Always failed in physics. Big way. Reason being that no one took the liberty to remind me that physics has something to do with photography. Which would have sparked my interest. Most likely. Possibly. Really. Like in: Really-Really.
The picture above is a good example of physics in action. In this case it is the "dramatic" light falloff I'd like to draw your attention to. Of course, a similar effect can be achieved in Photoshop with very little effort by some virtual vignetting. However, photographers that revert to mighty Adobe all the time should not whine too much when it comes to payments and budgets. The one who says "I'll fix that later in post" once too often risks his professional standing and consequently value towards clients. Less value translates into smaller budgets. Or simply no budgets at all.
And it's the same with physics. It's simple. Predictable. The light falloff is explained by the inverse square law of light. It says that intensity is inversely proportional to the square of the distance from the source of that physical quantity. See? I've lost ya' already. In other words: Get your light as close to your subject as you can and the falloff will be all yours. Put your light away from your subject and your contrasts will be more moderate. It is the same principle that lets you turn a white background into black - given you have enough room to maneuver. Or any other shade of grey (whoohoo!) you may desire, young master photographer.
The light source in the shot above was very close to wonderful Wiebke's head. The reflection in her eyes is giving away its position and - to some extent – its distance to the subject. A small silver Elinchrom beauty-dish, feathered, gridded, on a boom. The light hits her forehead at full steam, but by the time it reaches her shoulders it already has lost at least a full stop. The white floor has turned pitch black. Due to the falloff, her face and cheekbones are perfectly contoured; almost like chiseling with light.
Here is another shot, same model, same studio, same modifier but a more conventional setup in terms of light direction and distance. Less contrast, less drama – and all that by just changing the distances: source-to-subject and also source-to-background. The light source now being farther away is illuminating both the subject and the background more evenly.
Distance is what makes the difference. And some strategic feathering. And the deliberate use of ND filters to keep the DOF small – especially when your light source is getting extremely close to the subject.
See, I told you it was simple. And lighting is all about control and physics. Once you've nailed this it is only a small step to rocket-science. And, at some point, maybe a giant leap for mankind.