Light and Color

If you went into a room and completely blocked out any outside light and you turned out the light in the room, would you be able to see anything in the room?

The Nature of Light Everything we see is light reflected off other objects. If you were to be in a completely closed room with no light source, you’d never be able to see anything. (Your eyes would never adjust). Light reflects off objects and enters our eyes. This is how we see things.

The Nature of Light What is light? Scientists debated whether light was a wave or a particle. Turns out, light is both a particle and a wave. This is known as wave-particle duality. Light can exhibit properties of both waves and particles depending on what way we are studying it.

The Nature of Light Particles of light are called photons.

The Nature of Light Light is an electromagnetic wave that can move through the vacuum of space.

The Nature of Light The speed of light is the fastest speed in the universe. Nothing can travel faster or even as fast as the speed of light. All light travels at 3 x 10 8 m/s in a vacuum. The speed of light is abbreviated “c”. The distance light travels in 1 year is called a light year.

Light years are used for distances in space because the distances are so great. The distance to the next nearest star, Alpha Centauri is 4 light years. This means that we are seeing this star as it looked 4 years ago when the light left the surface of the star. If we put this distance into miles or km, the distance is 23,650,000,000,000 miles or 37,840,000,000,000 km. And this is for the closest star (after the sun)!

The Nature of Light When light moves through any medium (i.e. water, glass, air) it slows down. The amount that light slows down when moving in air is so small that we can say the speed of light in air is still 3 x 10 8 m/s.

A transparent material allows all light through. What are the two transparent materials in the photos below?

Translucent materials let light through but the light gets diffused so that you can’t see objects clearly.

Opaque materials do not allow light to pass through.

The Electromagnetic Spectrum The light we see only accounts for a small portion of all light. The electromagnetic spectrum includes radio waves, microwaves, infrared light, visible light, UV light, x-rays, and gamma rays.

Visible Light White light is a combination of all colors of light.

Visible Light Although all colors of light combined will yield white light, not all colors are necessary. The three primary colors of light are RED GREEN BLUE. The three primary light colors combined will give white light. Note that these are different from the primary pigment colors you learned in art class.

Color Addition Mixing the primary colors gives the secondary colors of light.

Color Addition RED + BLUE = MAGENTA GREEN + BLUE = CYAN RED + GREEN = YELLOW

FOR FUN

Complimentary Colors Complimentary Colors are those that when added together produce white light. The complimentary colors are: red + cyan = white blue + yellow = white green + magenta = white

Color When light shines on an object, some light is reflected, some light is absorbed. The color of the object is a result of the light that is reflected. If you are wearing a red shirt, your shirt is absorbing all colors but red. What colors are absorbed if your shirt is white? What colors are absorbed if your shirt is black?

Check for Understanding

Color Subtraction Let’s answer the question: What happens when a yellow light shines on a cyan shirt? A cyan shirt will absorb red and reflect green and blue. The yellow light is made of red and green. The shirt will absorb the red and reflect the green so it will look green.

Check for understanding What color will a blue object look when illuminated with a magenta light? The object will absorb green and red. Magenta is red and blue. The object will absorb the red and reflect the blue. The object will look blue. What if the light is yellow? Yellow is red and green. The object will absorb the red and green making it appear black.

Interesting Stuff: Color Blindness Causes, incidence, and risk factors Color blindness occurs when there is a problem with the color-sensing materials (pigments) in certain nerve cells of the eye. These cells are called cones. They are found in the retina, the light-sensitive layer of tissue at the back of the inner eye. If you are missing just one pigment, you might have trouble telling the difference between red and green. This is the most common type of color blindness. Other times, people have trouble seeing blue-yellow colors. People with blue-yellow color blindness almost always have problems identify reds and greens, too.

Color Blindness The most severe form of color blindness is achromatopsia. A person with this rare condition cannot see any color. Achromatopsia is often associated with lazy eye, nystagmus (small, jerky eye movements), severe light sensitivity, and extremely poor vision. Most color blindness is due to a genetic problem. About 1 in 10 men have some form of color blindness. Very few women are color blind.

Are You Colorblind? VISUAL ACUITY: A person who has sufficient visual acuity should see the number twelve in the circle on the left whether or not they have normal color vision. COLOR BLINDNESS: A person with normal color vision sees a number seven in the circle on the left. Those who are color blind usually do not see any number at all.

Are You Colorblind? RED-GREEN COLORBLINDNESS: People with red-green color blindness see either a three or nothing at all. Those with normal color vision see an 8. PROTANOPIA & DEUTERANOPIA Those with normal vision see the number thirty-five in the circle above. A person with protanopia sees only he number five. A person with deuteranopia sees the number three. People who are partially color blind will see both numbers but one more distinctly than the other.

Polarization Light waves travel from an object in all directions but for simplicity, we will say that light only travels out in the vertical and horizontal direction.

Polarization When light is polarized, only part of the waves get through. If two polarizing filters are held perpendicular to one another, no light will get through

Spectrum The amount of light we can see is a very small portion of all light. All light (what we can and cannot see) makes up the electromagnetic spectrum. Electromagnetic waves is a fancy way of saying light waves.

The Spectrum

Electromagnetic waves are transverse waves. Electromagnetic waves do not need a medium, they can travel through the vacuum of space.

Radio Waves Radio waves are light waves. Radio waves have the longest wavelength of all light waves. Radio waves have a big range of wavelengths, some are bigger than a football field, some are the size of a loaf of bread. Radio waves can move through your body.

Extra Information (don’t need to write this down) Astronomers use radio telescopes to get information from distant galaxies. Since radio waves have such looooong wavelengths they can travel through space without much messing them up (like gasses and dust that they travel through). The following two pictures are radio telescopes. They don’t look like a typical telescope but they gather light from a star or galaxy just like a regular telescope with a mirror does.

VLA (Very Large Array)

Aercibo

Microwave Microwaves are about the size of a bee. Used to cook foods, track weather, radar

Infrared Infrared light waves are about the size of the head of a pin. Every object gives off infrared light.

Visible Light The light we see is called visible light. ROYGBIV Red, longest wavelength, least energy Violet, short wavelength, tons of energy

Ultraviolet Ultraviolet (UV) light waves are about the size of a molecule. Causes sunburns, cancer, wrinkles Gives our body Vitamin D

X ray X-rays have very small wavelengths Used to see bones, teeth

One of the first ever x-rays

Gamma Rays Gamma rays are the highest energy light waves. Super tiny wavelength