The inverse square law is one of my favorite nerdy photography topics.
I use the inverse square law to get nice, dark backgrounds. I love this type of background because it leads to simple images, it hides my messy house, and it helps my subject really pop against a dark background.
The inverse square law has to do with light fall-off. The farther you are from the light source, the more fall-off you will have. However, the exact amount of fall-off is not really intuitive.
The quantity of light will be inversely proportional to its distance.
According to the law, the power of the light will be inversely proportional to the square of the distance. Therefore, an object that is twice the distance from a source of light will receive a quarter of the illumination (not half, as you might expect). Photographers who use artificial light need to understand this law to appropriately light their subjects. However, as natural light photographers we can use our knowledge of this law to perfect a technique for getting simple, dark backgrounds. We can utilize this law indoors, in our garage, and even outdoors.
If you want, you can ignore the boring math, but remember: the key to this technique is light fall-off. Light falls off increasingly over distance away from our light source.
Garage light is actually amazing for photos with black backgrounds. Don’t worry – your garage does not need to be neat and tidy! You want to place your subject in the shade but close to the line from the sun. So look for the line on your garage floor of where the light and shadow meet. Place your subject right inside the shade. Try a chair if you have a subject that moves constantly like mine do! (Bonus tip – I actually used a tricycle for this image below and let her sit on it!)
By placing your subject this way, you get nice light on their face, but the light falls off quickly and becomes very dark behind your subject. If it’s overcast or the sun is behind your house, you can simply place your subject right at the edge of where your garage meets your driveway.
The inverse square law works indoors as well. Look for an area close to a bright light source, like a window, that has a darker background (no other lights or windows in the background). Hallways are one of my favorite places to look for light like this. In my house I have a couple hallways where I can close off doors to block light except for one window.
You want to get your subject in the light from your window and expose for their skin. That way, the light will fall off into darkness behind them.
You can even use the inverse square law outside. Look for a spot that is in the shade, and has a dark background. The edge of woods works perfectly for this. In my backyard I have an open area and then some trees. I can place my subject in the shade, near the open area, with the trees behind her. The dark trees give a shady background, but I still get nice light on her face since she is near and facing the open area.
A few other tips for perfecting the black background look: shoot pretty wide open (think in the f/1.4 – 2.5 range) and get pretty close to your subject. You want to create nice depth in your images to achieve this effect.
This type of photo often needs a little help in post processing to get a perfectly dark background. I use mostly Lightroom for my editing, so I will start by lowering shadows all the way down. Then, if I still have any spots, I try using an adjustment brush and bringing down shadows and/or blacks in any areas that need to be darkened. If the photo still needs more work, I will try an adjustment brush with lowered exposure, and that usually does the trick! The healing brush tool in Photoshop is also great for removing any random bright spots. Sometimes I don’t stress about getting the background completely black – especially if I have white doors in my background.
Next time you’re looking around your house for interesting light, keep the inverse square law in mind! It can help you transform a snapshot into a more artistic portrait. And remember, this technique can be applied easily in your messy garage or even outside as well!
Want to learn more from me (and see how I edited some of the photos above)? Come join me in my Breakout Up Close and Personal: artistically capturing the details and emotion of everyday! It’s open now and until the 25th 🙂