Light and How We See

Reprinted from Skip Henne Photography
HOW WE SEE:
The human eye looks basically like the crude drawing to the right. The lens at the left side of the eye focuses light rays onto the retina at the right. The retina converts light rays into "electrical impuses" that are sent to the brain and our brain tells us we are seeing a bit of light.
eye.gif
camera_slr.gif
A camera (digital or film) has a lens out front to capture light rays, but those rays land on film or a digital chip.... both of which are sensitive to light. Now we are jumping ahead of ourselves, let's get back to basics.

ABOUT LIGHT RAYS:
We have different labels for describing the rays we see. Here are a few basic ones:
Transmitted rays: When you look at a stop light the top light is red, the middle is yellow and the bottom light is green. That light is transmitted by putting a light source behind a colored filter.
Direct rays: When you look directly into the sun, or a camera's flash unit, or a flashlight ... that is direct light. The light you see is coming directly from the source.
Reflected rays: When you look at anything, you can see that object because direct light is shining on it and being reflected back into your eyes.
Ambient light: Think of ambient light as stray light - light rays that are being bounced around from all sorts of sources. If direct or reflected light on the subject is stronger your subject will appear clearer and less hazy.
Available light simply means whatever light is present ... not using a flash or other sources of light.

NOW ... ABOUT COLOR:
The COLOR of the subject is determined by the color of the light source and the color of the subject.
Photographic film records light as it actually is. Your eye/brain however, will always correct light back to "normal". Your brain compensates constantly.
That is.... if you are inside a place that is lit with light bulbs, those light bulbs actually transmit a reddish-brown light and white objects will be recorded on film as reddish-brown. However your brain will correct that light and a white object will appear white.
Same thing inside a place illuminated with flourescent bulbs. Flourescent bulbs actually transmit an ugly greenish-yellow light, but your brain corrects that light and it appears white to your eye. Film records that light as greenish-yellow.
flourescent.jpg
flourescentmag.jpg
Flourescent light contains green and yellow light only so photos turn out a bit "off" in color....
.... however, by using a magenta filter in front of the lens, the overall lighting is more natural and "warm".
Photographers must use filters to correct those light sources back to "daylight" quality.
We will discuss this at length later on. Right now just understand that it happens.
RED light rays only contain red because it is a primary color. So GREEN light rays only contain green, and BLUE rays only contain blue. Again, that is because these are the PRIMARY colors.
Secondary colors - magenta, cyan, and yellow are considered SECONDARY colors because each one is a mix of two PRIMARY colors. Mixing PRIMARY & SECONDARY colors will give you TERTIARY (third tier) colors .... making up all the visible colors in the spectrum.
You can see how PRIMARY colors and SECONDARY colors mix from the chart below:
spectruma.jpg
Do Not Worry..... there will be no test on that. Just read it and think about it for a while.