Hardness of light

By Oleg Ti,   January 10, 2013,   Views: 6783,   Comments:

 

     

Look at these two photos where this battered but still elegant C Stand works as a “model”.

On the left picture you can see such a soft, feathered shadow which could be hardly seen, in spite of short distance of the C  standing by the wall. On the right photo - the well drawn shadow with well-shaped edge. We can definitely declare that the light on the left picture is soft, and is hard on the right photo. And if to say about hardness of the light, these two photos significantly distant from each other.

Now try to imagine that the left picture was taken with standard reflector which we usually consider as a very hard source of light which we use in the studio to get very deep shadow with sharp edge. But the right picture was made with the soft box, with the modifier we want a photo with soft, blurry shadows, with smooth and hardly visible gradients.

It's hard to believe but it is true!

To get the left picture I used 12 inches (30cm) reflector which is slightly wider than the standard reflector, the right picture was taken by 30" 30" (75cm x 75 cm) soft box. Why we got so unpredictable outcome?

To make these photos, I used  both modifiers that are located at different distances from the object: on the left picture the standard reflector is located very close to the object, but on the right the soft box is moved to the opposite corner of the studio to get few meters of distance of the C Stand. 

The soft light with reflector and the hard light with soft box, breaking almost fundamental rule of lighting thus breaking the rule of thumb. To understand this, let's give a definition of the hardness and the softness of light.

The soft light produces diffuse shadows with soft edges and the hard light a very contrast shadows with sharp edges.  It is from to the light itself, not the source of light (i.e. softbox etc). You will get the most soft light if you get a big modifier like a big soft box or umbrella.

The softness (or hardness) of light depends also on the distance between the lighting source and the object. The closer the source, the softer the light becomes. And vice versa the further the distance, the harder the light. Therefore, to determine the hardness of light in addition to the size of the lighting source ,we have to remember another value - the distance to the object.

You can easily compare the difference of the two pictures with the different lighting techniques.

We could say that the softness (or the hardness) of light is the coefficient which is defined by the area of the surface of lighting source in relation to the distance to the object.

I will operate not with area of the surface of source but with lengths of the sides of source's modifier. Why we shouldn't use the area? Because the modifiers canot have a  round or square shape. For example in case of using stripbox we can get different degrees of hardness in different planes. Stripbox placed vertically gives soft light in the vertical plane, and quite hard in the horizontal and we can change this situation just rotating 90 degrees: in the vertical plane it will be hard and in the horizontal will be soft.

But let’s get  back to our devices:

The standard reflector on the left picture has diameter of 30 centimetres and is located in only 15 centimetres from the object. Lets divide 30 by 15 and get coefficient of softness of 2. It means that the light is quite soft.

On the right image I used square soft box with 75 cm sides moving to 7,5 meters distance from the C Stand. Dividing 75 cm by 750 cm (7.5 meters) I get 0.1 softness coefficient. It identifies the hard light.

What could happen if they change places?

It we moved the softbox to the distance of 15 cm we the coefficient would become 5. This is the almost completely soft light and you could hardly see shadow and edges behind the object.

Reflector, moved to 7.5 meters distance, would give the coefficient 0.04. The light would be extremely hard to resemble the sun light and we could see strong shadow with harsh edge.

Now lets solve another dilemma:

How far should the reflector be to get the same hardness of light as we get on the picture with the soft box lighting?

We have to use the coefficient 0.1 to get the same hardness of light. Lets divide the diameter of the reflector by this coefficient and we obtain the value of 3 meters (300 cm). 30 cm divided by 0.1 = 300 cm

In an  opposite situation, How close is it necessarily to move the soft box to get the same softness of light that we get with reflector on the left picture?

If we divide 75 cm (length of the sides of the soft box) by coefficient 2 (as on the left picture) we get 37.5 cm. It shows us the distance we have to use between the soft box and the C-Stand to get the same softness as on the left picture.

I hope this little experiment with a mix of Algebra equations will help you understand the nature of the softness of light. The different capabilities you can do by possibilities changing position of light and using different types of sources.

You can understand that there are objects that get soft or hard light from those sources. Any light source can becomes soft (to nearby objects) and hard (in relation to distant objects).

And at the end let's calculate the hardness of sunlight. 

Diameter of the Sun is 695 900 km. The distance between The Sun and The Earth is 149.6 million km. Let's divide the diameter to the distance and get around 0.005. Very impressive value! Very hard light!

Now take a standard reflector which usually has 20 cm diameter.

How far should it be moved from the object to get the same hardness of light equal the solar light?

Lets divide 20 cm by 0,005 and we are getiing 4000 centimetres i.e. 40 meters. Hardly anyone would move the reflector to such a huge distance, but we (at least in theory) know what needs to be done to achieve the same hardness of light as we get from the Sun.

We could discuss the "beauty", "aesthetics" of light of various sources but sometimes we should simply use the numbers to deal with one of the most visible features of the light we use in the studio. But we have to remember that this is not only one feature of light we encounter with in the studio.

I guess that will be our next lesson.. 

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