Checking LED PWM Illumination Against Camera Exposure Timing

An LED source that looks steady to a person can produce bands or inconsistent brightness in camera images. The sensor integrates light during particular exposure intervals, which may capture different portions of the PWM waveform. Analyze the optical timing and camera shutter method together before blaming image processing.

Identify the camera exposure sequence

Determine whether the sensor uses a global or rolling shutter and obtain the timing relevant to the selected mode. The Basler documentation on electronic shutter types explains the distinction between simultaneous and sequential row exposure. The camera’s frame rate alone does not describe those exposure intervals.

Record exposure duration, row timing where applicable, region of interest, frame rate, and any synchronization output. Automatic exposure changes should be disabled or recorded during a controlled investigation.

Measure the actual light waveform

Use a suitable photodetector to observe light intensity versus time. Compare it with the LED control signal and camera timing. Electrical PWM at the driver input may not match optical output because of decoding, current dynamics, or an internal modulation scheme.

A hypothetical 1 kHz light pulse train has a 1 ms period. A 100 microsecond exposure samples only part of that period, so its result can depend strongly on phase. This example illustrates timing sensitivity; it does not establish a universal frequency at which every camera becomes insensitive.

Test phase and operating changes

Capture images over many relative phases rather than selecting one favorable frame. Sweep the relevant brightness settings and exposure times. With a rolling shutter, compare the location and movement of bands as timing changes.

Include the actual image region and readout mode. A change that modifies row timing can alter the observed pattern even if the lighting waveform and nominal frame rate remain unchanged.

Evaluate a suitable correction

Consider supported synchronization, continuous illumination during exposure, a different modulation frequency, or another dimming method according to the system requirements. Check optical power, thermal limits, and motion blur consequences alongside image uniformity.

Save camera mode, exposure settings, light waveform, synchronization arrangement, and a representative sequence of images. Define acceptance over the intended operating range, including the shortest exposure and lowest brightness that matter. A stable looking lamp or one clean photograph does not establish camera compatibility. The useful result demonstrates that the sensor receives sufficiently consistent integrated light during every relevant exposure interval, with the actual driver and camera settings used in the product. Record the actual camera firmware and driver operating modes.