Pixapro Tips

Explaining the Inverse Square Law for Photography Lighting

For those using artificial photography and video lighting, the Inverse Square Law will apply to your lighting setups whether you realise it or not! While many photographers and gaffers are familiar with the ISL, here is our brief breakdown of how this works, to help you understand your lights and how you can leverage the science to benefit your photos and video content.

What is Inverse Square Law?

The Inverse Square Law is a way of measuring the light drop-off from a lighting source, such as a flash or LED. Most easily visualised by using LED lighting or a modelling lamp, light drop-off, in essence, covers how as light reaches further from the source and spreads out further, brightness decreases as the light doesn't reach as far.

Source: Jake Hicks Photography. Light drop off from a regular point of light strobe with reflector dish

In a straightfoward sense, the inverse square law means that if you double your distance from the source of your light, this then quadruples the area that your light will spread.

So, the light will appear disproportionately brighter if you stand right up close to to it, and will decrease in brightness dramatically just a few more steps away.

You can view this concept on a super small scale; just use your smartphone torch and hold it about 1 inch away from the palm of your hand. Move it 1 further inch away from your hand and see how much further the light spreads and how much softer it looks.

Image source: Wikipedia (a much better diagram than I could draw)

So what does this mean?

As a result of this, the further away your subject is placed from the lighting source, the softer the light will be, and the softer the shadows. Positioning your subject right up against the light will result in a small cast of light, with harsh shadows and hard lighting.

This effect, where objects further away from the light source are more in shadow, is described as "light fall-off", and different types of lights, paired with different modifiers, will impact this fall-off effect differently.

Jake Hicks has a detailed blog on the Inverse Square Law in relation to LED tubes and Panels (Specifically the Rainbow LED Tubes), and how the shape of these will impact light fall-off here: Lighting Setup: Affordable LED Tubes

Why does Inverse Square Law matter in Photography?

Quite simply, as ISL impacts how your lighting and shadows fall, this therefore impacts the result of your image. A harsh, dark shadow will often evoke a more dramatic, striking result, and is good for things like character portraits.

Images by Gavin Hoey at The Photography Show 2022 with Chloe Kerley. The result of Inverse Square Law in action - the left image uses close-up light and produces harsh, contrasted shadow. The right image has more distance between Chloe & the light, making the shadows softer and less overpowering.

Putting your light further away and making it softer results in a wider, more diffused quality of light with softer shadows, and is better for things like family portraits, beauty portraits and more. Softer shadows are reminiscent of natural sunlight and so are more natural to the human eye and well-suited to non-dramatic, natural images.

The distance of light will affect shadows in a few different ways. It can soften shadows and make them less contrasted, but it can also feather shadows. Meaning that the edges of shadows will appear less sharp and more blurred.

How to use Inverse Square Law in your Work

As a result of how ISL works, you can actually use it to your advantage when lighting images or video. If you're limited on modifier options but need a softer quality of light, you can simply use your light bare-bulb, and move your light further away from your subject to make the effect seem diffused. Generally, you might need a light with a bit more power output however, to be able to reach far enough and provide the light needed.

Another example of Inverse Square Law using Godox TL120 RGB LED Tubes! See how the light tube produces bright, harsh light when held next to Chloe's face, but demonstrates dramatic light fall-off the further it has to reach. Taken by Gavin Hoey at TPS 2022.

If shooting with multiple subjects, Inverse Square Law can also result in your light putting the subject further from it in more shadow than the subject closer to it, particularly if your light is quite close-up. To make the shadows look more even, simply move your light further away.

Try it yourself!

Give it a go yourself at home and see what kind of results you can create by playing with the distance between your light and subject! Getting familiar with the concept makes it easier for you to adapt your lighting on the fly when on a shoot.

When using a proper lighting setup, try adapting your light effect, and adding or removing modifiers to see what difference this makes.

Browse Lighting Modifiers

While you can go more in-depth on how ISL works, this is the important information you need for it directly impacting your photo and video lighting, without the nitty gritty of the physics and maths behind it.

For more photography lighting FAQs and guides, check out our blog page, or search in the product search bar above. www.essentialphoto.co.uk/blogs/news