Interference between Foveal and Peripheral Visual Tasks, Potentially Affecting Mesopic Photometry

Commission Intemationale de l'Eclairage (CIE) published CIE 191: Recommended System for Mesopic Photometry Based on Visual Performance was published in 2010. However, it is still necessary to identify appropriate applications and make guidelines for the new mesopic photometry system. To this end, we dealt with interference between the foveal task and the peripheral task that often exists in the real driving context. Such interference often appears to exaggerate the effectiveness of short-wavelength radiation on peripheral visual performance at mesopic light levels. To address a question of how the foveal vision affects the peripheral vision for different spectral power distributions, but for the same mesopic luminance, we conducted a controlled laboratory experiment and two supplemental laboratory experiments. In these experiments, we asked subjects to perform a foveal tracking task and a peripheral target-detection task, simulating nighttime multi-tasking driving activities in mesopic light levels. Based on the results of the experiments we confirmed the Purkinje phenomena. We also found interference between the foveal task and the peripheral task (especially when the foveal task was difficult). Such interference not only impairs the foveal task performance but also reduces the peripheral responses significantly, and potentially makes the Purkinje phenomena appear to be exaggerated. This confirmed the importance of using light sources with more short-wavelength radiation for better peripheral visibility in nighttime roadway lighting applications. Such interference also suggests that the use of a simple easy task may help eliminate any effect of interference on databases to establish a unified mesopic photometry system.