Learning about lighting in Photography...the science behind light

If you think about it, the only thing we're doing when we're taking photographs is capturing information about the light entering the lens. Most of the time, it's a reflection of what is in front of the camera.

Compared to our eyes, cameras have very poor vision. They are only able to "see" well in a limited brightness of light. I've heard that our eyes are able to see in what would be considered a 10 f-stop range, but our cameras can only see about 4 F-Stops worth of light. So light is the most crucial aspect of photography.

Dollar for dollar, it pays to spend more money on your lighting than on your camera equipment. Expensive camera gear is like buying a lawn mower. You can go cheap and buy a push-mower, but it will take you longer to mow the lawn. In the same way, cheaper cameras can do a lot of what more expensive cameras can do, but the more expensive cameras will make things easier. At any rate, you get more bang for your dollars out of better lighting.

What is light?

Light is a type of electromagnetic radiation that is caused by photons emmitted by a light source and transmitted through a medium or reflected by a medium. The fields change strength and fluctuate like a wave. How often these waves fluctuate in strength s called the frequency of the waves. You see different frequencies of light as colors. Blue light, for example has a higher frequency than red light.

If you're familiar with how sound works, then thinking of light is similar. With sound, different frequencies are heard as different pitches, The amplitude (how big the waves are) are heard as volume. With light, the amplitudes are viewed as brightness and the frequency as color. Like with sound, there is only a certain range of frequencies our eyes are capable of seeing. We call this range visible light.

Brightness

Visibly, we see the effects of light on objects as brightness, color and contrast. Of these three, brightness is the most important component. As a matter of fact, without a certain level of brightness, our eyes are unable to see color very well.

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Technically, we see the effects of light as brightness, color and contrast. The brightness refers to the intensity of the light, the color to the hue of the light source and the contrast can be seen in the harshness of the shadows.
© Ray Villalobos 2009

Our retina contains two types of photo sensitive receptors...cone shaped and rod shaped. The rod shaped receptors are responsible for recording changes in brightness or value, while the cone shaped receptors record color information. There are 20 times more rod shaped receptors than cone shaped receptors. Therefore, your eyes are much more sensitive to brighness than to color. Which explains why it's difficult to tell the color of an object at night.

In photography, a brighter light is always a better light. A brighter light will give you the ability to shoot at faster shutter speeds to freeze motion, lower ISO's (to reduce graininess) and allow you have more flexibility with your F-Stops. Dimmer lights means sacrifices have to be made. This is why flashes exist, to create more light for your photographs. Thankfully, the sun is a very bright light so for a lot of photographs if you can harness it's power it will allow you to capture great photographs.

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A brighter light gives you more flexibility in your shooting. You can use higher ISOs, faster shutter speeds, and more varied F-Stops. My studio's four light setup gives me a lot of flexibility in shooting both people and objects.
© Ray Villalobos 2009

Color

Light traveling at different wavelenghts is interpreted by our eyes as having different colors because it is traveling at different wavelengths. This is why cameras have to make a white balance adjustment in some photographs. A flourescent light source will have a green tint, while a tungsten light source will have a yellow tint. If you've ever gotten a picture that was too yellow, you know what I'm talking about. So your light source itself may have a color and affect how other colors are interpreted by your camera.

Contrast

Another property of how we see light is how much contrast the light creates in a subject. We see this as the "harshness" of the light. High Noon sunlight on a cloudless day is very harsh and creates shadows with a lot of contrast. A cloudy day creates a light that has very low contrast.

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The contrast in a photo is caused by the orientation of the angles hitting the subject. The contrast is most visible in the shadows cast by a subject.
© Ray Villalobos 2009

The contrast is caused by the light hitting an object at certain angles. If a light hits an object with similar angles, the light has very high contrast. If a light hits objects at different angles it has low contrast. A low contrast light is considered a softer, more pleasing light. The best way to see the contrast of a light source is by looking at it's shadows. A high contrast light source casts hard edged shadows. A low contrast light source casts soft, diffused shadows.

The physical size of the light source is not really relevant here, it's it's apparent size in relationship to the object it's lighting. The sun is so large that you could fit more than one million earths inside it (865,000 miles in diameter), but even though it's huge, it's more than 92 million miles away so it appears small. The moon, which is much closer appears to be the same size as the sun (making solar eclipses possible) even though the sun is 400 times as far away. So the moon "appears" to be the same size as the sun because of it's position. To make a light source appear bigger, you can bring it in closer.

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The relative size of a light source is more important than it's physical size. The moon appears to be about the same size of the sun because the sun is 400 times farther away from the earth. This makes total solar eclipses possible.
© Ray Villalobos 2009

So, one way you can control the harshness of your shadows is to change the position of your light source. If you bring the light source closer, you'll have a softer light. A lamp that is brought very close to an object can look to the object as a bigger, softer light source.

You can also make a light harder by putting something that focuses the light rays emanating from it. Photographers do this with grids or snoots. A snoot restricts the angles from where light comes from. A grid is an attachment that makes the light coming from an object appear to come from less angles.

You can also make the light appear to be bigger by using a diffuser. A diffuser is like clouds, they scatter the angles of a light source and make it softer. Because of this the apparent size of the light source will be bigger. In reality, the subject being lit will no longer be light by the original small and harsh light source, it will now be lit by the softer diffuser. This is why you'll see a lot of photographers point their flashes up when taking a photo indoors. They are using he ceiling as a diffuser and lighting the objects with the larger ceiling, not with the flash.

Transmission

Different objects can change as it passes through them. When light is able to pass through an object, the object is said to transmit light. Air and clear class are good examples of objects that transmit light. But they don't do so perfectly. This is why we appear to have blue skies in daylight. The particles in the atmosphere absorb some of the light coming from the sun and reflect it in the shorter blue wavelenths. When the sun is close to the horizon, the light from it takes longer to reach you and therefore appears weaker and changes color. Outer space looks black because there is no atmosphere to absorb the light waves from the sun. An object that perfectly transmits light would be invisible.

Refraction and the speed of light

Refraction happens when an object causes light coming through it to change speed. When light goes through an object, the object can slow down the speed of light temporarily as it passes throught he object. You can see this very clearly by putting a long object partially in a class of water. The object in the water seems to bend. Refraction is almost non-existant throug the air, but it's very apparent in glass and other objects. As a matter of fact, refraction in camera lenses is one of the things that make photography possible. It's also the reason we can see and photograph glass objects. A lot of times what you see is the refraction caused by the glass material.

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You can see refraction clearly by looking at objects partially submerged in a glass of water. The light slows down temporarily as it passes through an object and then speeds up once it passes through the object.
© Ray Villalobos 2009

Diffusers

Certain objects are said to be transluscent as opposed to transparent. Transluscent objects cause light going through them to become scattered and appear to come from different angles. This is really important in photography because a diffused light source can appear to be a much larger light source.

If you've ever used a laptop, you are familiar with a diffused light source. LCD's are not cabable of producing light so they are usually lit with a flourescent tube on one edge and a diffuser material that spreads out the light evenly throughout the monitor.

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Translucent objects diffuse light...scatter light so that it goes in different directions. This iPod was underlit with a translucent diffusing colored materials. It's technically acting as a colored gel.
© Ray Villalobos 2009

You can diffuse light from a light source not only with transparent objects; reflective objects can also diffuse and scatter light. This depends a lot on the material and roughness of the subject.

Absorption, Reflection and Color

Most of the color we see in objects is reflected colors. Objects in the environment absorb certain wavelengths of light and reflect others. What we see as color is the result of an object absorbing certain wavelengths and reflecting others. A white object reflects most of the wavelengths, a black object absorbs most of them. A mirror reflects most of the colors directly with very little diffusion. Even though a white object reflects most of the wavelengths from light, it doesn't do so evenly. White objects also diffuse a lot of the light. White objects are excellent diffusers because they don't change the color of the light, but do scatter the angles and diffuse the light making it appear to be bigger and softer.

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