You see, artificial light sources can effectively change color with shutter speeds. It may sound crazy, but it’s true. Many types of artificial lights cycle, or flicker, at a rate much faster than our eyes can see, and fast camera shutter speeds can sometimes capture these cycles in pictures. This problem is particularly evident under fluorescent lights in office settings and under sodium-vapor lights commonly used in sports arenas and gymnasiums.
Back in the film days, it wasn’t the sort of thing that was seen very often because you typically couldn’t shoot at, say, 1/500th of a second in a dim office environment. But with the advent of low-noise capture at high ISOs came the ability to shoot at faster shutter speeds indoors.
I’ve encountered the problem at 1/250th and 1/500th shutter speeds, but it can happen at faster shutter speeds as well. The issue is the light cycling on and off—or flickering—at such a rate that it flickers off during a portion of the capture. Because slower shutter speeds expose the entire frame at once and allow for any flickering to effectively “blend” into the longer exposure, the problem is pretty much isolated to shutter speeds above 1/60th or 1/125th based on the rate at which the lights are cycling. At those shutter speeds, capturing an “off” cycle could result in a color shift, or an underexposure, or both. At 1/250th or faster, when the focal plane shutter never reveals the entire sensor at once, capturing the “off” cycle will translate into a band on the frame that’s underexposed and/or off-color. If you’ve encountered color banding when shooting at fast shutter speeds indoors, this is the likely culprit.
Take a look at one of the examples here, with the speaker in front of the LED-projected screen (lead image, top of the page). In reality, that screen displayed white light. But because of the cycling of the projector, we see red and blue bands. It’s this same phenomena that happens—albeit not quite so dramatically—when regular overhead lights cycle on and off.
So now that you’ve identified it, how do you fix it? Well, you could try to correct for the colorcast in post using a gradient adjustment to the color balance, but this is, frankly, difficult to do well. I’ve tried it, and it’s better than nothing, but your best bet is eliminating the problem in the first place. You can do this with a slower shutter speed, but that’s not especially helpful when you need to stop fast-moving action. In practice, you have two options, and only one of them is an immediate fix.
The first option is to crank the shutter speed as fast as you can and rattle off a burst of exposures in hopes of capturing the ideal frame without capturing an “off cycle.” The reality is, you’ll probably get a frame without color banding; hopefully, it’s the decisive moment, too. Not much of a guarantee, though.
The other option—the real fix—involves buying a new camera. Cameras such as the Canon EOS 7D Mark II, the Canon EOS-1D X Mark II and the Sony a99 Mark II feature anti-flicker settings that work very well to fight light-cycling color shifts. The method is surprisingly simple. The camera detects the rate at which the light source is cycling on and off ,and when you click the shutter-release button, the camera delays the actual shutter release for a tiny fraction of a second to allow it to synchronize with the light cycle. Pretty cool, huh? There’s the excuse you need to buy a new camera.