flicker

Flicker is the rapid variation in a light source’s brightness, and sometimes its color, that can be perceived by the human eye or detected by instruments. It is commonly discussed in the contexts of artificial lighting, display technology, and photography, where periodic modulation of light output is involved. Flicker can be visible or invisible depending on the frequency and the contrast with the surrounding environment.

In electrical lighting, flicker most often arises from the mains power waveform or from dimming methods such as pulse-width modulation (PWM) used to control LED brightness. Fluorescent and other discharge lamps can flicker due to ballast operation or aging components. Displays may exhibit flicker if backlights or image updates are not synchronized with the viewing device, and cameras can capture flicker as banding when a rolling shutter interacts with a flickering light source.

Perception and health effects vary with frequency and brightness. Flicker tends to be noticeable at lower frequencies, often below around 60 Hz, and high-contrast scenes can make it more evident. Some individuals experience headaches, eye strain, or migraines from flickering light, and photosensitive epilepsy can be triggered by certain flicker patterns, particularly within specific frequency ranges. High-frequency flicker is less perceptible but can still cause discomfort for sensitive viewers.

Measurement and standards exist to quantify flicker and to limit its presence in lighting and electrical equipment. Common metrics include flicker percentage or flicker index, and specialized instruments are used to assess performance. Mitigation strategies include increasing modulation frequency beyond perceptual thresholds, using constant-current drivers, improving power quality, and selecting lighting technologies designed for stable output. In photography and video, synchronizing frame rate and shutter speed with lighting helps minimize artifacts.