The use and manipulation of light in photography can be simplyfied into four parameters with only a few basic rules. If you master those and get your head around them entirely, you can master any lighting situation you can dream of, be it a large set of studio strobes you have to handle, or lighting with the help of dinner plates and trays as light modifiers. The following applies to any kind of light and any situation.
We humans have two eyes to look at the world. This enables us to see things in 3D, to orient in space and to position things in relation to oneanother. We are used to this.
Now with photography, we remove one dimension. An image is only 2-dimensional, left-right and up-down. Still we are trying to determine a sense of space in a picture. We automatically look for clues of dimension and space, we are programmed to do so. If we give that to the viewer, he or she will feel comfortable, will be interested and will start exploring all dimensions of the image.
The question is: how do we create that third dimension back into the image. Besides the possibility of depth of field, we use light, or shadow, to be precise, to do just that.
Lets look at how we can control light to create shadows and depth.
Characteristics of Light
There are only a few characteristics of light:
- Direction
- Color
- Hardness / specularity
- Brightness / intensity
Direction of Light
It is fairly easy to control the first two:
Light wants to go everywhere (as long as its not a laser). To control the direction of the light, just cut it off from where you don’t want it to go. There are light shaping tools, barn doors, gobos, cutters and flags to do that, just to name a few. We position the light and tell it where not to go, and we are all set.
Color of Light
Light is electromagnetic waves (some scientists argue with that, but we’ll stick with it for now) with a wavelength of 400nm to 700nm (nanometers), where 400nm would be blue/purple and 700nm would be red. Below 400nm is ultra violet, above 700nm is infrared, both not visible to the human eye.
The color in photography lighting is primarily controled by gels, which basically just filters out all but that light desired. It can also be influenced by the brightness, i.e. when dimming the light.
We measure color temperature (notice the word temperature here) in Kelvin, which is a unit for temperature. It gives the color a material would have and glow with if heated up to the respective temperature.
Note that studio and compact flashes usually can change intensity without changing color temperature. We can also change and adjust the overall color with our whitebalance settings.
Hardness of Light / Specularity
Another characteristic of light is its hardness, as seen on the shadows subjects create.
The rule in short:
The larger the relative size of your light source in relation to your subject, the softer the light, the smaller the relative size of your light source in relation to your subject, the harder the light.
The sun in the sky is a very big light source (a few million miles diameter) but it is very far away. Shadows in direct sunlight are hard and edgy. Now if we have a cloudy day, the clouds become our light source. That lightsource is now very large and very close, so we get soft shadows or no shadows at all.
This video by Mark Wallace illustrates that very well:
Now lets look at that in a controlled environment.
We can see two things happening:
- If the light source is closer to the subject (the exposure on subject A is constant) the background will be darker. If we move away, the subject-to-background lighting ratio is more homogenous, the background is illuminated more evenly, but we need more power from the light source. (important for small battery powered light sources)
- The larger the light source (bare bulb and an umbrella in this example), the softer the shadows.
In a real-world-example, let’s say we want to take a beauty-portrait of a model with very soft lighting on a white background we want to have appear as grey, we would then use a small softbox. If we now wanted to take a full-length-portrait of that model and wanted the same quality and softness of the light, we would have to
- use a bigger softbox to cover the full body
- adjust the distance of the light in relation to the model for the same softness, which means move the light away
- move the model and the light farther away from the background, as a greater distance between the light source and the model would result in a brighter background.
Which is where we come to the…
Inverse Square Law
Now let’s look at the final one, lets change the intensity of the light.
In the most simple setting, you can just dial down your power source to reduce the power. You can also increase the distance between the subject and the light. As long as we are only looking at the brightness of that one subject, we are perfectly fine, and in no trouble. The trouble does start though, as soon as we introduce a second subject, be it a second person in a group shot, or just a background. Now we also have to control the light hitting that second subject or background (we will use a background for easier explanation here).
What we have to take into account is the effects of the inverse square law. Is states that the light output from a source reduces to the second power in relation to the distance from the light.
In physics, an inverse-square law is any physical law stating that some physical quantity or strength is inversely proportional to the square of the distance from the source of that physical quantity. (Wikipedia)
Put simply: If we double the distance from the light, we have to have four times the power to have the same amount of light hitting the subject.
Lets look at that in a practical example. In the image below we can see the light output in f-stops at the varying distances.
The important thing to note is the light fall-off and the size of the areas of roughly the same amount of light or exposure.
- If we position subject A at position 1 and a subject B aproximately 30cm behind that subject at position 2, that subject B would be one stop darker than subject A. Subject B would be hit by half the amount of light hitting subject B
- If we position subject A at position 1 and a subject B aproximately 100cm behind that subject at position 4, that subject B would be two stops darker than subject A. That would be very dark compared to the correctly exposed subject A. Subject B would be hit by one quarter of the amount of light hitting subject B
- If we position subject A at position 5 and a subject B aproximately 100cm behind that subject at position 8, that subject B would be probably two-thirds of a stop darker than subject A. In a group shot, that could be acceptable, or we could move even further away to position 8, 9, 10 etc. where eventually subject A and B would have the same exposure at a distance of 100cm.
If we think about subject B as a white background (or cream in this example), the background would be a very dark grey in example two (below left), and still a bright grey in example three (below right).
Lets look at the settings:
- The camera was set to ISO 100, f16 at 1/200th of a second for both shots.
- The distance beween the subject and the light has been doubled for the second shot.
- Flashpower is set to 1/16th in the first shot, and 1/4th in the second shot (or +2 stops).
As we can see, the exposure on the subject is identical, only the background (subject B) changed and we needed a lot more flash power in the image.
This is the way to control the brightness of a white background from white to completely black. All you need is a powerfull strobe and a lot of space behind the subject to achieve that.
Happy shooting!
Related info: DSLR, Shutter Speed, Aperture.
Also check out this article here!
I will be happy to help with any questions you leave in the comments section.
