The effect of background illumination on sensitivity to intermittent photic stimulation

Sensitivity to intermittent photic stimulation (IPS) was tested in 23 photosensitive epileptic subjects under conditions of normal and reduced ambient lighting. Darkening the room to 20 lux did not increase either the incidence of photosensitivity or the effective range of flash frequencies. It is concluded that for routine clinical EEG examination there is no advantage in the current practice of darkening the room during IPS. For exhaustive testing of photosensitivity it is, however, necessary to perform IPS both in light and darkness.