PNNL

Abstract

“Flicker” has been recognized as an important consideration for lighting systems for over a century. More precise terms are temporal light modulation (TLM) as the stimulus, and responses to TLM to identify unwanted visual, cognitive, or physiological consequences. As electric lighting technology evolved, different forms of TLM emerged and so did responses to them. Today, LED systems—including the LED, driver, and control—can result in TLM that causes severe unwanted effects, while others may exhibit TLM producing no unwanted effects at all. An important factor is the modulation that results from the combination of the driver and the dimmer. The commonly used pulse width modulation (PWM) technique can introduce rectangular modulation with varying duty cycles and high Fourier frequency content, which can increase unwanted responses, especially among more sensitive individuals who are more likely to experience eyestrain, headaches, or migraines in their daily activities. This review focuses on the technology and research history that has led to current metrics for quantifying TLM and human responses to it. It examines evidence to provide a better understanding of applications where the stroboscopic and phantom array effects are found. Direct flicker effects at modulation frequencies less than about 80 Hz and the stroboscopic effect at modulation frequencies greater than 80 Hz are fairly well understood, but the phantom array effect still needs more exploration and characterization. Individuals with visual impairment may exhibit alterations in their response to TLM, but a discussion of this is beyond the intent of this review. Thus, examination of the effects of TLM will be directed towards individuals with normal visual function.