Light Can Act Like Waves Light Can Act Like Waves or Particlesor Particles

In 1801 Thomas Young an English In 1801 Thomas Young an English scientist did the Double slit experiment.scientist did the Double slit experiment.

Passed a beam of light through two narrow Passed a beam of light through two narrow openings and projected it onto a screen.openings and projected it onto a screen.

He found the light produced a striped pattern He found the light produced a striped pattern which meant the light was constructively and which meant the light was constructively and destructively interfering.destructively interfering.

This meant that light is composed of waves.This meant that light is composed of waves.

But Light can Also But Light can Also Behave like a ParticleBehave like a Particle Other observations indicated that light Other observations indicated that light

can also act like a particle:can also act like a particle:– When light hits metal it knocks electrons off When light hits metal it knocks electrons off

the surface.the surface.– They found that red light cannot knock They found that red light cannot knock

electrons off metal no matter how bright it is.electrons off metal no matter how bright it is.– If light were a wave then the brighter light If light were a wave then the brighter light

should have more energy.should have more energy.– PhotonsPhotons are light particles that contain are light particles that contain

certain amounts of energy based on their certain amounts of energy based on their frequency and wavelength.frequency and wavelength.

– Blue light has a higher frequency and shorter Blue light has a higher frequency and shorter wavelength thus contains more energy than red wavelength thus contains more energy than red light.light.

Relationship Between Frequency, Wavelength and Energy

The Color of light is Determined The Color of light is Determined By its Frequency and By its Frequency and WavelengthWavelength

Red Red 650 - 720 nm650 - 720 nm Orange Orange 570 - 650 nm570 - 650 nm YellowYellow 530 - 570 nm530 - 570 nm Green Green 480 - 530 nm480 - 530 nm BlueBlue 440 - 480 nm440 - 480 nm IndigoIndigo 410 - 440 nm410 - 440 nm VioletViolet 380 – 410 nm380 – 410 nm

The Perception of The Perception of ColorColor

Our perception of blending colors is created by how Our perception of blending colors is created by how our eyes function.our eyes function.– If a beam of If a beam of redred light and a beam of light and a beam of yellow yellow light are light are

shined together we do NOT perceive shined together we do NOT perceive orange orange light.light.– Your eyes contain receptors called Your eyes contain receptors called conescones that are that are

sensitive to sensitive to redred , , greengreen , and , and blueblue light. light.– These are known as the primary colors.These are known as the primary colors.

If only the blue cones are stimulated then we will only If only the blue cones are stimulated then we will only perceive blue light.perceive blue light.– If more than one type of cone is stimulated then we will If more than one type of cone is stimulated then we will

perceive a new color.perceive a new color.– These are known as These are known as secondary colorssecondary colors..– If all three types of cones are stimulated we perceive If all three types of cones are stimulated we perceive

white.white.– If none of the cones are stimulated we don’t see any If none of the cones are stimulated we don’t see any

color or perceive black.color or perceive black.

The frequency and wavelength of light The frequency and wavelength of light determine what color you will see.determine what color you will see.– When you optical receptors perceive a When you optical receptors perceive a

wavelength of 550 nm you see green light.wavelength of 550 nm you see green light.– The colors that you see are a result of surfaces The colors that you see are a result of surfaces

reflecting various wavelengths of light back to reflecting various wavelengths of light back to your eyes.your eyes.

– White lightWhite light When all of the primary colors are being reflected When all of the primary colors are being reflected

back to your eyes.back to your eyes.

– No light (or black)No light (or black) When all of the primary colors are being absorbed When all of the primary colors are being absorbed

and no light is being reflected back to your eyes.and no light is being reflected back to your eyes.

The Brightness of Light The Brightness of Light Depends on IntensityDepends on Intensity

IntensityIntensity– The quantity of light illuminating a The quantity of light illuminating a

surfacesurface..– Depends on the amount of light passing Depends on the amount of light passing

through a certain area or space.through a certain area or space.– Light spreads out in spherical wave Light spreads out in spherical wave

fronts.fronts.– Light is more diffuse further from its Light is more diffuse further from its

source.source.

Primary PigmentsPrimary Pigments

Pigments are substances that absorb Pigments are substances that absorb light.light.

The primary pigments are:The primary pigments are:– Cyan Cyan Magenta Magenta YellowYellow

These are also known as the These are also known as the subtractive colorssubtractive colors..– Adding any of these two colors together Adding any of these two colors together

give you back the primary colors.give you back the primary colors.

ROYGBIV

Human Eye Cone Sensitivities

Color Addition

• Reflected Red + Green = Yellow

• Reflected Blue + Green = Cyan

• Reflected Blue + Red = Magenta

Color AdditionColor Addition