Why do photos shot with the same manual settings under continuous light shift between warm and cool color?
Asked 7/3/2020
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2 answers
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I shot a product sequence on a tripod using the same manual settings for every frame, but some images look warm/yellow and others cool/blue. In a few shots, part of the frame even looks warmer or cooler than the rest.
Setup:
- 2 continuous-light softboxes
- Camera in manual exposure mode
- 50mm, f/5.6, 1/320s
- White balance fixed at 5260K
- Spot metering
- RAW capture
Nothing in the setup moved between shots. Could spot metering cause this, or is there another reason for color shifts like this under continuous lighting?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
6y ago
2 Answers
4
Your LED lights are likely using pulse width modulation (do you have dimmers on them?). White LEDs attain their light using a fluorescence effect that creates yellow light via fluorescence from the LED's "native" blue light. When the LED is driven with pulsed current, the blue light will change faster than the yellow light follows, particularly on the on-off transition.
The other possibility is that room lighting, like fluorescent light bulbs, adds pulsed light with a different color balance.
Of course the elephant in the room would be if you have a setup with adjustable colors where separate dimmers using pulse width modulation are on different-colored LEDs.
Originally by user92899. Source · Licensed CC BY-SA 4.0
user92899
6y ago
0
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Spot metering is not the cause here if your exposure and white balance were fixed manually.
The most likely issue is flicker from your continuous lights, especially LED lights using pulse-width modulation (common when dimmed). LEDs can vary in both brightness and color during each pulse cycle, so at a fast shutter speed like 1/320s your camera may catch different parts of that cycle from frame to frame. That can make one image look warmer, another cooler, and can even cause mixed color across a frame.
Another possibility is other room lighting contaminating the scene, especially fluorescent or other flickering lights with a different color balance.
What to do:
- Turn off other ambient/room lights.
- If your softboxes are LED and dimmable, try full power instead of dimmed power.
- Use a slower shutter speed so each exposure averages more of the light cycle.
- If possible, use flicker-free lights designed for photography/video.
Since you shot RAW, you can correct the images, but preventing the flicker source will save a lot of work.
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