The eye drives non-visual (NV) responses to light, including circadian resetting, pupillary reflex and alerting effects. Initially thought to depend on melanopsin-expressing retinal ganglion cells (ipRGCs), classical photopigments play a modulatory role in some of these responses. As most studies have investigated only a limited number of NV functions, generally under conditions of relatively high light levels and long duration of exposure, whether NV functions share similar irradiance sensitivities and response dynamics during light exposure is unknown. We addressed this issue using light exposure paradigms spectrally and spatially tuned to target mainly cones or ipRGCs, and by measuring longitudinally (50 min) several NV responses in 28 men. We demonstrate that the response dynamics of NV functions are faster than previously thought. We find that the brain, the heart, and thermoregulation are activated within 1 to 5 min of light exposure. Further, we show that NV functions do not share the same response sensitivities. While the half-maximum response is only ∼48 s for the tonic pupil diameter, it is ∼12 min for EEG gamma activity. Most NV responses seem to be saturated by low light levels, as low as 90 melanopic lux. Our results also reveal that it is possible to maintain optimal visual performance while modulating NV responses. Our findings have real-life implications. On one hand, light therapy paradigms should be re-evaluated with lower intensities and shorter durations, with the potential of improving patients’ compliance. On the other hand, the significant impact of low intensity and short duration light exposures on NV physiology should make us reconsider the potential health consequences of light exposure before bedtime, in particular on sleep and circadian physiology.

General lighting is undergoing a revolutionary change towards LED-based technologies. To provide firm scientific basis for the related colorimetric and photometric measurements, this paper presents the development of new white-LED-based illuminants for colorimetry, and their evaluation to recommend a new reference spectrum for calibration of photometers. Spectra of 1516 LED products were measured and used to calculate eight representative spectral power distributions for LED sources of different correlated colour temperature categories. The suitability of the calculated representative spectra for photometer calibration was studied by comparing average spectral mismatch errors with CIE Standard Illuminant A, which has been used for decades as the reference spectrum for incandescent standard lamps in calibration of photometers. It was found that in general, when compared with Standard Illuminant A, all the potential LED calibration spectra reduced spectral mismatch errors when measuring LED products. Out of the potential LED calibration spectra tested, the white LED spectrum with correlated colour temperature of 4103 K was found to be the most suitable candidate to complement Standard Illuminant A in luminous responsivity calibrations of photometers. When compared with Standard Illuminant A, employing the 4103 K reference spectrum reduced the spectral mismatch errors, on average, by approximately a factor of two in measurements of LED products and lighting. Furthermore, the new LED reference spectrum was found to reduce the spectral mismatch errors in measurements of daylight, and many types of fluorescent and discharge lamps, indicating that the proposed reference spectrum is a viable alternative to Standard Illuminant A for calibration of photometers.

The CIE General Color Rendering Index Ra is currently widely and internationally used to assess the ability of white light sources to render colors. But over the past decades, there has been increasing evidence of its limitations. As a result of several years of scientific work, the Commission Internationale de l'Eclairage (CIE) published in April 2017 an updated calculation method. To reduce misinterpretation by users and make a clear distinction with the other aspects of color quality, the color rendering index was renamed color fidelity index (CIE-Rf). Before proposing this index as a new international standard for color fidelity prediction, there is a need for validation. This paper presents a psychophysical experiment designed to address this aim. Twelve observers evaluated color differences of 16 color samples under eight pairs of light sources. 3000K and 4000K light-emitting diodes and fluorescent sources with CIE-Rf values ranging from 64 to 94 were investigated. Results show that the prediction of color differences is significantly better in CAM02-UCS color space than in CIE UVW or CIELAB, whatever the color matching functions. A high correlation was found between perceived color differences and CIE-Rf. This psychophysical experiment did not make it possible to detect significant differences with the other tested color fidelity indices (CIE-Ra, CQS-Qf, CRI2012, CRI-CAM02UCS, and IES-Rf). However, there are some signs of an improvement of the prediction by CIE-Rf in comparison to CIE-Ra. To increase, in further works, the chance to detect potential significant differences between color fidelity indices, some modifications of the experimental protocols are suggested.