Monday, March 15, 2010

The Nature of Light

It's Monday! Thought I'd start the week off with a boring physics lesson. Why not? Physics is an integral part of photography's art.

Here goes:

Light is a naturally occurring, transverse, electromagnetic wave that can be seen by humans and other species.

Light is produced two ways: 1) Incandescence, i.e., the emission of light from "hot" matter and 2) Luminescence, that is, the emission of light when excited electrons fall to lower energy levels. (Luminescent light occurs in matter that may or may not be "hot.")

Light is fast. Real fast! Galileo tried to figure out the speed of light but couldn't: "I have tried the experiment only at a short distance, less than a mile, from which I have not been able to ascertain with certainty whether the appearance of the opposite light was instantaneous or not; but if not instantaneous it is extraordinarily rapid."

We now know, of course, that light travels at 299,792,458 meters per second. (In a vacuum.) For all intents and purposes, leastwise for most people's photography, it might as well be instantaneous.

Intensity is the absolute measure of a light wave's power density. Brightness is the relative intensity as perceived by the average human eye.

Most light is polychromatic. There are exceptions. A laser, for example, can effectively produce monochromatic light.

There are many forms of light, e.g., infra-red, ultra-violet, but for our purposes visible light is the most important. It's how we see. It's what we capture and record on film or sensors.

It's fortunate the kind of photography most of us pursue, infra-red shooters aside, utilizes visible light. Yep! That's a good thing. It enables us to see what we're capturing or recording. BTW, we don't actually "capture" the light. We record it as it reflects and then interacts with various mediums like film emulsions or digital sensors.

As photographers, we manipulate light. We exploit it. We reflect it, diffuse it, and block it. We do this whether it's artificial light (technically, a contradiction in terms) or natural light.

When shooting using natural light, we look for places to shoot where the natural light, the light coming from our sun, is reflected, diffused, or blocked by things in our shooting environments and in ways that enhance, or make pretty, the light falling on our subjects and reflecting back on our recording mediums. We sometimes prefer to shoot when the light is angled or modified in aesthetically pleasing ways: Golden Hour and early morning sunlight are two such examples.

Also as photographers, we need to be observant, critical, examiners of light. To borrow from the religious-minded, we need to "see the light." I know that sounds overly simple and a somewhat redundant phrase. After all, if it weren't for light, we would not see anything at all. Still, far too many photographers don't seem to see the light, the good light, the best light, the cool light. I sometimes wonder if some photographers spend much time at all searching for it?

While it may seem that light is light, all light is not created equal. Leastwise, it doesn't appear equal. It certainly doesn't reflect and refract in equal ways. When it comes to photography, there is some light that is better than other light. Often times, far better.

Again, this stuff all sounds so simple.

But maybe it's not?

While this update might include more than you ever wanted to know about light, you are, as photographers, artists who use light instead of paint, pencil, chalk or pen. I think the more you know about light the better you can become as a light-painter, that is, the better you can become as a photographer.

The gratuitous eye candy at the top is Tori. Who knew a simple lesson in physics might also include a picture of a hot, sexy, half-naked babe? Betcha they didn't use visual aids like that one when you were in a high school or college physics class.


Don said...

Let's not forget the "color of light" which is constantly changing. I know that you mentioned "the Golden hour and early morning sunlight" The color temperature is different during these times, and renders differently on film and digital sensors. An awful lot of young photographers do not understand color temperature and how it affects their images.
here is an experiment for new photographers: Pick a scene that you think is really great to shoot. Set your camera on a tripod and shoot one shot at the top of the hour, every hour for as long as the light lasts. Keep your exposure settings balanced as the light changes. Don't change any other settings. At the end of the day, you will see that, although all photos were of the same thing, all photos will be different. Of course, those shots made between 11am and 3pm will look flat and ugly, but the others will have a richness of color and depth. You will notice that each of these shots will have a different "color cast". That is caused by the changing color of the light. Knowing when to shoot is as important as who and where.
The Photodawg

joshua said...

The Earth is approximately 24,901 miles around the equator. So, light would travel around the Earth 12,039 times in one a bed.

Anathaema said...

@joshua : your bed doesn't catch light :)

Anonymous said...

The speed of light is actually 299 792 458 meters per second.

EleganceAndChaos said...


Speaking of controlling light,
I know you use small umbrellas for your rim light sometimes. What brand are they and where did you get them from? I am using small 18" X 18" softboxes now, but like you I am getting lazy in my old age, especially on location. I have found some umbrellas as small at 30", but have you found smaller ones?

jimmyd said...


Oh yeah. You're right.Just fixed it. Thanks!

Orcatek said...

Another great read. Understanding light is so critical to creating great photography.

jimmyd said...


Hmm... they're not name-brand umbrellas. I think they're about 18" or maybe 24" and, for the most part, I only use them for some edge lighting from behind. I also have a small soft box about the size of the one you mentioned and sometimes use that as well.

jimmyd said...


An awful lot of young photographers don't seem to understand much other than photoshop. Just sayin.

MarcWPhoto said...

Trivia item: The speed of light is a defined constant. When you try to "measure the speed of light," what you are doing is measuring the distance between two points.

It is possible to do this with marshmallows in a microwave oven.

For real.