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What are these wave-like moving black areas shown in the following gif? Why do they start to appear when the exposure (or brightness) gets lower than a certain point? Why do the frequency and the length of these black areas change as the exposure changes?

Strange behavior of a light bulb

Please note that the light bulb itself has four separate filaments and the fixture globe has pointed areas which all can be considered as distinct light sources.

I appreciate you all.

Caspian Sea Seal
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  • So there is obviously something non-trivial going on there. My thoughts went something like: "PWM for diming? With different filiments connected across different arms of a rectifier?? In some kind of effort to get away with using too long a base period???" No idea if that's the right line of equiry, however. – dmckee --- ex-moderator kitten Sep 27 '19 at 22:34
  • This is a photography issue related to the way sensors read data and exposure values (including exposure time) are calculated by the camera as well as the frequency of the current producing the light. Suggest you check for an answer on Photography SE. – StephenG - Help Ukraine Sep 27 '19 at 22:51

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This is not an incandescent bulb. It's an LED bulb with strings of LEDs on wires arranged to look like incandescent filaments.

These LEDs are blinking too fast for the eye to see, but the camera's exposure is fast enough to record moments when one or the other "filament" is unlit, leading to the appearance of flashing as the LED flashing frequency beats with the camera's frame frequency.

There may also be an effect involved where different parts of the camera's image sensor aren't activated to capture light at the same instant. Instead, the active area of the sensor moves across the sensor during the exposure in a way that depends on the sensor and camera design. This can lead to bands of light and dark in an image taken with rapidly flashing light.

The Photon
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