Shooting In Fluorescent Lighting
Kind of a boring post today but maybe it will save someone some trouble. While snapping pictures in the hospital recently I learned a lesson about shooting in fluorescent lighting situations. I already “knew” about this but had never experienced it firsthand and didn’t think about it ahead of time. The problem boils down to the fact that certain types of fluorescent light fixtures do not produce steady light. It may generally appear to be a constant light but is actually flickering at some multiple of the electrical supply frequency (the dominant frequency depends on the ballast, type and age of the bulbs, etc.). I forgot about this and snapped a bunch of pictures without chimping and ended up with a bunch of wigged-out shots.
How does that affect your pictures? In the image above notice that my wife’s hand is not color matched to the rest of the image (I attempted to make corrections in this image — it was worse to begin with). Also check out the images below (sorry for the boring subject matter). The images were shot in sequence with the same settings (f/2.8, 1/350s) but you can see extreme variations in the frames. What happens is that if you use a shutter speed that is faster than the length of one “flicker” (one power cycle of the light) you get variations in the image depending when your shutter opens up relative to the light variation. One time the shutter opens when the light is at its brightest and all looks normal-ish (as much as it can under fluorescents). Another time the shutter opens as the light is dimming and so forth. In actuality the color temperature also varies at different points of the power cycle which causes the weird color banding you see in these shots.
Once I bumped my shutter speed down to 1/30s (and went to f/11) I consistently reproduced the image below.
After a little research I found that most newer fluorescents are designed to operate in a way which avoids most of these problems. However, if you run into issues with old lights you can work around them. Ideally, just turn off the fluorescents and use natural light and/or flash. If your camera works reasonably well at high ISO use it to your advantage and crank it up in order to turn off those lights. If turning them off is not practical you can add light with a flash to reduce the effects or use a shutter speed which is longer than the period of the light. In other words, if the light is flickering at 120 Hz (120 times a second), use a shutter speed somewhat slower than 1/120s. This makes sure the shutter is open during at least one full cycle of the light. I found that 1/60s eliminated the problem at the hospital although with some lights you might have to slow it up even further.
Hopefully that made some sense to somebody. I tried to explain what can be pretty technical, in non-technical-ish terms. Shooting flash and balancing its color with fluorescent lighting is a whole other topic too…go to to strobist.blogspot.com or your favorite internet photo resource for info on that. There’s also some interesting info on this on Nikon’s site (includes a nice visual using a gray card).