Understanding Light Falloff

Understanding Light Falloff

If you read my blogs it won’t come as a surprise that I’m particularly interested in off-camera flash, especially for lifestyle portraits.

I have been experimenting with Speedlight’s over the last few years, which has dramatically improved my photography and my understanding of light and lighting, but I am far from being an expert and continue to hit hurdles in relation to lighting. Understanding light, natural or artificial is integral to photography and can make a huge impact on an image.

Many aspects of photography take time to learn and improve and in my opinion, lighting is perhaps the most challenging to master. However, by practicing, one gains experience and you are the able to start to learn what you did not know.

The importance of understanding light falloff can have immense practical implications for photographers, but when you start out on your flash lighting journey, Inverse Square Law examples (Distance = 2. Inverse = 1/2. Squared = 1/2 x 1/2 = 1/4) for me was more of hindrance than a learning point and I just did not understand what I was reading.

In this article I will be sharing the important principle of light – Light fall-off, in a visual way that I hope will make the basic principles of Inverse Square Law easier to grasp.

One of the best ways to begin to understand Inverse Square Law and how it works is to take some images with your flash against a wall. The two images below were taken with a Godox TT350 flash, zoom head set at 24mm and the same TT350 flash, with the zoom head set at 105mm. You can see clearly the difference in both light falloff and spread (angle of the light)



Whenever we use a light source to illuminate an object, that object is being hit with multiple “rays” of light. Some of those rays are hitting the object in the place which is nearest to the light source, and some of the rays are hitting the subject where is furthest from the light source.

The light that falls on the closer side to the light source will be brighter then the light hitting the furthest side. This is because the light will scatter more when it makes its long journey to the far side. (This is not true for focused beams and laser, but this thumb rule can be applied to most studio lights and strobes).

In portraiture, when you are taking a portrait using only a key light (i.e. a single light). Your subject will be more lit where the light is close and darker where the light is far.

Example Of Godox AD200 Bare Bulb with Normal & Wide Reflector



What Effects Light Falloff?

The distance of light from the subject
the closest the light source is to the subject, the stronger light falloff you’ll get.

The Size Of Light:
The larger the light source the more diffused the light it produces and the less light falloff you will experience. For example, a large softbox will produce less light falloff then a small softbox; a bare flash will produce more light falloff then a flash shot through an umbrella.

The further one takes the light source from the object being lit, the less light fall of one can expect.

How far should you place the light source? That depends on your lighting vision, but here are some considerations:

The furthest the light the less light falloff and less drama.

If you increase the distance of the light source from your subject the light is getting “smaller” and harsher. The effect will be more noticeable if you are using a smaller softbox.

Experiment with the light falloff, you’ll be surprised how effective and useful it can be in photography.

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