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Canon EOS Crop Sensor for HD
APS-C sensor cameras including the 80D, 70D, 7D Mk. II, 7D, EOS M and Rebel models for HD video recording.


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Old June 21st, 2016, 10:31 AM   #1
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Banding with LED lights

Hello,

The other day I shot an interview in an office with two Canon 60D's and three LED lights. When I later looked at the footage, I saw that one of the cameras had horizontal banding, and the other didn't (with horizontal banding I refer to darker or lighter horizontal areas, "bands", continually floating up or down the image).

This was shot in a 60Hz electricity setting and the camera that had the banding shot at 1/50, the shutter speed I almost always use. The camera that did NOT have banding, was shooting at 1/40, because I needed to lighten it up a bit and there were not many movements in the image that would reveal a slower shutter speed.

As light sources I had only my three portable LED lights (two FotoDiox and one Genaray), I believe they were set to 3200 K, and I also kept some of the ceiling lighting turned on, BUT these were not fluorescent lights, they were LED too (those small office led yellow lights) and they did not make much of a difference, I used them only to raise the general level a bit. (I had turned off all fluorescent light)

So I am surprised I got banding using only LED lighting? Is that possible and what causes it? Is the solution to shoot at a slower shutter speed? Can other things affect the banding, for example the dimmer of the LED lights?

Both cameras were set to 29.97 fps and the banding camera had aperture 1.8 and iso 100.

Thank you for any suggestions or words of wisdom. :)
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Old June 21st, 2016, 04:57 PM   #2
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Re: Banding with LED lights

As LEDs are cool devices, they light up and go dark extremely quickly, quickly enough to be used for TV displays - Some are also very bright and use pulse wave dimming, so are constantly going on and off in sympathy with the mains frequency, and the PWM dimming. Some LEDs don't run flat out, and have a degree of dimming - so they are flickering. If the camera runs at a frame rate that matches the mains frequency, flickering is much, much less common - but with a camera set to 50 fps or 25 fps shooting in 60Hz mains locations, at some point the camera sensor is active at the the time the LED is out!, then gradually the ons and offs catch up with each other and it's bright, then the cycle starts again.

60Hz mains means 30(29.97) or double that for flicker free use with LED lighting.
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Old June 21st, 2016, 07:21 PM   #3
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Re: Banding with LED lights

Thank you for enlightening the subject :) So you say frame rate, not shutter speed, is the issue? Notice though, I was using frame rate 29.97 (30) fps in both cameras at 60 Hz frequency. What differed in the cameras was the shutter speed, and one got banding and the other not.
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Old June 21st, 2016, 10:25 PM   #4
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Re: Banding with LED lights

Shoot at 1/60 or 1/120 in 60 Hz regions. Lamps light on both the positive and negative swings, so they flash at 120Hz.
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Old June 22nd, 2016, 10:11 AM   #5
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Re: Banding with LED lights

Frame rate and shutter speed are linked. The number of frames per second is fairly straight forward but shutter speed is how long each frame is 'collecting' light. 25 frames a second could have each frame active for far less time. If you have a 25fps framerate set then only exposing each one for a smaller time increases the risk that at the time it's open for light collection, the LED source could be off. Bands that move up or down the screen are when the mains frequency and the camera frame rate are not exactly the same, so the band of brightest image tends to be moving. If the frame rate and mains are the same rate, the image can be pretty stable (by luck), or very dark (also by luck). As the shutter speed increases, the band tends to get narrower.
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Old June 22nd, 2016, 11:14 PM   #6
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Re: Banding with LED lig

The thing about collecting light is appropriate. At 1/60 you will collect it for two full cycles. At 1/120, you get one cycle. The frame rate changes the phase. Maybe you open the shutter when there is full light or no light but if you get an integral number of cycles, the phase is moot.
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Old November 8th, 2016, 01:53 PM   #7
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Re: Banding with LED lights

The 7D Mark II actually can detect flicker and compensate for it. I discovered this while shooting some soccer games underneath the lights. Of course then I got around to reading the manual and discovered the feature.
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