Effect of luminance level on electro-encephalogram alpha-wave synchronisation

A control system for the remote activation of electronic devices, based on alpha-wave synchronisation, must be robust over a wide range of lighting conditions. This study investigates the effect that low light levels have on the increase in amplitude of the occipital alpha-wave component of the human electro-encephalogram spectrum in response to eye closure. Measurements of the time required for the amplitude of the occipital alpha wave to increase above a predetermined threshold, upon eye closure, were taken from 21 subjects and at four illuminances, ranging from 2 × 10^-1 lx to 2 × 10^-5 lx. The light source used to provide these illuminances was a featureless, uniformly illuminated white paper that subtended 30° of the visual field. Statistical analysis showed that the time to exceed threshold (TTET) upon eye closure was not independent (p<0.001) of illuminance, and that the main source of this lack of independence occurred at the lowest illuminance, 2 × 10^-5 lx. At this luminance, the median TTET value was 15.0s. However, at 2 × 10^-4 lx, the median value of the TTET was 4.2 s. This is a sufficiently short time for device activation, and therefore a control system based on alpha-wave synchronisation is functional at very low light levels.