Two equally true statements:

• The only thing we can hear is sound.

• The only thing we can see is light.

How do we see color?

The color of an object is not actually within the object itself. Rather, the color is in the light that shines upon it and is ultimately reflected to our eyes.

How do we see color?• When visible light strikes an object and a specific frequency becomesabsorbed, that frequency of light will never make it to our eyes.

• Any visible light that strikes the object and becomes reflected to our eyes will contribute to the color appearance of that object. So the color is not in the object itself, but in the light that strikes the object and ultimately reaches our eye.

How do we see color?

The only role that the object plays is that it might contain atoms capable of selectively absorbing one or more frequencies of the visible light that shine upon it. So (for example), if an object absorbs all of the frequencies of visible light except for the frequency associated with green light, then the object will appear green.

Check your understanding:

White light shines on both papers. What color will each paper appear to be?

Transparent Objects

Transparent materials allow one or more of the frequencies of visible light to be transmitted through them; whatever colors are not transmitted are typically absorbed by them. The appearance of a transparent object is dependent upon what colors of light are incident upon the object and what colors of light are transmitted through the object.

Check your understanding

Two pieces of colored, transparent glass are shown below. What color are they?

Primary Colors• When we speak of white light, we are referring to

ROYGBIV - the presence of the entire spectrum of visible light. But combining all the frequencies in the visible light spectrum is not the only means of producing white light.

• White light can also be produced by combining only three distinct frequencies of light, provided that they are widely separated on the visible light spectrum.

• The three colors of light that produce white light when combined with the correct intensity are called primary colors of light.

• The most common set of primary colors is red, green, and blue.

Rods and Cones in the Retina:Remember, the cones are red,

green, and blue.

Light is perceived as white by humans when Light is perceived as white by humans when all three cone cell types of the eye are all three cone cell types of the eye are simultaneously stimulated by equal amounts simultaneously stimulated by equal amounts of red, green, and blue light. Because the of red, green, and blue light. Because the addition of these three colors yields white addition of these three colors yields white light, the colors red, green, and blue are light, the colors red, green, and blue are termed the primary additive colors.termed the primary additive colors.

Click on this hyperlinked address to access a terrific interactive website doing the above or use a set of flashlights.http://micro.magnet.fsu.edu/primer/java/primarycolors/additiveprimaries/index.html

The three outer colors are the colors of light which pair up to form the interior shades shown. The outside 3 The outside 3 together to make together to make the “white in the the “white in the middle”middle”

The secondary colors of light are yellow, magenta, and cyan.

red + blue = ________ red + green = _______ blue + green = _______

Check your understanding

Two lights are arranged above a white sheet of paper. Determining the color that the sheet of paper will appear in the diagrams below.

Complementary Colors

• Any two colors of light that when mixed together in equal intensities produce white are said to be complementary colors of each other.

Complementary Colors

The complementary color of red light is cyan light. This is reasonable since cyan light is the combination of blue and green light; and blue and green light when added to red light will produce white light. Thus, red light and cyan light (blue + green) represent a pair of complementary colors; they add together to produce white light.

Color Subtraction

• Consider a shirt made of a material that is capable of absorbing blue light. Such a material will absorb blue light (if blue light shines upon it) and reflect the other frequencies of the visible spectrum. What appearance will such a shirt have if illuminated with white light and how can we account for its appearance?

Color Subtraction

Consider white light to consist of the three primary colors of light - red, green and blue. If white light is shining on a shirt, then red, green and blue light is shining on the shirt. If the shirt absorbs blue light, then only red and green light will be reflected from the shirt. Red and green light striking your eye always gives the appearance of yellow; for this reason, the shirt will appear yellow.

When you stare at the coming pictures, your eyes will do color subtraction……… you exhaust the ability to see some colors, all that’s left are the other colors….. Color Subtraction !

• The human eye has cone cells for detecting red, blue, and green light. These cells are used for daylight vision.

• Rod cells are used in night vision since they detect only light and dark.

Stare at the center of the circle in the next slide.

CyanCyan is composed of blue and green. After staring at cyan for a long time, you have exhausted the blue and green cone cells in your eye.

Therefore, when you look at white, you see redred after staring at cyancyan.

When have you ever experienced this phenomenon?

When someone takes your picture using a flashbulb, you see black spots. The flashbulb

exhausted all of the cone cells in your eye so none of them were

working for a few moments, and you don’t see any light.

Stare at the center of the circle in the next slide.

YellowYellow is composed of red and green. After staring at yellowyellow for a long time, you have exhausted the red and green cone cells in your eyes.

Therefore, you see blue after staring at yellowyellow.

Stare at the center of the circle in the next slide.

Magenta is composed of red and blue. After staring at magenta for a long time, you have exhausted the red and blue cone cells.

Therefore, you see green after staring at magenta.

Your eyes are capable of more complicated shapes than circles. Stare at the center of the heart on

the next slide.

You should have seen a red heart after staring at the cyancyan heart since you have exhausted the green and blue cone cells from staring at cyancyan.

Stare at the center of the next slide.

You should have seen a green smiley face since your blue and red cone cells were exhausted from staring at the magenta smiley face.

Your eyes are capable of resolving an even more

complicated picture. Stare at the center of the next slide.

Your eyes are capable of resolving an even more

complicated picture. Stare at the center of the next slide.

The U.S. flag was originally cyancyan, yellowyellow and black.

After it was removed it appeared red, whitewhite, and blue.

If NONO color reaches your eyes, you see BLACK.

If ALLALL color reflects and reaches your eyes you see WHITEWHITE .

Stare at the center of the even more

complicated picture.

Test yourself for colorblindness!

• Color blindness usually involves the colors of red and green.

• Color blindness is found in 4% of the male population and 0.25% of the female population.

• Color blindness is a sex linked recessive genetic trait that appears on the X chromosome.

• Since men have only one X chromosome, if the gene for color blindness appears on it, they will be color blind.

• Women have two X chromosomes and it would have to appear on both X chromosomes before the woman would exhibit the trait.

What do you see in the next slide?

• Everyone should have seen the number 25.

What do you see in the next slide?

• If you have normal vision you should see the number 29.

• If you are red-green color blind you will probably only see spots.

What do you see in the next slide?

• If you have normal vision you should see the number 45.

• If you are red-green color blind you will probably only see spots.

What do you see in the next slide?

•Everyone should see the number 56.

What do you see in the next slide?

• If you have normal vision you should see the number 6.

• If you are red - green color blind you will probably only see spots.

What do you see in the next slide?

• If you have normal vision you should see the number 8.

• If you are red - green color blind you will probably only see spots.

What NUMBER do you see in the next slide?

• The individual with normal color vision will see a 5 revealed in the dot pattern.

• An individual with red - green (the most common) color blindness will see a 2 revealed in the dots.