Regarding arousal, results revealed some of the measures to be
sensitive to screen luminance while other to ambient illuminance.
Although many studies have shown that exposure to lower levels
of light intensity can result in decreased alertness and performance
(see Section 1), none of them made a clear distinction between
screen luminance and ambient illuminance, nor explored their
conjoint effect on visual fatigue and arousal during digital reading.
Hence, the reason why some of the measures employed in our
experiment respond to luminance while other to illuminance
remains unknown.