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I took a bunch of photos at my son's martial arts club using a D90 with a 50mm F1.8. The club is lit with overhead fluorescent lighting, and I was getting some weird results where some shots are "white", others have an "orange cast", and still others are partly white and partly orange in the same shot.

I suspect it has to do with the combination of the frequency of the light flicker and with the camera shutter speed. Here is a sequence of 3 shots that show the problem. The shots were taken with 1/500s at F2 and ISO-800 and with Auto-WB.

First shot ("white/normal"): alt text

Second shot ("orange cast" at top): alt text

Third shot ("orange cast" at bottom): alt text

These were taken in burst mode within a second of each other.

Can anybody tell me what is going on? And, how I can avoid this?

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you just gave me an idea for something to try out. –  msarchet Oct 21 '10 at 14:20
    
Hope you let us know how it turns out... –  seanmc Oct 22 '10 at 3:49
    
It has to do with light flicker, and the alternating current that flows through the flourescent lights thus changing the color. –  J. Walker Mar 27 '12 at 13:50

6 Answers 6

up vote 59 down vote accepted

Fluorescent lights can flicker at twice the frequency of the current feeding them, which implies an entire cycle of the flicker will take between 1/100 and 1/120 second. During each cycle the light's intensity and its color temperature can change. Thus, if you're using a shutter speed of 1/100 second or faster, you might observe exactly these phenomena: your photos make an interesting document of them, especially the bottom photo.

Details appear deep within a good Wikipedia article on fluorescent lamps under the heading "Flicker Problems". The article references "The Feral Photographer" blog which gives a brief (simplified) explanation from a digital photographer's perspective.

For sports photography indoors you need a short exposure time to freeze the action. Consider flash options if they are possible. Very short exposures (down to 1/4000 second typically) can be achieved with HSS flashes. To an extent you can adjust the color balance, especially when you're shooting RAW images, but that's going to be tricky during the color transition.

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9  
+1, these photos are a great way to demonstrate this issue. –  sebastien.b Oct 21 '10 at 4:39
    
thanks for the response and the links. Flash is not an option, so I guess I just need to shoot a lot, pick the best ones, and correct the WB where possible! –  seanmc Oct 22 '10 at 3:59

If flash isn't an option but you're there officially and reasonably close to the action, what about halogen floods (poor man's studio lighting if you like). Many years ago I had some cheap 8' tripod mounted 500W floods designed for DIY work, modified to 3x500W each.

Something similar may work here, at least to reduce the contrast from the fluorescents to something more manageable. You would need 2 or more stands and to work between them to avoid the shadows being too intrusive, and multiple lamps per stand significantly softens the edges of shadows.

LED based and high-frequency fluorescent lamps would also work, but to get the intensity would end up costing a lot.

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Shoot it at 1/125th and your color problems will be solved. Having a shutter that slow negates the effects of a rolling shutter. I believe the lights cycle at 120Hz. Shooting at 1/125th will give you one full sine wave and thus the best color results. It doesn't matter if the lights are on separate circuits and out of phase with one another.

Shooting at 1/60th gives you 2 full sine waves and the same color, but you have to worry about motion blur much more.

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Even 1/125 is too slow for action shots. Trying to freeze a kick or a throw requires a faster shutter speed. –  seanmc Feb 28 '13 at 13:20

I've had exactly this issue over this past weekend covering a national karate championship with 4 other shooters. Flash was not an option. For the multi coloured image which won't respond to one simple colour temp fix, I intend using Lightroom 4's new feature of painting with temperature and tint, a sort of roving gelled brush. Only doing it for the print orders, not for the 4300 now posted to my gallery. They have been near enough is good enough with an explanatory note on the first page. An added issue in our case was the cast from the blue floor mats and the ambient through some windows

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As others point out the lights are essentially blinking different colors during your exposures. What's worse is that different flourescent lights are on different circuits, so may be out of phase by 180 degrees, and unless they installed the same temperature color bulbs in all the fixtures (unlikely), color variations through a cycle will be even greater.

Your camera complicates this by using a rolling shutter above a given speed (usually around 1/200. This means that only a portion of the image sensor is exposed to the scene at any given time, so if the light changes during the exposure, the color change will only affect a portion of the image sensor.

Lastly, since the color temperature is changing, the camera can't get a good grip on white balance for exposure.

You have a few options:

  • Decrease the speed so you get at least one full cycle of light (1/60th in the US, 1/50th elsewhere) per exposure
  • Overpower the local lights with flash (which also has limitations above the 1/200 sync exposure, but high end flashes can take care of this for you)
  • Take a lot of raw photos and note areas where color references can be used to white balance the photos in post-processing for those shots where the color doesn't change mid-exposure
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To see what the shutter sees, make yourself a stroboscope by cutting a cardboard circle from a cereal box, about 6" diameter. Cut a small radial slot near the edge of the disk, put a spindle through the center, and arrange to spin the disk while looking through the slot. First time I looked at a fluorescent light through this was a real eye-opener! –  gbarry Oct 21 '10 at 22:25
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I'm assuming the rolling shutter is responsible for the half-and-half look with white/orange in the same photo? I suspect that it would be difficult to correct WB on the half-and-half shots (can you apply WB settings from one photo to half of another one?) Presumably, the boundary area will be the biggest problem. –  seanmc Oct 22 '10 at 3:53
    
@seanmc - Yes, the rolling shutter, coupled with the changing light conditions results in the half and half photo. If it was important to save that one shot, I imagine a custom white balance could be applied using photoshop and masking. You are correct that the boundary region would require special attention. –  Adam Davis Oct 22 '10 at 12:29

Fluorescent lights are terrible news for photography, and this is just one of the reasons! They give out light which is missing a big chunk of the red spectrum, which can make skin tones look greenish and unhealthy, they are usually different colours from each other even if the tubes are the same type, and they change colour during the power cycle!

Your options are to sync your shutter speed with the lights, by shooting at 1/25s 1/50s (assuming 50HZ mains frequency) but this isn't good for action photography. Your other option is to reduce the shutter to 1/250s and use an external flash on full power bounced off the ceiling. The short flash duration will help freeze the action. HSS is possible but you might have difficulty overpowering the ambient light as this option costs power! If you still want to use burst mode an external power pack will be needed.

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As whuber mentions, lights flicker at twice the mains frequency - once on the positive swing, and once on the negative swing. Therefore, you can get away with a shutter speed of 1/100 for 50Hz mains frequency. –  Evan Krall Oct 21 '10 at 21:30
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The exact frequency depends on what type of ballast is installed, and there is the possibility of two tubes being out of phase for the same power supply depending on how long it takes them to fire up, so while you may be able to get away with 1/100s, slower shutters speeds often work better in practice. –  Matt Grum Oct 21 '10 at 23:05
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Unfortunately, using a flash isn't an option (too distracting during the classes). I think taking a lot of shots and picking/correcting the good ones is my best option. –  seanmc Oct 22 '10 at 3:54
    
It should probably be noted that fluorescents designed specifically for photography/videography (KinoFlo and similar) are much better news: the combination of arc vapours and phosphors used pretty much eliminate spectrum deficiencies (you might have trouble exactly matching a fraction of a percent of Pantone); the ballasts have their own oscillators that operate well into the kilohertz range; and they are usually dimmable (using pulse width modulation) without an appreciable effect on colour balance. That said, these lights aren't cheap, and they're not what you'll find on location. –  user2719 Jul 18 '12 at 20:54

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