Vision, Color and Vision, Color and Electromagnetic Electromagnetic

WavesWavesChapter 22.1 and 22.2, 24Chapter 22.1 and 22.2, 24

Light can reach your eyes in Light can reach your eyes in one of two ways:one of two ways:

1.Light1.Light can come directly can come directly from an object that from an object that produces produces its own light, such its own light, such as a light bulb.as a light bulb.

2.Light2.Light can be reflected can be reflected from objects that from objects that do not do not produce produce their own light, their own light, such as clothes.such as clothes.

ColorColor is how we perceive the is how we perceive the energy of lightenergy of light..

White lightWhite light is a combination of is a combination of all of the colors of light or the all of the colors of light or the rainbow. rainbow. Ex.Ex. Sun and electric Sun and electric lightslights

All of the colors in the rainbow All of the colors in the rainbow are light of different are light of different energies.energies.

- - RedRed has the has the lowestlowest energy. energy. - - VioletViolet has the has the highesthighest energy. energy.

Red,Orange,Yellow,Green,Blue,Violet

White light continuedWhite light continued Objects appear different colors Objects appear different colors

because they because they absorb absorb some colors some colors and and reflect reflect others.others.

ExEx. an . an orangeorange absorbs all colors of absorbs all colors of the light spectrum except the light spectrum except orangeorange (this it reflects) which is the color (this it reflects) which is the color you see.you see.

Pigments work by Pigments work by subtractingsubtracting colors colors from white light.from white light.

How We See ColorsHow We See Colors Additive (or RGB) Color Process - Additive (or RGB) Color Process - a a

process that creates color by adding process that creates color by adding proportions of proportions of red, green, and blue red, green, and blue together.together.

We perceive colors as We perceive colors as percentagespercentages of of 3 3 additive primary colorsadditive primary colors: red, green, : red, green, & blue.& blue.

Using ColorUsing Color

Subtractive (or CMYK ) Color Process- Subtractive (or CMYK ) Color Process- A process that creates color by A process that creates color by subtractingsubtracting colors from white light colors from white light using using absorption.absorption.

We perceive colors as a combination We perceive colors as a combination of percentages of 3 of percentages of 3 subtractive subtractive primary colorsprimary colors: cyan, magenta, : cyan, magenta, yellow.yellow.

CMYK Color ProcessCMYK Color Process CMYK processCMYK process is another name for is another name for

the the subtractivesubtractive color process. color process. It stands for It stands for cyan, magenta, yellowcyan, magenta, yellow, ,

and black.and black. The CMYK color process is used for The CMYK color process is used for

making all colors seen in making all colors seen in reflectedreflected light, including printing inks and light, including printing inks and fabric dyes. Cyan, magenta, and fabric dyes. Cyan, magenta, and yellow are yellow are combined combined in various in various proportions to make any color.proportions to make any color.

The Human EyeThe Human Eye Light enters your eye through the Light enters your eye through the lenslens and and

lands on the lands on the retinaretina (a membrane in back (a membrane in back eye) eye)

On the surface of the retina are On the surface of the retina are light-light-sensitivesensitive cellscells called called photoreceptorsphotoreceptors..

When light hits a When light hits a photoreceptorphotoreceptor, the cell , the cell releases a chemical signal that travels releases a chemical signal that travels along the along the optic nerve optic nerve to the to the brainbrain. .

The brain translates the signal into the The brain translates the signal into the perception of colorperception of color..

Some photoreceptors respond only to Some photoreceptors respond only to lowlow energy and others only to energy and others only to highhigh energy. energy.

Two Types of PhotoreceptorsTwo Types of Photoreceptors ConesCones respond respond to colorto color and there are 3 and there are 3

types:types: 1) responds to 1) responds to red lightred light (lowest energy) (lowest energy) 2)responds to 2)responds to green lightgreen light 3) responds to 3) responds to blue lightblue light (highest energy) (highest energy)

We see white light when all 3 cones are We see white light when all 3 cones are equallyequally stimulated. stimulated.

RodsRods respond only to difference in respond only to difference in intensityintensity..

Rod cells detect Rod cells detect blackblack, white, , white, and and graygray..

Electromagnetic Spectrum The light that we can see with our eyes

is just a small part of the full spectrum of light that occurs in nature. We call this the electromagnetic spectrum.

Because light is a composite of interacting electric and magnetic force fields. The spectrum extends from low energy microwaves and infrared light to the visible light, and then to more energetic forms of light such as ultraviolet and x-rays.

Electromagnetic WavesElectromagnetic Waves Wavelengths Wavelengths of light come in a of light come in a

range of range of sizessizes. . Electromagnetic waves have Electromagnetic waves have both both

magnetic magnetic andand electrical electrical qualitiesqualities. . They exchange They exchange energyenergy back and back and

forth. Each forth. Each cyclecycle of the of the electricelectric part of the wave creates a part of the wave creates a magnetic wave as it changes and magnetic wave as it changes and vice versa.vice versa.

Properties of Electromagnetic waves

Frequency Wavelength Amplitude Speed -same in a vacuum (3x108 m/sec) Carry energy in proportion to their

frequency. Higher frequency=Higher energy High frequency of light (color)=High energy

Invisible, with the exception of visible light As Frequency increases, wavelength

decreases

Radio wave, an electromagnetic wave.

If you switch electricity on and off in a wire, the oscillating electricity makes an electromagnetic wave.

Oscillating electric current in a radio tower makes ripples of electricity and magnetism that spread out from the radio tower at the speed of light as electromagnetic waves (radio waves).

Lowest frequency wave Used in wireless networking, TV,

Radio and Radar

Microwaves and Infrared Waves

Length- 30cm (12 in.) to 1mm

Cell phones use these

Microwave oven tune microwaves to the natural frequency of water. Microwaves transfer energy to water molecules in the food to heat food.

Length- 1mm to 700 nano’s

Infrared waves called radiant heat.

Heat from the sun.

Used in heat lamps and TV remote controls.

The Sun in three colors of UV light. Only active regions emit energetic UV light, so the colorful portions show the Sun’s hottest and most violent areas.

The solar emission of visible light has been stable over the past five billion years.

X rays and Gamma Rays High frequency

wave Length- 10nm to

0.001 nm Used in medical and

manufacturing X rays are absorbed

by your bones to make an X ray film

Dangerous to body if exposed long time

Highest frequency Smallest

wavelength Generated in

nuclear reactions Highest energy Dangerous to

body Used in medicine

and research

Temperature and Light It turns out that all objects with a

temperature above absolute zero radiate light.

The amount and kind of light that is radiated depends upon the object's temperature.

The higher the temperature, the more light is radiated, and the more energetic the light.

That's why blacksmiths heating up a horseshoe first see it begin to glow red, and then white as it gets hotter.

Temperature and Light continued

The Sun's surface, which has an avg. temperature of 10,000 degrees Fahrenheit (5810 degrees Kelvin), primarily radiates visible light. That's why we can see sunlight.

The surface of the Earth has an avg. temperature of 60 degrees Fahrenheit (288 degrees Kelvin), so it radiates in the infrared part of the spectrum. We can't see the light the Earth radiates.

Greenhouse Gases: water (H2O), carbon dioxide (CO2), methane (CH4), and nitrous

oxide (N2O). The temperature of an object is determined by a

balance between incoming and outgoing energy. For the Earth, the incoming energy is the

absorbed light from the Sun, and the outgoing energy is the infrared light the Earth radiates out to space.

“Greenhouse gases" have a very special property. They do not absorb the visible light from the sun, but they do absorb the infrared light radiated by the Earth's surface.

Without an atmosphere with its Greenhouse Effect, that balance would lead to very cold temperatures - well below the freezing point of water.

This process is known as the Greenhouse Effect.

If greenhouse gases were not in the atmosphere, all the infrared light radiated by the Earth would go back out to space, leaving the Earth too cold for life.

But the greenhouse gas molecules absorb the infrared light, and then re-radiate some of it back to the Earth's surface.

This makes the surface hotter so it radiates more light, thus establishing an equilibrium at a higher temperature.