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Radiometry, Photometry, and Radiation Heat Transfer
Published in Julio Chaves, Introduction to Nonimaging Optics, 2017
We may now define the luminosity function V(λ) (or photopic luminous efficiency function) the same way as the luminous efficacy, but normalized to its maximum value of 683, which occurs at 555 nm. We then have V(555) = 1. The luminous efficacy function can then be given by 683V(λ) where V(λ) is the luminosity function.2 Note that V(λ) is dimensionless, but is multiplied by 683 lm/W to give the luminous efficacy.
An underwater lighting and turbidity image repository for analysing the performance of image-based non-destructive techniques
Published in Structure and Infrastructure Engineering, 2018
Michael O’Byrne, Franck Schoefs, Vikram Pakrashi, Bidisha Ghosh
Lighting also plays a pivotal role for achieving good visibility. Ambient light may be sufficient for near-surface inspections; however, it is unlikely to be sufficient at greater depths at which point artificial light will become necessary. Three light levels were used: 100 lux, 1000 lux, 10,000 lux. To put this in perspective, the approximate level of light, or illuminance, on a very dark overcast day is 100 lux, a moderately overcast day is 1000 lux, and full daylight (not direct sunlight) is 10,000–25,000 lux (Schlyter, 2009). The lux is the SI unit of illuminance that measures the intensity of light that strikes a surface, as perceived by the human eye. It is similar to irradiance, which has units of watts per square metre, but with the power at each wavelength weighted according to a standardised luminosity function that is based on a model of human visual brightness perception. The illuminance can be measured using a lux meter, which are readily available and portable. A specimen from each section of the repository is shown under varying lighting and turbidity levels in Figures 5–7.
Coming to Light: Principles for Successful Lighting Design of Footbridges
Published in Structural Engineering International, 2018
The luminous flux Φtotal, expressed in lumen (lm), specifies the total quantity of light emitted by a light source based on the luminosity function, a standardized model of the sensitivity of the human eye V(λ). The luminosity efficiency is the ratio of luminous flux to electrical power consumed (lm/W), which provides information about the economic efficiency of any artificial light source.
Photoreceptor Enhanced Light Therapy (PELT): A Framework for Implementing BiologicallyDirected Integrative Lighting
Published in LEUKOS, 2023
Beatrix Feigl, Drew D. Carter, Andrew J. Zele
We specified the PrD lights with reference to the excitations of all five photoreceptor classes (Zele et al. 2019) using the CIE 1964 10° Standard Observer cone fundamentals (Smith and Pokorny 1975), the CIE 1951 scotopic luminosity function, and the melanopsin spectral sensitivity function (Adhikari et al. 2015; Enezi et al. 2011). Retinal illumination (photopic) was defined as the sum of L- and M-cone excitations with a 2:1 L:M cone ratio (MacLeod and Boynton 1979), such that for a white-appearing equal energy spectrum at 1 photopic Troland (Td), the photoreceptor excitation relative to photopic illumination is 0.6667 for L-cones (L), 0.3333 for M-cones (M), 1 for S-cones (S), 1 for rods (R), and 1 for melanopsin (i). We applied a luminance-normalization, wherein each photoreceptor excitation for a given light spectrum was divided by the photopic luminance (Vλ) of that spectrum. In the following analyses, the spectral distributions of natural daylights were referenced to the Illuminating Engineering Society (IES) TM-30 standard which uses a combination of CIE D-series illuminants and functions calculated using Planck’s radiation law. The spectral distributions of the natural daylights were correlated with the photoreceptor sensitivity functions to give five SMLRi values per natural daylight spectrum (Table 1). Each SMLRi group was then divided by the sum of its individual L and M components so that the L + M of each SMLRi equals 1. The SMLRi values are equivalent to the CIE S026/E:2018 α-opic efficacy of luminous radiation (ELR). Our data are based on scaling the photoreceptor spectral sensitivity functions relative to an equal energy spectrum before correlating with the luminance-normalized spectra, whereas CIE S026/E:2018 uses unit-normalized photoreceptor spectral sensitivity functions, correlates with a luminance-normalized spectra and then references to the D65 illuminant ELR. The Daylight Efficacy Ratio (DER) can be calculated from the SMLRi values (Table 1) by dividing the test SMLRi by a reference SMLRi (e.g., at 6500 K, D65). Equivalent daylight illuminance (EDI) can be determined from DER and absolute illuminance measurements.