Module 2B: Properties and Quality of Light
B. Properties and Quality of light
Quality of Light
In the process of evaluating the light from natural and artificial light sources, the photographer also considers the quality of light. This includes the characteristics of hard light (specular) and soft light (diffused) but also the inherent color value of the light.
The Color of Light
The electromagnetic radiation spectrum includes a very small section that is visible to the human eye. This is known as the visible light spectrum. Visible light has varying wavelengths which determine how we see its color.
White light contains all of these wavelengths. Passing white light through a prism separates the light waves across the visible spectrum - simply put, a rainbow of color.
Refer to the abbreviation ROY G BIV. This mnemonic device helps us remember the order in which these light rays manifest themselves when white light is passed through the prism: Red, Orange, Yellow, Green, Blue, Indigo and Violet.
Color Temperature
Color temperatures describe the color values throughout the visible spectrum with a numeric value based on the Kelvin Color Temperature Scale. Color has a numerical value that can be expressed in degrees Kelvin or K°.
White Light
Take another look at ROY G BIV. If you think about the initials of Roy, you get R.G.B. (Red, Green, Blue). This helps us to remember that our cameras reproduce colors by adding values of red, green, and blue.
White light is the basis for the natural color we perceive in daytime sunlight. Daylight is White Light. We generally accept that it is measured as 5500 K°. On a camera’s white balance settings, daylight is represented by the sun icon.
The perception of color is the result of light reflecting off of a surface. Under white light conditions (5500 K°), color is how our eye interprets it; a white sheet of paper is white.
So, what happens when we view color under conditions other than white light?
Color Shifts
Every source of light has its own color. These color values range from the very warm tones at 1000K (candlelight) upward to the very cool tones at 10000K (shade).
Because the perception of color is the result of light reflecting off a surface or a subject and because every source of light has its own color, photographers have to be aware of how a light’s color value in K° will impact the recorded color values of a scene.
If 5500K represents daylight/white light and we have a light source that is measured at 2800K, it is going to be a much warmer color of light. In this case, white is no longer truly white, but will appear more orange or yellow. Our brains attempt to trick us and think that if a white sheet of paper is white, we should always interpret it as white under almost all lighting conditions. We are simply programmed to see the colors as we know them.
Cameras do not have a brain to trick them. They simply record the color values of the reflected light coming from the scene. When we look at a photograph of a white sheet of paper that has been photographed under a 2800K light source and the camera’s white balance icon is set to the sun, the paper appears orange or yellow.
For that sheet of paper to appear white in the photograph, the photographer would have to recognize that the light source was 2800K and move the white balance setting from the sun to the light bulb icon which represents warm tungsten light. A camera that offers a Kelvin option could be set to the “K” setting and then dialed to 2800 in the camera’s white balance menu.
Photographers must deal with color shifts from all artificial light sources and from changes of the sun’s position. Color temperatures may range from 1,000 to 10,000.
A camera that offers the Kelvin option for white balance usually covers from 2200K to 10000K in 100° increments. If you add all those up, the Kelvin options provide the photographer with 79 distinctive white balance options.
The white balance icons represent only one of these 79 values for each icon. Since there are only 6 icons that represent a single setting, the camera can only get in the ballpark using these icons. The K setting clearly offers the opportunity for much more accuracy.
Accurate Color
There are plenty of reasons to record accurate color of any given scene or subject. Accurate color is often a priority for commercial photography. It could also be a priority for a bride who is wearing an off-white dress and desires her images to reflect this subtle hint of warmth to her dress.
There are times, however, when the photographer may wish to impose deliberate shifts to accurate color. A photographer may prefer slightly warmer skin tones for example. Perhaps a photographer would prefer slightly cooler/bluer tones in a snow scene to represent that it is cold or overly warm/red tones of a summer scene to emphasize the heat. These deliberate shifts in color are part of a photographer’s prerogative when it comes to capturing images.
Properties of Light
Properties of light include a look into some of the physics of light.
Angle of Incidence
If you throw a rubber ball straight into a wall, you can predict that the ball is going to come right back at you. If you throw that same ball into the wall at a 45° angle, it will bounce off the wall in the opposite direction and at the exact angle you threw it. The angle of incidence equals the angle of reflectance. Light travels in the same course that the ball does.
If you photograph a mirror straight on with a flash on the camera, you are going to see the resulting burst of flash in that mirror because the light bounces straight back to you just like the ball. However, if you take a few steps to the side and photograph that same mirror with the same flash, the reflection of the flash comes off the mirror at the opposite direction and at the same angle.
This principle recognizes the path that light travels relative to a normal path. For photographers, normal is the line created between the camera position and the subject. If you are behind the camera, facing your subject, and the main light is exactly behind you, the angle of incidence is 0°. Move the light so that it is at 45°, the angle of incidence is now 45° and the angle of reflectance is also 45°.
Light bounced off of a highly reflective surface returns the light more efficiently than dull or matte surfaces. Glossy surfaces reflect more light than rough surfaces.
Lighting that is reflected or bounced off of a surface will also take on the color of that surface.
Size of the Light
The size of the light source relative to the subject determines its relative hardness or softness. It also impacts the size and intensity of highlights and the hardness or softness of the shadows.
Smaller light sources tend to create specular highlights and harder transitions between highlight and shadow.
Larger light sources tend to create diffused highlights and softer transitions between highlight and shadow.
The small portable flash created strong specular highlights on her forehead and down the bridge of her nose and a small highlight at the tip of her nose (left).
The transition of the highlight and shadow on her nose and cheek is very abrupt.