The 90-Percent Rule Of Lighting In Photography

It’s About Absorption And Reflection

You often hear about percentages, sometimes in statistics, like 75-percent of all statistics are made up, which often leaves you wondering about the accuracy of such numbers, but when it comes to photography, one percentage that is accurate is the 90-percent rule of lighting. It’s not just a rule, it’s a fundamental and principal of photography every photographer should comprehend, after all, lighting is the lifeblood of an image and without light, there is no photo.

It's easier to photograph a light complected model in a light top like this photo of Jenni, due to the 90-percent rule of lighting in photography.

Simply stated, the 90-percent rule applies to reflected and absorbed light. Whatever is pure black, will absorb 90-percent of the light that strikes it, whatever is purewhite will reflect 90-percent of the light that strikes it. As simple as that seems, many photographers forget the other part of the rule, there is 10-percent light reflected from pure black and 10-percent of the light absorbed from pure white. The key word in all the states about the 90-Percent Rule is “pure.”

However, a photographer must comprehend that not all black or whites are pure, though many are close. So to use the 90-Percent Rule effectively, a photographer must learn to judge shades of gray, or all the tones and mid-tones between pure white and pure black. In photography, black and white and the shades in between are not colors, they are tones and some tones are more reflective than others. The darker the tone, the more light it absorbs and the less it reflects, the lighter the tone, the more light it reflects and the less it absorbs.

Once a photographer understands everything to the black side of the tonal scale (left area of histogram, shadows) is absorbing more light and everything to the white side (right area of histogram, highlights) of the tonal scale is reflecting more light, we can apply this when metering our subject that is illuminated by artificial light. If we build a set, then meter it and the result is F/8 off the flash meter, that would be the actual aperture we’d use to properly expose the set, however, throw in a model/subject in the set and now you’ll have to consider her skin tone because as photographers we should expose for our subject, not the set. So what tone is our subject? Is the subject darker than middle gray? Is our subject lighter? How much darker or lighter? These are things a photographer must take into consideration to adjust their exposure.

Now many will argue about the accuracy of the meter based on 18-percent gray, a middle tone is all that is needed, but in reality, when you take the 90-Percent Rule into account, it’s only true for the scene, not the subject. The flash meter is measuring the light falling on the subject, incident light, not the reflected light the digital camera’s sensor will capture from the subject’s actual skin. Learning to judge how much light a model’s skin will reflect takes skill, but the easiest solution is to stop down 1/3 of an F/stop for lighter than average skin tones and to open up 1/3 of an F/stop for darker than average skin tones.

Think of your incidental flash meter as starting point based on 18-percent gray, similar to the meter in your digital cameras (DSLRs). The color of 18-percent gray is close to the average gray of street asphalt (not black top) found on most highways and parking lots. I’ve worked as a photographer/photojournalist in almost 40 countries, photographed tens of thousands of people and I still have not seen anyone with asphalt gray skin tone.

When photographing a dark subject, or in this case dark clothes against a dark background, use white V-flats on each side of your subject to bring out separation and detail as in this photo of Candice.

During a photo shoot, I will consider the skin tone of my subject, or the correct exposure for my subject’s skin tone, I then look at the actual scene and adjust my lighting to match—it’s like the rule of posing, pose the model first, then light for the pose. In essence, I light the model first, then light the set. As example, since this article focuses on the 90-percent rule of lighting in photography, let’s pretend we’re photographing a dark subject against a dark background and we must maintain that dark background. If the lighting is improper the subject will disappear into the background and/or the background will not appear as dark as it was intended.

While sometimes no separation of the subject from the background can make for interesting photographs, it’s usually more appealing to create some separation of the subject from the background, which is easily done by simply understanding the 90-percent rule of lighting in photography. Separation of the subject and the background also makes our subject standout or appear in front of the background—an important element in people photography—in addition to the fact that many art mediums like photography are two-dimensional, separation will often add another dimension in the overall photograph.

When photographing white on white, use black V-flats on each side of your subject for separation from the background and to provide detail in your subject's clothing.

Since we see in three-dimensions, any third dimension illusion we create through lighting provides for a more effective photograph. In the above situation I painted a dark subject against a dark background, or a low-key scenario, though the 90-percent rule applies just as equally when a photographer is faced with a model dressed in white posed in front of a white background, or a high-key set. Whether it’s a low-key or high-key scenario with matching backgrounds and subjects, if a photographer understands the 90-percent rule of lighting in photography, the resulting image will reflect this grasp of knowledge.

For example, let’s take white on white. The key here is to take at least two, black foam-core panels and place them on each side of the subject as close as possible without intruding on the frame of the image. These black panels help subtract light from the sides of the subject while reflecting some black tone back into the subject’s sides. This affect will create an effect of a thin outline of the subject’s white clothing and add detail into the subject’s clothes from the white background, thus the badly needed separation of the subject from the background is created through the absorption and reflection of light.

The same happens with black on black, a photographer simply has to place a white foam-core panel on each side of the subject so the reflected light from the white will have the edge-building effect on the subject’s clothing. It’s all about separation through absorption and reflection based on the 90-percent rule of lighting in photography.

When using these white and black foam-core panels, or cards, simply place them parallel and close to the sides of the subject without physically entering the camera image frame. This method works great when you only have two cards, though the ideal method is four cards, two on each side and affixing them together with gaffer’s tape to form a V-shaped wall with the V-point facing away from the subject. Ideally 4-foot by 8-foot foam-core boards work best, especially if you use the type with black on one side and white on the other side. This is more efficient since you simply rotate the V-flats to use the side you need for a given scenario.

My first book cover featuring Playboy Playmate Holley Dorrough involved using black cards to bring the detail in her platinum blonde hair out.

Now this technique is not limited to high-key and low-key studio scenarios, let’s take the hair color of a model as an example. If your model is platinum blonde haired, with dark, tanned skin, her hair will obviously reflect more light than her body. The human eye is forgiving, so we don’t notice the difference, but the camera is not forgiving, it only captures reflected light accurately based on our camera settings. Thus the potential for blown-out highlights, the hair in this case, is highly probable.

Obviously we’re exposing for her skin so this will cause the hair to overexpose, though the solution is simple, have an assistant hold or place black cards, again out of camera frame, around her head to reflect black tone back into her hair, as I did in my first book cover of Playboy Playmate Holley Dorrough.

In summary, as a photographer, knowing that the 90-percent rule of lighting in photography is not a made up statistic but a highly accurate number, plus understanding how it impacts every element in a photograph, can make our photography great and not mediocre. With that I close, as in all my books, let’s not forget the men and women who serve our country to protect our freedoms, God Bless them all, their families and friends, Rolando.

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