why do cameras flicker

The Deep Dive

The flicker phenomenon is fundamentally a dance between two frequencies: the electrical grid's alternating current and the camera's sensor sampling rate. In most regions, AC power oscillates at 50 or 60 Hertz (Hz), causing incandescent and fluorescent bulbs to dim and brighten 100 or 120 times per second, though our eyes perceive this as a steady glow due to persistence of vision. A camera's sensor, however, captures discrete frames. When its shutter speed is set to a value that is not a precise multiple of the light's flicker cycle, it will sample the light at different points in its brightness oscillation. For example, if one frame captures the light at its peak intensity and the next captures it as it's dimming, the resulting footage will show a noticeable pulse. This is exacerbated by rolling shutter sensors, which read the image line-by-line, potentially capturing different flicker phases across a single frame. Modern solutions include flicker reduction settings that synchronize the shutter timing with the electrical frequency, or using direct current (DC) powered lights like many LEDs, which provide a constant output.

Why It Matters

Understanding camera flicker is crucial for professional videography, broadcasting, and security monitoring. Uncontrolled flicker can ruin footage, making interviews, sports events, or surveillance recordings unusable. This knowledge informs lighting choices on film sets and guides the development of flicker-free LED technology for studios. For consumers, it explains smartphone video quirks and empowers them to adjust settings for better results. Ultimately, it bridges the gap between how we perceive light and how machines capture it.

Common Misconceptions

A common myth is that flicker is always a sign of a faulty or low-quality camera. In reality, even high-end cinema cameras will flicker if their shutter speed is incompatible with the light source's frequency. Another misconception is that flicker only occurs under fluorescent lights. While fluorescent tubes are notorious, any AC-powered light, including many household LEDs and incandescent bulbs, can cause it if the camera settings are mismatched. The issue is one of synchronization, not light type alone.

Fun Facts

• The first motion picture projectors used an arc lamp and a manually cranked shutter, creating a flicker rate so low it was often called 'the flicks.'
• Some high-end smartphone cameras now use a global shutter sensor that reads the entire image simultaneously, which can eliminate rolling shutter artifacts and mitigate certain types of flicker.