Lighting 103: Using Gelled Flash to Correct Ambient Light

Abstract: You can alter your camera's white balance and gel your flash to "correct" nearly any ambient light color shift. But should you?



Let's go back for a minute to Lighting 101. Remember Sid Siva's portrait of director Mahmooud Kaabour, seen above? This is a good example of using white balance and a full CTO gel to tame the ambient lighting environment.

Sid merely set his white balance to tungsten (he is now balanced for 3200K) to rein in the tungsten shift from the scene's lighting. This created a cooler background palette against which to light the director.

Because the white balance in the camera was set to 3200K tungsten, Sid then placed a full CTO gel on his (snooted) flash. In that environment, the flash is seen as neutral white. So he has used his white balance setting to shift his warm background to neutral, and then used a warmed (CTO'd) flash which is also rendered neutral by the shifted white balance.

This is the classic way in which photographers have learned to tame and color shift in their ambient environment. And it often makes sense to do that. A color-shifted background can be distracting or even overwhelming. It can look like an uncorrected mistake.

But by the same token it can also create a mood or add a layer of color to a photo. Your ambient environment is a ready-made (and real) color palette that is there for the taking.

So instead of dutifully setting the white balance to match the ambient environment and then gelling my flash to unify with that new color temperature, I like to first assess when the environment is offering me. I do this by looking at the scene with the camera set to daylight white balance.

The photo featured on the very first post on Strobist, back in 2006, is a good example.


See What the Room is Giving You



As I walked into the Glenn L. Martin Wind Tunnel at the University of Maryland to assess my lighting possibilities, my first thought was to examine what was already on offer. I grabbed a full-exposure ambient light shot of the tunnel with the camera set on daylight white balance. I knew it would be out of color balance; the room was lit by industrial sodium vapor lighting.

Predictably, on daylight white balance it looked pretty bad. So I underexposed the room by a stop and looked again. It looked better—darker, but more colorful. So I dropped it another stop. Better still. And then another stop. That was too much.

At about 2 1/2 stops underexposed on daylight white balance, the ambient light took on a rich, orange hue. As soon as I saw that, I knew I had the color palette for my photo.

Sure, I could shift this environment back to neutral white—or even dial in my ambient exposure to black and start lighting from there. But do I really want to do that?

The point is, just because you can take the room back to neutral light doesn't mean it is always a good idea. Look at the room through a variety of exposures (done in daylight white balance) to see what it can give you. Often, you'll find a good starting point against which to light.

I added some light with a bare, ungelled speedlight. It was 2006, and I was not yet considering the idea of gelling my flash to make the subject better fit into a non-white ambient environment.

But today, I'd probably do things differently. Let's take a look at a photo in a tungsten environment to get a better idea of how this would work.


Gel Your Flash to Better Integrate Your Subject



Our eyes partially correct the color shifts in ambient environments. But we can still see that open shade is cool, or tungsten light is warm. That said, tungsten light looks a lot warmer to the camera than it does to our eyes.

When photographing someone in a warm light environment you can bridge this gap by using gels to split that difference. Strobist reader Leandro Ilha, based in Porto Alegre, Brazil, did exactly that by lighting himself with a 1/2 CTO in this tungsten-environment self portrait.

The color palette in the photo is keyed by the warm lamp in the background. (These days who can tell if it really is a tungsten bulb, as they are quickly going the way of the dinosaur. It might just as well be a warm CFL or a 3200K LED.)

Whatever it is, it is very close to a tungsten bulb in color temperature. And that light is glowing in the back of the scene.

Leandro shot on daylight white balance to let the warm lamp express itself. And in doing so, he let the warm ambient color become his palette. If he lit himself with white light, there would have been a disconnect. If he lit himself with a full CTO gel on his flash, his skin would have looked unnaturally warm. It would have matched the ambient light, but it also would have been warmer than our eye (as opposed to our camera) perceives tungsten light to be.

Instead, he lit himself with a 1/2 CTO gel. This splits the difference between daylight and tungsten, and comes much closer to the way that we physiologically perceive tungsten light.

Leandro then finished off the scene by filling in the gaps in the room with a second light. It was fitted with a full CTO gel, bounced off of the floor at camera left, and underexposed. This kept the room from going black in the areas lit by neither the key light nor the lamp.

Keeping everything in the CTO family ties the whole frame together. But he could have just as easily put a full (or half) CTB on the bounce/fill light to create some cooler color tension in the shadows as well. This way, the lamp and his face (presumably lit by another, unseen lamp) would stand out more.

Which is right? It's a subjective choice. It's whichever look (unified warm, or with color tension) that Leandro preferred.

What is not subjective though, is that a "white" flash would have created a logical disconnect, and would have made the photo look less natural and more lit. Because there is no reason for a white light to be in that scene.
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The first step for me towards better understanding the color of light in my photos was to learn not to use my white balance adjustments to beat the color into submission.

Look at it in daylight white balance first. Deepen the exposure a little. See how it looks.

If you can use that pre-existing color to your benefit when lighting the scene, it'll give you a ready-made color palette that is perfectly appropriate—because it is what is really there.

Next, you can use gels to marry your flash to the existing light. Often, this can be done by splitting the difference between the actual color shift and white light, i.e., using a 1/2 CTO in a full tungsten environment.

This approach of "splitting the difference" also works well for allowing the camera to render a non-white color more closely to the way your eye would see it.

ADDITIONAL READING:

In the Heisler book, turn to the back half of the book and browse through the color portraits. Next, go to page 220 in the "Picture Specifications" section and note how many of those people were in fact key lit with a 1/2 CTO gel. I was pretty surprised when I did this.

I have always thought of a 1/2 CTO as a pretty extreme warming gel for daylight-balanced portraiture. But if your key light is such that it could have logically have been coming from a natural, ambient incandescent source, the 1/2 CTO gel is a very effective way to make the camera express tungsten light in the way your eye would have seen it.

NEXT: Color-Shifting Ambient Environments