No abstract

A preliminary usefulness metric is defined. The metric is intended to characterize the energy efficiency of light sources in a more comprehensive way than the luminous efficacy of a source by taking selected spectral aspects of human centric lighting into consideration. The presented version of the metric is a combination of well-established measures of color quality, brightness and the circadian effect derived from the spectral power distribution of the light source. The metric includes a limited application dependence: it yields different values for interior and exterior applications, static and dynamic as well as relaxing and activating light source spectra. Light source categories (A-G) with preliminary category limits were also computed in the two-dimensional diagram associated with the metric. The metric should be considered as a basis for further discussions and not as a final solution.

In 1931, the CIE published and standardised the photopic luminous efficiency function. Based on these standardized curves,luminous flux in lumens, luminance in cd/m2, and illuminance in lux are determined by an integral of these curves and theincident light spectra in photometers and are considered as a physical brightness. However, human brightness perception isnot only weighted by this simple determination, but is a more complicated combination of all L-cones, M-cones, S-cones, rods,and later ipRGCs, which was partly illustrated by the equivalent brightness of Fotios et al. with the correction factor (S/V)0.24.Recently, new researches have mentioned the role of ipRGCs in the human brightness perception. However, it is still unclearhow these signal components of the human visual system are involved in overall human brightness perception. In this work, thehuman brightness perception under photopic conditions was studied by experimenting with 28 subjects under 25 different lightspectra. These spectra were varied not only in brightness but also in spectral geometry. In this way, the contributions of thesignal components can be investigated. Subsequently, an optimization process was performed with the obtained database. Theresults show that not only the photopic component, but also the S-cones and ipRGC play their role, although it is smaller. Thus,the visually scaled brightness model based on the database optimization was constructed with not only illuminance but alsoS-cones and ipRGC with R2 of 0.9554 and RMSE of 4.7802. These results are much better than the Fotios-based brightnessmodel with only S-cones (R2 = 0.8161, RMSE = 9.7123) and the traditional model without S-cones and ipRGC (R2 = 0.8121,RMSE = 9.8171). It also suggests that a "blue-sensitive" signal (S or G=ipRGC or their combination) should be given seriousenough attention in the human brightness perception, and a more comprehensive study is needed to investigate it more deeply.

The circadian stimulus is an important, validated and updated metric that describes the invisible influences of light on the human circadian system explicitly and scientifically. However, an absolute spectral power distribution must be supplied for its computation, which is only measurable by an expensive and complicated spectrometer. This paper proposes an alternative circadian stimulus computation model that is identified as the function CS(z, Ev) for white light sources based on the most common and simplest parameters of illuminance Ev in lux and the chromaticity coordinate z. These parameters are well known and widely used in both colour science and lighting technology. In order to prove the accuracy and availability of the model, an internal validation was performed with the adapted method repeating split data to check the goodness of the model fit. The fitted model achieved a maximum residual of 0.058 in the circadian stimulus quantity (R2 = 0.998). An external validation with the maximum residual of 0.030 (R2 = 0.999) provided stronger evidence for the usability of the model in applications.

No abstract

Smart integrative lighting systems aim to support human health and wellbeing by capitalising on the light-induced effects on circadian rhythms, sleep, and cognitive functions, while optimising the light’s visual aspects like colour fidelity, visual comfort, visual preference, and visibility. Metameric spectral tuning could be an instrument to solve potential conflicts between the visual preferences of users with respect to illuminance and chromaticity and the circadian consequences of the light exposure, as metamers can selectively modulate melanopsin-based photoreception without affecting visual properties such as chromaticity or illuminance. This work uses a 6-, 8- and 11-channel LED luminaire with fixed illuminance of 250 lx to systematically investigate the metameric tuning range in melanopic equivalent daylight illuminance (EDI) and melanopic daylight efficacy ratio (melanopic DER) for 561 chromaticity coordinates as optimisation targets (2700 K to 7443 K ± Duv 0 to 0.048), while applying colour fidelity index Rf criteria from the TM-30-20 Annex E recommendations (i.e. Rf$$\ge$$ ≥ 85, Rf,h1$$\ge$$ ≥ 85). Our results reveal that the melanopic tuning range increases with rising CCT to a maximum tuning range in melanopic DER of 0.24 (CCT: 6702 K, Duv: 0.003), 0.29 (CCT: 7443 K, Duv: 0) and 0.30 (CCT: 6702, Duv: 0.006), depending on the luminaire’s channel number of 6, 8 or 11, respectively. This allows to vary the melanopic EDI from 212.5–227.5 lx up to 275–300 lx without changes in the photopic illuminance (250 lx) or chromaticity ($$\Delta u'v'$$ Δ u ′ v ′ $$\le$$ ≤ 0.0014). The highest metameric melanopic Michelson contrast for the 6-, 8- and 11-channel luminaire is 0.16, 0.18 and 0.18, which is accomplished at a CCT of 3017 K (Duv: − 0.018), 3456 K (Duv: 0.009) and 3456 K (Duv: 0.009), respectively. By optimising ~ 490,000 multi-channel LED spectra, we identified chromaticity regions in the CIExy colour space that are of particular interest to control the melanopic efficacy with metameric spectral tuning.

No abstract

No abstract