If you have a shoe-mount flash, like the Nikon SB-900, you probably noticed that it comes with a set of colored gels. Depending on your level of experience, you may think that these gels are used to create color effects in your images (true), or you may just put them in the case in your closet. Let’s take a look at how these gels work and what you can use them for.

Gels are used to change the color of the light emitted from your flash or strobe unit. The original intent of most gels is to allow you to have a uniform color temperature in your scene. Without any correction, your flash emits light that is more or less daylight balanced. This is great when you are shooting outdoors, or when your flash is the only light source. All you need to do is set your camera’s white balance to “sunny” or “flash,” and your subject will have the proper color rendition. But what happens when you’re trying to use fill flash and the ambient light isn’t daylight balanced?

Scenario #1: Balancing out tungsten (incandescent) lights

Let’s say that you’re indoors shooting an object that is illuminated by traditional tungsten lights. Most incandescent lamps have a color temperature that is very low (3000°K). Instead of “white” light, tungsten lamps look yellow/orange. To correct this, you could simply set your camera WB to incandescent (tungsten). So far, everything’s fine. But now, if you need to add some fill flash, you have a problem. The flash produces a daylight-balanced light (~5200°K), which will be perceived by the camera as blue if you’re set to incandescent WB. Now your subject is blue where the flash hits it, but the other elements in the scene are neutral white.

The solution in this scenario is to use CTO (color temperature orange) gel to make the light from the flash match the incandescent lamps. By adding the orange gel to your flash you can keep your camera’s WB set to incandescent/tungsten and have uniform color balance throughout the scene.

Scenario #2: Balancing fluorescent lighting

In this scenario, you’re shooting indoors where the ambient light is coming from fluorescent light tubes. If you ever shot daylight balanced film indoors with only fluorescent light, you probably noticed that everything looked kind of green. Standard fluorescent lamps will look greenish if you’ve set your camera WB to “daylight.”

Again, you can use the same trick as in Scenario #1 to create balanced light if you’re using fill flash indoors under fluorescent lighting. Set your camera’s WB to fluorescent, and then place the green gel on the flash. The green gel allows your flash output to match the color temperature of the ambient fluorescent tubes, and everything should look balanced in the scene.

Scenario #3: Creative use of color gels

While CTO (orange) gels are designed to help you balance out light sources, you can also use them to create subtle creative lighting effects with your digital camera. You can add a warming effect, or create dramatic orange/blue color contrasts in your scene by using gels and setting your camera WB appropriately. The trick is to set the camera WB to match the proper color temperature of the light falling on the subject, while allowing background elements to shift in color.

Example #1: The blue background

In this shot, we set up two lights. One SB-800 speedlight in the background was set up with a very mild blue gel (although you’d get a similar effect with no gel), while the subject was illuminated by another SB-800 with a CTO (orange) gel. If I set the camera WB to daylight, you get the following image. The subject is way too orange, and the background, while blue, is fairly neutral.

Compare this with the final image, where I changed the camera’s WB setting to incandescent (3000°K). Now, the subject has the proper skin tones, but the background is rendered a delicious shade of blue. You can also use this technique in outdoor scenes, especially right at twilight during the “blue hour.” Setting your camera WB to tungsten will make the sky and background a deep blue color, and then use a speedlight with an orange gel to get the proper color on your subject.

Example #2: Warming a background

In this shot, I wanted to create a warm lighting effect in the background, and also make the “candle” have a warm appearance. Because I knew that tungsten lights will look warm (orange) if I have my camera WB set to daylight, I took the following approach. I lit the subjects with a single SB-900 speedlight in a softbox. The SB-900 had no gel on it, so it would be daylight balanced. I then placed a second SB-900 speedlight behind the couch and put the orange CTO gel on it. I set my camera WB to daylight to match the strobe that was illuminating my subject. The other lights (background SB-900 and candle) then look nice and orange, providing the scene with a warm mood.

Getting gels for your flash unit

Most camera manufacturers will sell gel sets that are made to fit your particular flash unit. You can also make your own sets by cutting out strips of bulk gel sheets. I know many photographers who will cut out small strips of CTO gel and then attach them with Velcro to their speedlight. Store the strips in a small filter wallet and you’ve got a handy color kit to go with your flash units.

Be sure to check out Field Notes, the new photo eBook by Jason P. Odell