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Lighting 102: 6.1 - Gelling for Fluorescent

On their face, gels are a pretty simple concept. You stick a colored piece of plastic in front of your flash and it alters the color of the light accordingly. But so much is possible from just this simple trick.

In this, the first of a four-part section on using gels, we'll be looking at their most common use -- converting the color of your flash's light to the color of the ambient light in which you are shooting. This is called color balancing.

We first visited the idea of color balancing in Lighting 101 where the two most important gels were discussed. The "window green," (or "plus green") gel converts the light from a flash to nominally match that of a fluorescent light.

A "CTO" gel similarly converts your flash's light to match the light from an incandescent (i.e., tungsten) bulb. But for today, we'll be talking about just the little green gel. It's certainly complicated enough to merit its own post, as you'll soon see.

While the fluorescent conversion used to be a simple process, this is no longer the case. But for the sake of discussion, let's assume that it still is. At least for the moment.

Traditional fluorescent light is green. About 30 color correction (CC) units of green, to be exact. By placing a 30cc window green gel on our flash, you make the flash's light match that of a traditional fluorescent environment.

If our ambient is green, and your flash is green, you're okay. Because you can correct for all of this similarly green light by setting your camera on the fluorescent light balance, and all is white again. This is because the FL white balance setting just shifts everything over 33 units of magenta. This is what balances out the green.

Take, for example, this shot I made a couple of weeks ago at Western Kentucky University, while teaching the PJ students there.

(Sorry, Jeanie. You were my most recent example...)

This is a fluorescent-lit studio. In this shot I lit Jeanie with an SB-800 in an umbrella and the flash was gelled with a window green gel. My shutter speed was opened up to let the background of the photo burn in to make a decent exposure.

But in addition, the green gel, combined with the camera on fluorescent setting, brings the colors up pretty close to correct. None of that sickly-green cast that happens when you forget to gel your flash and the fluorescents just come in the ugly green way they really look.

Pretty simple technique, right?

But in practice, there are two little gremlins that usually come into play. First, rooms can often have a mix of fluorescent and daylight. Maybe even a little tungsten thrown in for good measure.

In addition to that, fluorescent lights are now all over the map, color-wise. In reality, they can now actually be warmer than tungsten.

Let's take these problems one-by one.

First, on the multi light sources, sorry to say that you have to choose a source color and go with it. But this can be better than it sounds. My first trick, if there is a lot of daylight bouncing around in a fluorescent room, is to ask if I can turn off the overhead lights while I shoot.

If the daylight is enough to cause light balancing issues, there is usually more than enough to work by with the fluorescents turned off. Then you do not balance at all -- just shoot in the daylight with normal flash.

If that solution is not available, I will close the blinds or drapes to minimize the encroaching daylight. (This daylight comes through as magenta when you are set on fluorescent white balance.) One other thing you can do to help are to work on the opposite side of the room as the windows, to minimize the daylight contamination.

If you have a mix of fluorescent, daylight and tungsten, do everything you can to lose the fluorescent light. Then shoot on daylight with no color correction gel on your flash. The daylight and tungsten will mix a lot prettier than any green/other combo will.

(And if all else fails, hope it runs in black and white...)

And as we said earlier, fluorescents are no longer just 30cc's of green. And for us photogs, that really sucks.

There is no good solution here. The important thing is that you have to be able to counteract your conversion gel with a white balance camera setting. That is to say that, even if your fluorescent light is not a perfect green, you pretty much have to live with the difference. Just green your flash and neutralize it (the flash) with the FL white balance setting. Sometimes the ambient will go a little weird. But it is better than not gelling at all.

For those super warm fluorescents, the ones close to tungsten, I will usually just treat them as tungstens. I'll CTO the flash, and set the white balance on the camera to tungsten. Again, not perfect. But better than nothing. And the flash-lit part will look good.

How can you tell where the fluorescents are, color-wise? The easiest was is to shoot an ambient-only shot and chimp your screen. If it looks more green, gel and balance for fluorescent. If it looks more orange, treat it as a tungsten. This is also a good approach for working in vapor-based light (sodium, mercury, etc.).

Your flash-lit subject (usually the most important part of your frame) will be okay. The ambient burn-in part may be a little off. But that's the price we now have to pay for having 57 varieties of fluorescent bulb colors.

And as for dealing with tungsten lights, we'll be hitting that in the next installment of Lighting 102.

NEXT: L102 6.2 - Geling for Tungsten


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