Pulse width modulated LED light control and vision adaptation

Abstract

In view of the fact that excessive illumination levels are economically and hygienically unprofitable, it is necessary to use LED lights with adjustable brightness. As LEDs are DC devices, a pulse width modulation (PWM) may be effectively used; it enables variations of LEDs current and luminous characteristics within a wide range. The method of brightness control with PWM for LED sources featuring a moderate inertia generates an enormous pulsation of luminous flux imperceptible to humans but adversely affecting human health. Given a low inertia of LED sources becomes evident, inertial properties of human vision must be considered. When designing a safe lighting system, processes of fast and slow adaptation at perception of flickering light should be taken into account. For that purpose, a mathematical model complying with basic laws of physiological optics and reflecting vision perception of flashing light was developed. Estimate of vision inertial properties proved the need for increase of PWM frequency at luminous flux control.