Flicker: The Specification Nobody Puts on the Carton

Flicker is the most invisible specification in lighting. It does not appear in photographs, it does not prevent a product passing a basic functional test, and it produces complaints that are described as headaches rather than as flicker.

Two kinds of flicker

Visible flicker, where the eye perceives pulsing, usually from a driver with poor regulation or a dimmer interaction. Invisible flicker, where the light pulses at a frequency the eye cannot follow but the nervous system still responds to, most commonly reported as fatigue after a day at a desk.

Why cheap drivers flicker

Simplified driver circuits smooth the rectified mains incompletely, so the output carries a ripple at twice the line frequency. The cost saving is a few cents on the bill of materials and the visible symptom appears only at certain dim levels or on camera.

Where it becomes a commercial problem

Video calls, because cameras sample at a fixed rate and pick up beating that the eye ignores. Retail displays, where a phone camera is used constantly. Offices where the same people sit under the same light for eight hours and report headaches without ever mentioning the lamp.

How to test without a laboratory

Point a phone camera at the lamp at a low dim setting and look for horizontal bands. It is not a measurement, but it reliably detects the worst offenders, and it takes ten seconds at the sample stage.

What to ask for

Whether the driver is constant current, what the output ripple is at the lowest dim setting, and whether the driver is dimmable by design rather than made dimmable by the dimmer. The third question separates a real product from a hopeful one.