Intensity of Light

Intensity of Light

Characteristics of Light

 

In the previous articles of this series we had a look at the quality of light in terms of contrast but also of hardness and softness of light, the color temperature of light and the direction of light. Today’s article is all about the fifth characteristic of light, its intensity.

What does the intensity of light mean?

The intensity of light means merely how bright a light source is. There are light sources with pretty much every level of brightness that you can imagine. The brightest one would be direct sunlight, but then there are dimmable lambs, the moon (which is brighter than one would think it is), the stars, sunlight on a clouded day or natural light during a thunderstorm.

How bright a light source appears to be is not only depending on the light source itself. It also depends on its distance to the subject. A pocket light close to your subject might seem bright, while the same lamp in some distance to your subject might not seem bright at all. Your camera’s flash close to your subject might seem bright, but try to lighten up an arena with it, and it is suddenly not bright enough.
There is something called inverse-square-law. This “law” says that doubling the distance between any light source and the subject it is lighting up makes it appear only 1/4 bright. What does that mean?

Say you have a pocket lamp placed 1 meter from your subject. It lights up your subject with 100 Lumen. If you now placed the pocket lamp 2 meters from your subject, the very same subject would only receive 25 Lumen (1/4 of 100 = 25). If you, however, placed the pocket lamp half a meter from your subject it would be lid up by 400 Lumen.

How can we influence the intensity of light?

With artificial light sources

As you saw above, you can influence the brightness of a light source by changing the distance to the subject it is lighting up. Changing the brightness of a light source is easy to do for most artificial light sources.

Then, of course, there are dimmable lamps, where you only have to turn a screw to either make it brighter or dimmer. Your camera’s flash can change its brightness if you adjust a single setting to do so.

However, what happens really with that inverse-square-law? It has a little trick to it that we can use in photography. It states that the larger the area the light of a given source spreads across the dimmer the light gets.

Using diffusers

A diffuser helps you make a light source less bright. If you hold a diffuser in front of your flash, the directed light emitted from your flash becomes non-directed. This way it spreads across a larger area, without moving the flash into another position.
Of course, you could go and buy a diffuser from the next photo store, but you could also use a white bedsheet or curtain in front of your window.

A reflector lets you make a light source appear brighter, by reflecting light onto your subject. Areas, otherwise lost in the shades, can be brightened up with the help of a reflector.
Again, you could go and buy a reflector in a photo store (they often come as part of a 5 in 1 diffuser set). However, you could as good use white carton, aluminum foil or gold/silver craft-foil to create your own reflector.
If you are opting for a silver or gold reflector, it will not only add light to your subject, but it adds colored light to it. A gold reflector warms up the color of the light a tad, while a silver reflector warms it down a bit.

Examples

The next two photos are taken with the exact same settings for both the camera and the flash. The only difference between them is that for the second one I used a diffuser in front of the flash. Technically speaking I used two flashes: the pop-up flash on my camera to control the second, off-camera flash a little to the side of my camera and subject.

Teapot without diffuser high intensity of light
Teapot photographed without a diffuser

Teapot with diffuser low intensity of light
Teapot photographed with a diffuser

As you can see the second one, utilizing the diffuser, appears darker. Since the only difference between both photos is the use of the diffuser we can say that it has an influence on the brightness of the light source (flash).

With natural light sources

As we’ve seen, the distance between the subject and the light source changes the perceived brightness of the light source. With the sun and other natural light sources, this is, however, impossible to accomplish.

Also, the idea of using bedsheets to diffuse sunlight when photographing a waterfall seems rather strange. Sure you could try sewing all those bedsheets together and then maybe get them high up into the air with multiple drones. However, doing this might have you placed in a mental institution before you can capture any photo at all.
However, in small-scale, when you are photographing a flower or an insect, the diffuser technic can help.

So what can you do?

For a sunny day, the easiest would be to go out shortly after sunrise or just before sunset when it is not that bright outside.

If that is not an option, you could wait for a clouded day to get the advantage of using diffused light. Of course, while being on that once in a lifetime journey, you might not have the time to wait for the clouds to come. So what to do with that waterfall and all its burned out areas, which would look so good if only you could dim down the sun a tad?
You could try and photograph it as an HDR (High Dynamic Range), where you would take three or more exposures and combine them later in post-processing. Using one exposure to get the bright areas correctly exposed, one for the mid-tones and one for the shaded areas. However, since that is technically not changing the brightness of the light source, we’ll save HDR processing for a later article. 🙂

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