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This article is part of the ‘Portrait Lighting For Beginners’ series. This series is meant to help you go from a beginning photographer to making beautiful portraits.

I wonder how many of my readers ran like the wind when they read the title of this post. “Oh crap, here he goes talking about laws of the universe and physics, I’m outta here!” Not to worry, I’ll keep this short, to the point, and most importantly, simple. So here we go.

The Basic Laws (In no particular order)

1. Large light sources give you soft light, and small light sources give you hard light.
2. The closer a light source is to the subject the softer the light, and the farther away the light source is, the harder the light.
3. The closer a light source is to an object, the brighter it is.

Law 1. Size and Softness
This one seems pretty straight forward. The larger the light source is, the softer and more diffuse (or fuzzy) any edges of light and shadow will be. A tiny pinpoint light source will give you hard shadows. For portraiture, larger light sources to achieve softer lighting is traditional. This is accomplished using umbrellas, softboxes, and other tools which we’ll talk about shortly. That’s not to say that soft light is best, it’s just traditional.

To see this rule in action, try a little test. Sit your significant other down on the couch next to a table lamp. No significant other? Try holding your foot out, but keep an eye out for the neighbors, because believe me you look foolish. Good. Now take off the lampshade and observe the hard, bare bulb light that comes from the small light bulb. Put the shade back on and observe how the light becomes soft because the shade is now the light source, and it’s a lot bigger than the bulb. Doesn’t your foot look nicer in soft light? Or maybe that hard light was hiding something you didn’t want seen in the shadows. There you go, that’s why you shouldn’t be afraid to break the rules. But I digress.

Easy enough, right? Big = soft and small = hard. On to law 2.

Law 2. Distance and Softness
After reading the first law, you might ask “Hey, but the sun is as big a light source as we know here on planet Earth. Why is the light from the sun so hard?” That’s a good question, and any book on lighting uses this example when explaining the laws of light.

The sun may be huge, but the distance is so great, that its apparent size to us is tiny. So this one really just flows right into the first law. If you were to take a one inch light up close and a ten inch light ten feet away, when looking at them, they would appear to be the same size. They would have the same lighting effect (as far as softness, intensity comes next).

So while a Speedlight flash might seem small and give hard lighting when taking a picture of your girlfriend, that same light would give you very soft light when it’s positioned right up next to a ladybug. The close position makes it seem enormous, and thus softer.

Law 3: Distance and Intensity
Okay, if you’re still reading, you know that this stuff is really easy. Don’t fail me now. This is the hardest part, but still really simple.

Light diminishes rapidly, and not in a linear way. This is known as the inverse square law. Now, if this were a physics class, I’d go ahead and explain it, but since we’re photographers, and thus creative beings, I’ll leave that alone. Math? Screw that.

Here’s the meat of it: the further away a light gets from an object, the less light falls on that object. The key here is that changes in distance have a bigger effect the closer the light is to an object. If you have a light set up ten feet from an object and you move it five feet back, it’s going to have a much bigger effect than if you moved it from 100 feet to 105 feet. The first move would be dramatic, while the second would have nearly no effect whatsoever.

If you really want to know the details, here they are, but without all the math and fractions. We’ll think of this in terms of stops (a measure of light). To decrease the light falling on an object by one stop, simply double the distance to the object. To increase the light by a stop, cut the distance by half. To increase it by a stop again, cut the distance by a half again, but this time a half of the new distance, not the original distance. If you take a minute to stop and think about this, you’ll quickly understand the ten foot vs. 100 foot example above. Moving five feet from ten feet decreases the light by roughly half a stop, whereas moving five feet from 100 (where it would require a 100 foot move back to decrease the light by a stop) is next to no change.

The key here is that light increases and decreases in a very predictable way, and now that you know the law, making adjustments with your lighting will be much easier and less hit and miss. Sometimes when taking pictures, it’s easier to just move the light than to adjust the power setting because it’s quicker, and because you know exactly what the effect will be thanks to the inverse square law.

Here’s the best news of all: f-stops on your camera work the same way. When you hear someone say “that’s about a stop lighter in that area than this area”, what they’re saying in technical terms is that there’s one unit less light in the lower lit area. This works out beautifully, because you can think of your camera’s settings and light intensities in the same way. The trick is to practice taking photographs and to learn just what a stop really looks like in the real world to your eyes. It takes a little practice, but is actually really easy to get.

Most explanations of the inverse square law involve a bunch of math and trying to wrap your head around concepts. The way I look at it, if you spend more time trying to figure out numbers than actually taking pictures, you’re doing yourself an injustice.

Exercise
What? Homework? Yeah yeah, I put that there for fun. But there are a couple of things you can do before we start the next section to help you understand light better.

1. Try the lamp shade trick above.
2. Try some pictures with different size light sources and observe the effects.
3. Try taking some pictures in a dark room with nothing but a single lamp. Take a picture, then have the subject move double the distance from the lamp. Take another picture. Observe the effect on the intensity of light. Have the subject move again and take another picture. Now, start over, but at each step, change the camera’s exposure (use manual exposure mode) to allow one more stop of light to enter. This means the shutter speed is slower or the aperture is wider (or a combination). If the subject moved the right distance, the exposure on that image and the previous step should be the same, with no drop off in light.

Got questions or comments about this post? Why not post them in the discussion thread dedicated to this series of articles? I promise, there are no stupid questions, only stupid people. Just kidding, none of those people read this blog…

It just so happens that David Hobby over at Strobist wrote a post about this very same topic at the same time I did. He did a great job of explaining this concept, but with a little different twist on it. I highly recommend you read it. It can only do you good.

EDIT (7/9/2007): Mr. Strobist created a new post today that explains in depth the idea of apparent light size. I give it a thumbs up, and recommend you check it out.