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Light
Published in John Watkinson, Convergence in Broadcast and Communications Media, 2001
The human visual system (HVS) has evolved to be sensitive to a certain range of frequencies which we call light. The frequencies are extremely high and it is the convention in optics to describe the wavelength instead. Figure 6.2 shows that the HVS responds to radiation in the range of 400 to 700 nanometres (nm = m × 10–9) according to a curve known as a luminous efficiency functions having a value defined as unity at the peak which occurs at a wavelength of 555 nm under bright light conditions. Within that range different distributions of intensity with respect to wavelength exist, which are called spectral power distributions or SPDs. The variations in SPD give rise to the sensation that we call colour. A narrowband light source with a wavelength of 400 nm appears violet and shorter wavelengths are called ultra-violet. Similarly light with a wavelength of 700 nm appears red and longer wavelengths are called infra-red. Although we cannot see infra-red radiation, we can feel it as the sensation of heat.
Patterns of Daylight Illumination
Published in Lisa Heschong, Visual Delight in Architecture, 2021
Most people learn in elementary school about how, as a young man, Sir Isaac Newton discovered that sunlight is composed of ‘all the colors of the rainbow,’ by placing a glass prism in the path of a beam of sunlight. To confirm that the rainbow was a property of the light and not the glass, he then placed a second prism in the path of the rainbow’s light and turned the rainbow back into a beam of white sunlight. Newton’s discovery dramatically opened up the field of physics and the study of light. Today we have spectrometers, sensitive instruments that can measure the intensity of each band of electromagnetic wavelengths that are contained within a given light source. The readings from a spectrometer are called the spectral power distribution (SPD for short). An SPD graph shows the intensity of each wavelength contained in a source of light or the reflection of light from an object, which is key to understanding the color properties of various types of light. Together, Figures 7.3 and 7.4 allow you to compare the color content of daylight and candlelight to three common electric light sources. We have also added the standard photopic response curve (shaded gray), which is used to transform these SPD graphs into lux values, and the ipRGC, or melanopic, sensitivity curve (shaded blue) to compare circadian stimulus potential.
Color fundamentals for digital imaging
Published in Sharma Gaurav, Digital Color Imaging Handbook, 2017
Our current understanding about the nature of light and color can be traced to the work of Sir Isaac Newton.215 Newton’s careful experiments215,216 with sunlight and a prism helped dispel existing misconceptions and led to the realization that light can be decomposed into a spectrum of monochromatic components that cannot be further decomposed. Accordingly, light is characterized physically by its spectral composition. Typically, the characterization takes the form of a spectral power distribution (SPD), which characterizes light by the distribution of power (or energy per unit time) as a function of wavelength.†
Consideration of Light Level in Specifying Light Source Color Rendition
Published in LEUKOS, 2020
Minchen Wei, Wenyu Bao, Hsin-Pou Huang
Color preference, an important dimension of light source color rendition, has been of practical interest for decades. Manufacturers, specifiers, and designers would like to produce and specify products that can enhance color preference. The efforts made on color preference enhancement by adjusting light source spectral power distribution (SPD) can be traced to 1975, when the neodymium incandescent lamp was invented (Airola 1975; James 1984). In recent years, the adjustment of SPD is much easier for light emitting diode (LED) lighting products, which provides more opportunities to enhance color preference. On the other hand, researchers conducted psychophysical studies to further understand how human color preference varies with light source color rendition and tried to develop better measures to characterize color preference of light source for guiding manufacturers, specifiers, and designers (David et al. 2015; Houser et al. 2013).
A Vector Field Color Rendition Model for Characterizing Color Shifts and Metameric Mismatch
Published in LEUKOS, 2020
Aurelien David, Tony Esposito, Kevin Houser, Michael Royer, Kevin A. G. Smet, Lorne Whitehead
The color appearance of an object can shift when the spectral power distribution (SPD) of the illumination is altered, even if the chromaticity and illuminance are held constant. This phenomenon of light source–induced color shifts is an important concept underlying color perception research, which includes studies that range from the purely objective, such as spectral radiometry, to highly subjective issues of human well-being. Because there is some inconsistency in the use of some terms within the relevant literature, we present definitions for key terms that appear herein in Table 1.
Smart lighting systems: state-of-the-art and potential applications in warehouse order picking
Published in International Journal of Production Research, 2021
Marc Füchtenhans, Eric H. Grosse, Christoph H. Glock
In recent years, LEDs have advanced substantially, and they now offer more energy-efficient lighting and improved light control opportunities, such as shorter switching times, efficient dimming techniques, a broader spectral power distribution as well as a higher light intensity (Park, Lee, and Kim 2015; Wang and Linnartz 2017; Wang et al. 2012). LED-based lighting is the foundation of most current lighting systems and for several emerging technologies that cannot be realised without LEDs. The first crucial improvement of LEDs compared to traditional lighting systems (e.g. incandescent bulbs and fluorescent lamps) is their energy consumption. According to the literature, the luminous efficiency of LED luminaries is approximately 100 lm/W in home environments or street lighting and up to 200 lm/W in industrial environments, while incandescent bulbs have approx. 15 lm/W and fluorescent lamps approximately up to 100 lm/W (Chang et al. 2015). Other advantages include their long lifespan that ranges from 50,000 to over 100,000 h (Schratz et al. 2013; Vahl, Campos, and Filho 2013), their robustness and stability independent of the amount of shifting, and a high natural colour rendering with flicker-free light. Novel LED technologies can adjust both colour temperature and light intensity due to dimmable bicolour LED lamps (Lee et al. 2016; Cupkova et al. 2019). The heat radiation of traditional lighting systems does not exist for LEDs, so that coolants and lubricants combined with dust cannot burn in. This usually results in lower maintenance/replacement cost (Chew et al. 2017). An easy way to convert an existing lighting system to LED luminaires are so-called retrofit lamps that replace existing conventional luminaires with LEDs; the LEDs can also be adapted to customer-specific requirements while avoiding traditional technical standards (Dubois et al. 2015; Santamouris and Dascalaki 2002).