Balancing strobe with various types of indoor lighting can be a challenge for sure. The reason is, different types of light emit different color casts. Tungsten (or incandescent) light is actually a warmish, orange hue (which honestly blends better with strobe light better than you might think) and fluorescent light puts off a sickly green hue. Most light from strobes is balanced closer to the sun, and a more true white.
If you plan on overpowering the ambient light, then you won't have any problems, but when you want to balance the ambient with strobe light, then you have to think carefully about how you do it.
First off, to determine what color the lighting is in any given room, set your white balance to sunlight and take an ambient only reading of the room. If it appears orange, then its mostly incandescent, if it appears green, then its mostly fluorescent. There are many other variations but in this post, I'm going to focus on gelling for florescents only.
I wanted to take a portrait of my co-worker in his office for a project I'm working on. His office is lit with standard fluorescent lighting with dingy, dirty screens so the ambient light in his office is, you guessed it, sickly green. So the first thing I did was to take an ambient only reading of the room. I set my white balance to sunlight, put my camera in aperture priority mode and took a quick test shot. I didn't even bother trying to compose a shot or focus, because this was a test for color only. I also told my co-worker just to continue working because these were only test shots.
Right off the bat, I can tell several things about this image. First off, the fluorescent lighting is indeed more of a greenish hue, which I will have to correct, but also, to use the ambient in the room, I won't be able to get a good, sharp photo without a tripod or the use of flash because the shutter will be so slow that I will pick up motion blur from the subject.
So the first thing I do, is put a flash on a stand camera left, raise it about 6 feet and point the head straight up at the ceiling to bounce the light. I want it to appear as its natural light in the room. Then I put a 30cc window green gel on the strobe (the one that came with my Nikon SB-800), shifted the white balance to fluorescent and sped up my shutter speed about one and a half stops. The reason I did that was, if I left my aperture and shutterspeed where I took my ambient only reading, then by adding strobe, I would have blown out a few areas in the scene. Then I took another test shot.
In this shot you can see right away that the color looks better (not perfect) but is better and is now all the same color which will be easily adjustable in post. If I had not gelled the flash then there would have been two color casts in the photo, green and white. No matter how good you are in post work, this is nearly impossible to correct so getting everything the same color is important. Another thing you will notice, by using flash, the image appears much sharper and crisp. If I had chosen to use a tripod and no flash, the image still would not look this sharp. The flash essentially freezes action and brings more detail to the image.
Something I noticed about this shot that I didn't like is, even though the flash is doing a good job lighting the front of the subject well, it simply doesn't have the power to light the whole room effectively and you will notice how the light fall off makes the room in the back appear darker. This is also because I dialed my shutterspeed up from around 1/10 of a second (the ambient only exposure) to 1/30 of a second. So to get a little more light in the background, I placed another green gelled flash on a filing cabinet in the back of the room, camera right, and bounced this one off the ceiling as well. I dialed this flash down in power about one stop below my key light.
Now you can see in this image the overall lighting is much better and gives the feeling of a normally lit office area. The flash doesn't call attention to itself, however the color though is still a bit greenish-blue for my tastes, but since this isn't going straight to an editor out of the camera, I can take this image and warm it up a bit in post. If I had to use this image straight out of the camera, then it would be no big deal to simply adjust my white balance in camera to add a little more warm tones.
This is the final image for this shoot. I warmed it just a bit in Photoshop and that was it. I had the lighting and exposure where I wanted it, so I didn't need to do any curves, levels or contrast adjustments. I will admit to just quickly adding a warming filter in post which was not the optimal way to do this as it warmed up areas throughout the entire photo. If I wasn't so lazy, I would have just applied the warming filter to specific areas with a mask.
So as you can see, this was a quick and moderately easy way to include strobe in an ambient situation without creating ugly color casts.
For more information on balancing strobes with ambient, check out these article by David Hobby on the Strobist blog:
Hope this helps you the next time you have some ugly, green light to wrangle!