A frequent question I receive from photographers is "Why are some of my pictures dark and some bright even though I used the same camera settings – the same shutter speed, the same aperture and the same ISO setting – under constant light levels?" Most encountering this problem are very concerned that their camera has a problem – perhaps with the shutter. Fortunately, the camera is not usually the problem. Unfortunately, the resolution of the problem is not as easy as sending the camera in for repair.
The problem images generating the question have usually been captured under fluorescent or gym/arena lighting and a short exposure was often used. Shooting action sports with a fast frame rate is most frequently the source – most of these images will appear properly exposed but an intermittent dark image glaringly appears.
The cause of this problem is usually not the camera, but the light themselves. While those lights may appear to be very constant (and they may indeed be above the flicker fusion threshold/rate where intermittent light appears constant to us), they may not be so. While some lights exhibit very little flicker, some lights are far more intermittent in their output than others. The more intermittent the light output, the more likely that your very short exposure may be timed to coincide with that light's low cycle. And the result is a dark image.
The sun is 100% flicker-free and some light types including tungsten and electronic ballast fluorescent approach this performance. But put a magnetic ballast behind a gas discharge-type lamp and you can prepare for intermittent lighting issues. If your exposure time is long, you might not notice the drop in lighting as much (you may capture an entire illumination cycle or multiple cycles). But when shooting at fast shutter speeds under the flickering lights commonly found in indoor and outdoor sports venues, every shot is a bit of a surprise.
Let me share some light flicker photography examples:
All images in each of the three sets above were taken from consecutive frames in 12 fps bursts from a Canon EOS 1D X with a Canon EF 200mm f/2 L IS USM Lens mounted. The exposure/brightness settings were locked in at f/2 and 1/500. ISO was set at 3200 for the first example and 5000 for the second two. No post-processing changes aside from the Standard Picture Style being selected and sharpness reduced to "1" were applied to these images.
Obviously, the images within each set have vast differences in brightness AND white balance. Even the exit sign goes from bright to dark. This is the point when many photographers begin asking "Is something wrong with my camera?" and "Why is my camera giving me dark images?"
The cause once again is flickering lights. I believe from metal halide magnetic ballast lights in this case.
What do you do about the flickering lights problem?
One option is to get the venue's lighting upgraded. There are light sources with much less flicker problems available. In fact, the venue the example images were captured in has two indoor fields. The electronic ballast fluorescent lighting used in the constructed-later second field has no flicker issues from my camera's perspective. Replacing a venue's lighting is a bit extreme and not a viable option for most of us.
A great option is to strobe the venue. Securely mount high-powered strobe lights in the venue's ceiling and fire them remotely with PocketWizards. This lighting technique promises the best-possible full-spectrum lighting. The downside is that doing this is somewhat costly, is moderately time-consuming and requires access to the venue's ceiling area (and permission for flash-photography use). If you are shooting many events in the same venue, this strategy might be worth persuing. For example, if you are shooting all of a university's basketball games for a season, the ideal lighting may be worth the effort and cost required to strobe the arena.
Strobing an outdoor venue is not as frequently done.
The next-step-down bring-your-own-light option is to use an accessory hot-shoe-mounted flash (if permitted). Unfortunately, overpowering the existing lighting at larger venues is tough and the look of direct flash is not ideal. Still, we are talking about improving upon lights that are producing far-from-ideal light in the first place. So, the flash may be the better option.
If opting to use a hot shoe flash, consider using a color correction gel to balance your flash color balance to that most frequently being produced by the existing lights. Max flash sync shutter speeds may not be fast enough if you are not overpowering the ambient lighting. And flash power is reduced if using high speed flash sync.
The option that many (most?) take is to simply deal with the conditions. Shoot in RAW and select an exposure that does not result in blown highlights when the lights are under full output. Shoot a short burst to insure that you have captured a bright frame to check your exposure with. Adjust the brightness of the resulting images as desired during post processing. This of course means adding a significant amount of brightness to the lights-off shots. And since you are likely already using high ISO settings, these images are not going to have great quality. Shoot more images than you need so that you feel more comfortable deleting the poor quality ones.
Adjusting white balance is the other important post-processing step needed for correcting images captured under flickering lights. Your white balance will likely vary greatly from shot-to-shot as it does in my examples above. The best practice here may be to get your primary subject to wear something neutral-colored – perhaps a hair band or wristband. Use that item for your custom white balance adjustment for every shot. Otherwise, hopefully something in your image backgrounds is neutral colored to make proper white balance aquisition easy.
Staged photos often lack something that real game action photos deliver, but when the lighting conditions are terrible, you might want to consider adding some staged shots into your mix. Find out when the venue is not being used (perhaps just before a game) and arrange a time to take your subject(s) and some lighting gear for studio-grade shots.
If you shoot sports (or any similar action) under the lights, you are likely going to experience dark frames in your take-home. Understanding that this could happen will lower your blood pressure and should be your first step in developing a game plan to compensate for the issue. Shooting action under the lights is one of the most challenging types of photography and intermittent lighting is just one of the reasons why.