pollution
Published in Tuan Anh Nguyen, Ram K. Gupta, Nanotechnology for Light Pollution Reduction, 2023
Elisangela Pacheco da Silva, Elizângela Hafemann Fragal, Ederson Dias Pereira Duarte, Sidney A. Lourenço, Edvani C. Muniz, Thiago Sequinel, Rafael Silva, Eduardo José de Arruda, Vanessa Hafemann Fragal
The wavelength is responsible to determine the color in visible light, which can be monochromatic – a single wavelength – or polychromatic – multiples wavelengths. Color is a fundamental perception of the human eye (our light sensor) and this perception is changed by the environment and conditions to which humans are exposed. The chromatic characteristic of light is divided into correlated color temperature (CCT – given in degrees of Kelvin) and color reproduction index (CRI). The CCT range of artificial light is from 2,000 K (warm) up to 10,000 K (cool), as shown in Figure 13.1b. Meanwhile, the CRI (%) represents the ability of a light source to accurately reproduce the colors of the object it illuminates. As higher the index as accurate is the reproduction [4].
Lighting
Published in Stephen A. Roosa, Steve Doty, Wayne C. Turner, Energy Management Handbook, 2020
Eric A. Woodroof, Stan Walerczyk, Fred Hauber
The coordinated color temperature (CCT) describes the color of the light source. For example, on a clear day, the sun appears yellow. On an over-cast day, the partially obscured sun appears to be gray. These color differences are indicated by a temperature scale. The CCT (measured in degrees Kelvin) is a close representation of the color that an object (black-body) would radiate at a certain temperature. For example, imagine a wire being heated. First it turns red (CCT = 2000K). As it gets hotter, it turns white (CCT = 5000K) and then blue (CCT = 8000K). Although a wire is different from a light source, the principle is similar.
Dry gelatin ‘Photo-mechanical’ plates – their significance in the evolution of scientific & technical photography
Published in The Imaging Science Journal, 2023
The lighting sources utilized at the time were driven by the energy sources available locally. Gas lighting was in use at this time, either from acetylene generators or from mains gas supplies. The latter had become more attractive when Carl Auer von Welsbach introduced the Welsbach light, now known as the gas mantle [18]. Both these gas lighting technologies were capable of bright but somewhat yellow light. This is best quantified by the Correlated Colour Temperature (CCT) of the light source, a measure now commonly used to describe the output of domestic and museum light bulbs. By this measure acetylene lamps delivered only 3200 K and gas mantles even lower at around 2100 K [14,19]. As these photographic materials were only sensitive to shorter (blue) wavelengths these rather yellow illuminants were somewhat inefficient.
Improved Methods for Computing CCT and D uv
Published in LEUKOS, 2023
Yue Li, Cheng Gao, Manuel Melgosa, Changjun Li
Because it is a single number, CCT is simpler to communicate than SPD, which has led the lighting industry to accept CCT as a shorthand means of reporting the color of nominally white lights emitted by electric light sources. CCT values are intended by the lighting industry to give a general indication of the apparent “warmth” or “coolness” of the light emitted by a source. Both the distance and direction of a color shift from the Planckian locus (denoted by ) are important. In fact, in 2008 the American National Standards Institute (ANSI 2008) indicated that must be reported. The use of CCT and provides an exact specification of the chromaticity of a white light source, and these two numbers can replace the chromaticity coordinates u, v in test reports and the specification of data. Furthermore, CCT is used to compute the color rendering and color fidelity indices (CIE 015 2018). For many lighting applications in offices, hotels, galleries, textile industry, etc., CCT and the color rendering/fidelity index are the two most important factors governing the choice of appropriate light sources.
Tutorial: Background and Guidance for Using the ANSI/IES TM-30 Method for Evaluating Light Source Color Rendition
Published in LEUKOS, 2022
Correlated color temperature (CCT) is calculated as the color temperature of the Planckian radiator nearest the chromaticity coordinates of the test source. It is calculated in the CIE 1960 (u, v) chromaticity diagram, which is a legacy of when it was developed as measure (Robertson 1968). It indicates whether the apparent color is warmer (lower CCT) or cooler (higher CCT). For interior architectural lighting applications, sources typically range between 2700 K and 6500 K. Importantly, two light sources with the same CCT can have different chromaticities and not match in appearance, as illustrated in Fig. 4. This is addressed with a complimentary measure called Duv, which is a measure of the distance between the chromaticity of the light source and that of the nearest Planckian radiator in the CIE 1960 (u, v) chromaticity diagram (Ohno 2013) – the same Planckian radiator used to calculate CCT. Duv conveys the relative greenness (more positive values) or pinkness (more negative values) of the light. CCT and Duv provide a complete specification of chromaticity, with axes that are more closely linked to a visual perception.