1. Gels can be used very simply for color correction in mixed lighting situations. One of my favorite uses for an orange gel (technically called a CTO, for “color temperature orange”) is on a portable flash when shooting indoors. Indoor incandescent lights are typically tungsten balanced, which our cameras see as orange when set to a flash or daylight white balance. And if you balance for that tungsten light, the flash will look much too blue. To remedy this, place an orange gel over the flash and simply tape it into place. This will “correct” the color, shifting it to a lower Kelvin temperature to match the tungsten balance of incandescent lights. If you’re looking for a simple way to start using gels, this is it.
2. For photographers who want studio lighting control, gels are essential. Instead of investing in seamless backgrounds of every color imaginable, savvy photographers use gels to change the color of those backgrounds.
With a white or gray wall, for instance, a strobe light covered with a blue gel (held in place by clipping to barn doors or safely in front of a parabolic reflector, taking care not to let the gel touch the bulb itself) can turn that background blue.
Depending on the ratio of the background light to the key, the light can in fact become everything from deep dark blue to a light pastel sky blue. The trick is to adjust the background illumination relative to the key light. With a key light exposing a subject at, say, ƒ/8, a blue-gelled background that also meters at ƒ/8 will likely be sky blue.
Increase the output on the background light to a meter reading of ƒ/11 or ƒ/16 (one and two stops overexposed compared to the f/8 key light) and the background will get lighter and less saturated, looking more and more pale and pastel. Underexpose that background (by turning the power down until it meters at ƒ/5.6 or ƒ/4) and the blue background will get deeper and darker.
Bear in mind that when using gels to color the background, any white light that spills on the background will sap the saturation and drain the color. For this reason, it’s imperative to not only to position the subject far from the background, but it also helps to position the key light close to the subject so any spill will fall off sufficiently and have minimal impact.
Using carefully positioned flags to block the key light from spilling onto the background is an even better method to ensure good saturation from the gelled lights.
3. For funky illumination of the subject, nothing works better than a gelled light. While I sometimes choose gels based on colors in the subject’s outfit (or even, as in the example here, hair), one of my favorite approaches is to mix different colors for the key and fill lights. One can be a neutral/white light (for the key, for instance) with a gelled light as fill or both lights can be complementary colors—providing a warm red key, for instance, and a cool cyan fill.
Controlling spill is essential here in order for this technique to work. I start by adjusting one light at a time, positioning the key in such a way as to create a strong shadow on one side of the face and bright illumination on the other. A side-lighting or split-lighting position works very well for this. Next, position the fill light where it will illuminate the shadow and not spill much onto areas already covered by the key. This will ensure not only that the colors remain distinct and well saturated, but also that you don’t muddy the waters with the appearance of multiple keys.
I suggest starting with a fill light that meters at least one stop under the main light and adjusting from there. A little bit of gelled light goes a long way, and the beauty is what you see is what you get. If your mixed gels aren’t creating the effect you’d hoped for, you’re probably suffering from spill. Use strategically placed flags to ensure each light is not interfering with the other. This is true not just for gelled key and fill lights but also for gelled light on the background.