How light works?
How light works? | ||
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Photography is all about light—light bouncing off pigments and dyes, light shining through gels and filters, and the shadows and depth that come with the absence of light. Light is one of the basic influences in life. In fact, it brings life. Without light there would be no energy on the planet except that lurking deep in its bowels. And yet we're not exactly sure what light is. The scientific answers at times contradict each other, and if you start to peer at it too closely, the physical nature of the universe develops cracks. So we're not going to do that, but we will look at it in less intimate terms. Light is a form of energy. It is just a small segment of the vast energy that fills the universe in the form of the electromagnetic spectrum. Energy moves through space as waves. The distance from the peak of one wave to the peak of the next is the wavelength, which determines many of the characteristics of a particular form of energy. The only energy we can see is a narrow band of wavelengths in the middle of the spectrum. We call this band light. We sense other wavelengths in the form of heat, and we've created various devices that detect energy with wavelengths longer than those of light—infrared—and shorter wavelengths, such as ultraviolet. The wave characteristics of the spectrum account for several useful aspects. Waveforms give energy size and shape. Microwaves are blocked by the screen filled with small holes in the window of a microwave oven because the waves are too large to pass through the holes. Light, however, is small enough to pass through easily. Light can also take the form of a particle. Each particle carries a specific amount of energy. This is useful when measuring light, as we do with light meters. A meter essentially counts the number of particles that strike a light- sensitive surface. The amount of energy in a light particle is related to the light's wavelength. The shorter the wavelength, the more energy the wave contains. (Most of us would probably say a yellow or red light is warmer, but a blue light actually packs more energy.) The energy levels of different colors of light are not so different as to be a concern—or use—in photography. Light spreads as it travels, like the ripple on a pond. If light passes through a hole or past the edge of some obstacle, it will spread out from those points. The waves of light are not perfectly in step. The peaks of some waves will meet the troughs of other waves, with the effect that they cancel each other out, producing a diffraction pattern. This accounts for the fact that spotlights and flashlight beams do not produce perfectly smooth circles of light. As light waves spread, the energy originally contained in the light becomes weaker because it's spread thinner over a larger area. In photography, this is particularly significant because an object 5 feet away, being photographed with a flash, is four times as brightly lit as the same object 10 feet away. | ||