Psycho-perceptual Effects of Different Approaches to E-Flares

Optical Response
The human eye and brain respond differently to various light sources. Flashing or moving lights are more attention getting than fixed or stationary lights as the brain processes the movement as a possible alarm situation. Research has shown that flash rates of 2 to 7 per second are the most effective at alerting the viewer.

Duration
The duration of the flash can affect the binocular response of the viewer. If the duration of the flash is too short the brain can tell that there is a light source but cannot form a judgement of distance. Flash durations of less than a few milliseconds will disable the binocular capability of the brain. It is often very difficult to judge the distance of a Strobe source. Indeed strobes are often pulsed two or three times per cycle to try to overcome this problem.

Apparent Brightness
The apparent brightness is affected by the ratio of light-on to light-off periods. The optimum is an on to off ratio (duty cycle) of between 1 to 3 and 1 to 5.

Contrast Ratio
The difference between the brightness of the light and the background (the contrast ratio) is also important being high enough to get attention and not to high that the eye is saturated.
The intensity of the very short duration pulses emitted by a strobe can affect the night vision of pilots and other dark adapted viewers to such a point their night vision may be affected for a few minutes if there is a strobe light in their vicinity.