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The effect of both temporal frequency and chromaticity on the visibility of the phantom array effect has been reported in literature. However, how the visibility changes with the temporal frequency is not consistently answered yet and, therefore, needs additional measurements. As for the effect of chromaticity, literature describes studies with different luminaires (i.e., with different chromaticities and peak wavelengths) and settings (i.e., different intensities and viewing geometry); as a consequence, it is challenging to compare these results directly. Therefore, we investigate the effect of temporal frequency on the visibility of the phantom array effect again, but with a special interest in how the peak frequency changes with chromaticity. The results of our experiment show a bandpass-shaped sensitivity function for the phantom array effect with a peak at 600 Hz, without significant change as a function of the chromaticities used in our experiment. However, the peak sensitivity value is found to be higher with red light than with green and white light.

As attention to indoor environmental quality (IEQ) grows, a systematic strategy for assessing IEQ in schools needs to be developed. For this purpose, this paper presents a summary of parameters measured in school classrooms to characterize the quality of thermal, acoustic, and visual environments and indoor air quality (IAQ). The summary is based on a review of published literature reporting measurements in schools in Europe and North America in the past ten years. It also summarizes the measurement protocols and measured concentrations. Eighty-eight papers describing measurements in schools were identified and analyzed. No unique standardized measuring method was used in the reviewed studies and different parameters were measured. The most often measured parameters were those describing the thermal environment and IAQ. The former mainly comprised air temperature and relative humidity. The latter mainly comprised concentrations of carbon dioxide, particulate matter, radon, formaldehyde, and some volatile organic compounds. The measured parameters describing acoustic and visual environments mainly comprised noise level, reverberation time, and illuminance. A few studies reported additional measurements of radiant temperature, operative temperature, and speech intelligibility. Measurement protocols from different studies show inconsistency in sampling duration and location and expressed results. Measured concentrations also show high variation between studies, with some pollutants exceeding the threshold values proposed by local and/or international organizations such as the World Health Organization (WHO). This review provides the reference for developing a rating scheme and protocols for uniform characterization of classroom IEQ.

The phantom array effect is the least studied temporal light artefact (TLA) among the three defined in TR 249:2022 by CIE Technical Committee 1-83 “Visual Aspects of Time-Modulated Lighting Systems.” Models that predict the visibility of both flicker and the stroboscopic effect have been detailed by the CIE and the IEC. When it comes to the phantom array effect, its visibility in real-life situations is most often described as ‘in an otherwise dark environment’, during ‘night driving conditions’, and from a ‘backlight of a car at night’. Thus, almost all laboratory investigations on the phantom array effect adopted experimental conditions with bright light sources in a dark room (i.e., < 1 lx). Multiple psychophysical investigations have studied the phenomenon qualitatively or quantitatively. Variables that have been employed in these studies can be categorized as: 1) individually related characteristics: the age and gender of the observer, and maybe also the saccade speed (i.e., variations around the average speed determined by the size of the saccade amplitude); 2) characteristics of the light modulation: the time-averaged luminance/illuminance for direct/indirect viewing conditions, the temporal frequency, the modulation depth, the shape of the waveform, the duty cycle, and the chromaticity of the light source; and 3) characteristics of the viewing geometry: foveal or peripheral observance, the size of the light source (i.e., the subtended visual angle), the spatial distribution of the light source (i.e., with sharp or smooth edges), the saccade amplitude (which usually is fixed in an experimental setting), and the relative motion of the light source to the observer. Some of these studies measured the visibility of the phantom array effect, but others asked the observers to rate the noticeability and/or annoyance of the phantom array effect. The results of all these investigations can be summarized as follows. The visibility of the artefact did not dep