First Principles of Light: How the distance of your light source influences the softness of shadows

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Welcome to the first in a series of the principles of light.  In the next few bog posts, I’m going to be teaching the basic principles of light – why light works, how it works, and how you can use light to your advantage.  In this blog post, I said that we light for four reasons: illumination, contrast, dimension, attention.  Light is a creative tool in your arsenal, and if you know how to use light, it can be used to tell the story the way you want to tell it.

This blog post today is probably the most basic element of lighting, but also, the most counter-intuitive.  Your knee-jerk reaction would say “but it does not make sense!” but in a later post, I’ll be proving the science that makes this possible.

So, without further ado, this post is how to control the softness/harshness of your shadow by using distance.

Herewith the premise: the closer your light source to your subject, the softer your shadow becomes.  The further your light source is form your subject, the harder it becomes.

Say what? Surely you got this the wrong way round?  This is why I said it seems counter intuitive – “logic” says that a closer your light is, the “more” light there is, thus it’s a harsher light, with harsher shadows, right?  Wrong.

Allow me to prove it.  I’ve got here a very simple setup – a Styrofoam ball, a white reflector to throw a shadow on, and a light source.  The light modifier was a beauty dish with a grid, simply because it is the most “directional” light I have with the least amount of spill, it it will demonstrate the principle the best.

I want you to take note here of the shadow the ball casts on the reflector.

We start off with the light at six meters away.  Notice how we can clearly see the shadow of the ball – and the light stand it is on – that is cast on the background.

Light Source Six Meters Away

Light Source Six Meters Away

Next one up, I halved the distance, to three meters.  (Tech note:  the first thing that happens here is we have “more” light.  So we will over expose the ball – I needed to close my aperture to “normalise” the exposure.  I could also have turned my light intensity down – either would have given the exact same result at the end of the day.  The aperture and/or intensity of the light affects the exposure, not the quality of the shadow!) – here we can see the shadow going a bit more fuzzy.

Light Source Three Meters Away

Light Source Three Meters Away

At one and a half meters, halving the distance again, we can see the light source coming into the picture.  The light stand’s shadow is seriously fading out.

Light Source One and a Half Meters Away

Light Source One and a Half Meters Away

At seventy five centimetres, we have about a ghost of a shadow left on our white background

Light Source Seventy Five Centimeters Away

Light Source Seventy Five Centimeters Away

And at “as close as I could get it without the light stands falling over”, the shadow completely disappears!

Light source as close as I could get it!

Light source as close as I could get it!

So, basic proof that the closer the light, the softer the shadow.

But that is for a “cast” shadow, what about the “light side” and “dark side” of the object?  Well, herewith two close-ups of the ball itself.  Astronomers call the line where light and shadows meet on the earth surface the “terminator”. So, let us look on the terminator on the balls here. On the left, we have the light at 6 meters.  (I had to get my aperture down to f/3.5 here to get the right exposure, which is why the depth of field is so low).  We can clearly see the line of the terminator, giving us a “harder” shadow.  On the right, we have the light very close to our subject, and the terminator is a lot more “gradual”.

"Far" versus "Close" Terminator Lines

“Far” versus “Close” Terminator Lines

Thus, the first principle of controlling the “look” of your photo:  How hard to you want your shadow?  Do you need to put your light close, for a soft light, or far away, for a hard one?  There is no right and wrong – its purely application.

Next time: how the size of your light also influences the softness/hardness of your light and shadow!

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On Tuesday August 30 2016
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2 Responses to First Principles of Light: How the distance of your light source influences the softness of shadows

  1. Debbie Boettcher says:

    Fascinating!

  2. […] that is the theory, anyway.  But there is a spanner in the works here…  as I demonstrated in this post, moving a light further away, makes shadows harder, and hard shadows can be unpleasant.  A hard […]

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