Saturday, June 13, 2009

Photographing under fluorescent lights

When out taking photos under fluorescent lights, you may have noticed weird things happening with your images such as the color temperature and/or exposure shifting between frames even though you haven't changed your settings. Here's an example of what it might look like (photos were taken in rapid succession in Manual mode):

The reason for this is simple, fluorescent lights flicker. Too fast for your eyes to see, but depending on your shutter speed, your camera may be able to pick up the fluctuations. If the light uses a magnetic ballast, it will flicker "off" 100-120 times a second (2 times for every cycle of the 50-60Hz line power). At high enough shutter speeds, one frame might be taken while the light output is at its peak, and another frame taken while the light is at its lowest resulting in significant exposure differences. At slower shutter speeds, the fluctuations end up being integrated together so you won't notice a difference between frames.

The good news is many if not most fluorescent lights you encounter now use electronic ballasts that operate at 10kHz or more, which means the flicker is too fast to be a problem for normal shooting. Under magnetic ballasts, you can try to use a lower shutter speed and/or bracket and this will usually solve the problem.

One interesting note is many people are noticing this phenomenon for the first time with digital cameras and think it's an issue with digital. This is a misconception of course because the same exact thing will happen with film. The only difference was back in the film days, we rarely shot with film above ISO 400 or 800 because the photos would look too grainy. Digital cameras now however have so little noise (some DSLRs like the Canon 5D Mk II or the Nikon D700 produce images at ISO 6400 that look better than some 400 speed film!) that people often shoot at high ISO settings all the time, which means higher shutter speeds that better reveal the flicker. Also with digital we shoot more frames because it doesn't cost anything and can instantly review the image so more people are noticing the problem. If you see it though, don't worry and don't return your camera, just follow the advice above and keep shooting.


Anonymous said...

Energy efficient light bulbs are the easiest first step consumers and businesses can take towards reducing their energy consumption. Products have gotten light years better in the past few years and, in my eyes, indisputably better for 99% of applications. Both CFL and LED light bulbs run much cooler than incandescent bulbs, use energy much more efficiently, and do offer saving on your electricity bill. I am a vendor of energy efficient bulbs, so perhaps I am a bit biased, but I don't know why everyone doesn't switch today.

sam said...

i love this blog,i like under fluorescent can put bulb under fluore. bulb can be run throughDigital ballasts.if you use digital ballast then you can save your electricity bill.