Light and the Human Eye

Lesson (2)

Photography Class #2

The human eye looks basically like the crude drawing below. 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 impulses that are sent to the brain.  Our brain then tells us we are seeing a bit of light.

Eye Light

Light and Camera

Both digital and film cameras have a lens in front to capture light rays. Light rays enter through the lens to the film, or digital sensor; both of which are sensitive to light.  Instead of jumping ahead of ourselves, let’s get back to the 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, a camera’s flash unit, or a flashlight you are looking at 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

Available light simply means whatever light is present when not using a flash or other sources of light.

Understanding 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 is constantly compensating.

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 happens inside a place illuminated with fluorescent bulbs. Fluorescent 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.

Fluorescent light contains only enough green and yellow light to 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”.

We will discuss this at length later on. Right now just understand that it happens.

RED GREEN and BLUE are Primary Colors

Some people (see some of the comments below) just refuse to believe that green could be a primary color! Well if you’re still not a believer check out how red and green make yellow.

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:


Here’s another image to show you how using the primary colors, red, green and blue, you can produce the secondary colors.

rgb illumination

Do Not Worry, there will be no test on this. Just read it and think about it for a while. This concept can be a little confusing as in school we learned that the primary colors are different. We must remember that color in the printing world is what we learned in school, but color combinations are different for light. For photography, we must learn the colors of light, not the colors for printing. In photography we are talking about RGB or colors of light that join together to make white, whereas in print all primary colors joined together would create a neutral color, or gray.

Right now let’s go on to Photography Lesson #3: Lenses


110 thoughts on “Light and the Human Eye

  1. JD Willemsen

    Might be an idea to share.

    The pixels of a color tv is a great example for additive colors.

    Great site!, seems i didn’t missed much from my youth, where my dad was an analogue photographer


    From Holland

  2. jhen caloz

    this is great! i’m a beginner in photography and i was thinking of paying an online course for $200/month for six months but this one teaches me a lot and is very easy to understand.. at first i was a little confused but with the pictures and everything it makes me easy to understand.. not much of confusing terms and if there is they define it to a layman’s term. great website..

  3. Nicole Ramos

    This lesson really did help me out. I really got me to understand the out the primary colors and the lighting. I have to be truthful but when I did talk some classes on the at a JR. College. They were not so clear about Lighting and light blubs and the effect with color. I now can keep this in mind when it comes to taking my photos in a room with lights and also understanding the primary and secondary colors.

  4. Tania Sharma

    Great lesson… I have to make a note of this important points or else I will really forgot… 😀 next lesson please…

  5. Janis Dean

    Thank you! I am almost 60 years old and I learned something today because of this lesson on primary light colors. They say you keep your brain young by learning at least one thing new each day.

  6. Kay

    Wow. My eyes lie to me! I knew I loved my camera, but I was unaware I could trust it more than my own two eyes! This site is really helping me out! I have been interested in photography my whole life, but recently have flirted with the idea of making it a career. I am finding this site very helpful in helping me make my way in that direction. I am continuing on and am hoping to learn more!

  7. Henry

    Mind blown on the Primary Colors. But now I know why I suck at color correction in Photoshop.

  8. nick

    blue,red,yellow primary colors in paint .. blue,red,green primary colors in light .. that course we learn t on school. :)

  9. michelle

    Thank you so much. These lessons are exactly what I was looking for to start learning how to be a good photographer. I really appreciate it, and that it is free, most of all!

Leave a Reply

Your email address will not be published. Required fields are marked *