Dependence of Temporal Frequency and Chromaticity on the Visibility of the Phantom Array Effect

Abstract

Multiple studies have measured the visibility of the phantom array effect as a function of variables, such as temporal frequency, luminance/illuminance, size of the light source, saccade speed of the observers, and colour of the light. The effect of temporal frequency on the visibility of the phantom array effect is not surprising, since the human visual system is sensitive to spatial and temporal frequency of light. However, how the visibility of the phantom array effect changes with the temporal frequency is still not consistently answered in literature, and therefore, needs additional measurements. A provisional model of the visibility of the phantom array effect for a point light source based on the spatial contrast sensitivity function was described in CIE 249:2022; it predicted a sensitivity peak of around 1000 Hz. Some experimental investigations, however, showed a peak at about 600 Hz, while others concluded that the visibility decreased as the temporal frequency increased, and that the phantom array effect was even visible at very high frequencies of above 15 kHz. Since for the design of visually safe light sources it is crucial to understand when the phantom array effect becomes visible, we performed new measurements on its frequency dependency.Both spatial and temporal contrast sensitivity functions are colour-dependent, thus the effect of colour on the visibility of the phantom array effect is expected. This colour dependency has been reported in multiple studies. Since in these studies, different luminaires (i.e., with different chromaticities and peak wavelengths) and settings (i.e., different intensities and viewing geometry) were used, it is challenging to compare the results directly. Hence, to understand the effect of colour on the visibility of the phantom array effect also, additional measurements are needed.In summary, our motivation is to investigate the effect of temporal frequency on the visibility of the phantom array effect, with a special interest in where the peak is and how the peak frequency changes with chromaticity. Our dataset, together with other available data in the literature, can be used to model the sensitivity function of the phantom array effect in the future