Visible Light and Its Sources. The Visible Spectrum Light is visible at wavelengths of about 780 nm to 380 nm. We see light as colors, not as waves. Light

Visible Light and Its Sources

Visible Light and Its Sources

The Visible SpectrumThe Visible Spectrum• Light is visible at wavelengths

of about 780 nm to 380 nm. • We see light as colors, not as

waves.

• Light is visible at wavelengths of about 780 nm to 380 nm.

• We see light as colors, not as waves.

gammagammax-rayx-ray

UVUV

IRIR

ELFELF

UHFRADARTV FMVHFAM

UHFRADARTV FMVHFAM

VLFVLF

101101

10101010

10201020

Fre

qu

ency

(H

z)F

req

uen

cy (

Hz)

700700 650650 600600 550550 500500 450450 400400

400400 450450 500500 550550 600600 650650 700700 750750

Frequency (THz)Frequency (THz)

Wavelength (nm)Wavelength (nm)

The Visible SpectrumThe Visible Spectrum• Luminous objects produce light.

Ideally – emits a continuous spectrum (all possible wavelengths of visible light)• The sun comes close to

emitting a continuous spectrum, but it does have some gaps.

• Luminous objects produce light. Ideally – emits a continuous

spectrum (all possible wavelengths of visible light)• The sun comes close to

emitting a continuous spectrum, but it does have some gaps.

The Visible SpectrumThe Visible Spectrum• Luminous objects produce light.

Monochromatic – emits a single color (a single wavelength of visible light)

Other light sources – emit multiple distinct colors

• Luminous objects produce light. Monochromatic – emits a

single color (a single wavelength of visible light)

Other light sources – emit multiple distinct colors

The Visible SpectrumThe Visible Spectrum• Light projected through a prism

produces a line spectrum. line spectrum – distinctly

visible lines of color can be seen at specific wavelengths aligned along a scale in a spectrograph

• Light projected through a prism produces a line spectrum. line spectrum – distinctly

visible lines of color can be seen at specific wavelengths aligned along a scale in a spectrograph

The Visible SpectrumThe Visible Spectrum spectroscope – an

instrument designed to display the line spectrum

spectrograph – a photo of the spectrum

spectroscope – an instrument designed to display the line spectrum

spectrograph – a photo of the spectrum

QuestionQuestion

Which of the following is a luminous object?Which of the following is a luminous object?

1. Light bulb2. T-shirt3. Piece of paper4. Window

1. Light bulb2. T-shirt3. Piece of paper4. Window

• depends on the material through which it travels

• defined as 299,792,458 m/s (can be rounded to 300 million m/s)

• depends on the material through which it travels

• defined as 299,792,458 m/s (can be rounded to 300 million m/s)

The Speed of LightThe Speed of Light

• If 300 million m/s is 18 million km/min, then sunlight takes…about 8.3 light-minutes to

reach Earth.…about 4.2 light-hours to

reach Neptune.

• If 300 million m/s is 18 million km/min, then sunlight takes…about 8.3 light-minutes to

reach Earth.…about 4.2 light-hours to

reach Neptune.


• If 300 million m/s is 18 million km/min, then sunlight takes…about 4.4 light-years to

reach the nearest star.…about 100,000 light-years to

travel the diameter of the Milky Way galaxy.

• If 300 million m/s is 18 million km/min, then sunlight takes…about 4.4 light-years to

reach the nearest star.…about 100,000 light-years to

travel the diameter of the Milky Way galaxy.


• The intensity, power, or brightness of a light source is the rate at which it radiates energy.

• Intensity is always measured at the source.

• The intensity, power, or brightness of a light source is the rate at which it radiates energy.

• Intensity is always measured at the source.

Intensity of LightIntensity of Light

• SI unit – candela (cd) It is just slightly brighter

than an average candle.


than an average candle.



than an average candle. An ordinary incandescent

bulb makes just less than 1 cd/watt.

Fluorescent lights emit about

4 cd/watt.


than an average candle. An ordinary incandescent

bulb makes just less than 1 cd/watt.

Fluorescent lights emit about

4 cd/watt.


QuestionQuestion

Approximately how many candles would be needed to give as much light as a 60 W light bulb?

Approximately how many candles would be needed to give as much light as a 60 W light bulb?

1. 102. 603. 954. 130

1. 102. 603. 954. 130

• Illumination is the amount of light received at a distance from the source.

• The amount of illumination depends on the brightness of the light source and the distance from it.

• Illumination is the amount of light received at a distance from the source.

• The amount of illumination depends on the brightness of the light source and the distance from it.


• Illumination and distance from the light source are related by the inverse-square law. Doubling the distance

reduces the illumination to one-fourth of the original illumination.

• Illumination and distance from the light source are related by the inverse-square law. Doubling the distance

reduces the illumination to one-fourth of the original illumination.


Tripling the distance reduces the illumination to one-ninth of the original.

Tripling the distance reduces the illumination to one-ninth of the original.


Distance and its effect on forces are often related by the

inverse-square law.

Distance and its effect on forces are often related by the

inverse-square law.

3 m3 m2 m2 m1 m1 m

1 m2 4 m2 9 m2 16 m2

4 m4 m

QuestionQuestion

If the distance is cut in half, the illumination will beIf the distance is cut in half, the illumination will be

1. quadrupled.2. doubled.3. cut in half.4. reduced to one-fourth.

1. quadrupled.2. doubled.3. cut in half.4. reduced to one-fourth.

• Photometers measure the illumination of light using a “solar cell.”

• More light equals more current.

• Photometers measure the illumination of light using a “solar cell.”

• More light equals more current.


1. Incandescent2. Fluorescent3. Phosphorescent

1. Incandescent2. Fluorescent3. Phosphorescent

Sources of LightSources of Light

• Incandescent bulbs have materials which are heated until they release visible energy.

• As the filament gets hotter, the light goes from red to yellow and on up the spectrum.

• Incandescent bulbs have materials which are heated until they release visible energy.

• As the filament gets hotter, the light goes from red to yellow and on up the spectrum.

IncandescentIncandescent

10001000

4000 K4000 K

3000 K3000 K

2000 K2000 K

00 20002000 30003000 40004000Wavelength (nm)Wavelength (nm)

Rel

ativ

e In

ten

sity

Rel

ativ

e In

ten

sity

• Fluorescent tubes contain mercury gas which emits light as the electricity passes through it.

• The light is in the UV range.• Phosphors absorb this light

and reemit it at a lower energy: the visible light range.

• Fluorescent tubes contain mercury gas which emits light as the electricity passes through it.

• The light is in the UV range.• Phosphors absorb this light

and reemit it at a lower energy: the visible light range.

FluorescentFluorescent

• A UV lamp is simply a regular fluorescent tube with little or no phosphors.

• A UV lamp is simply a regular fluorescent tube with little or no phosphors.

FluorescentFluorescent

low pressure argon and mercury gaslow pressure argon and mercury gas

glass tube

glass tube

phosphor coating

phosphor coating

mercurymercury

electrodeelectrode

• Phosphorescence occurs when the material continues to emit light when the source is removed.

• Phosphorescence occurs when the material continues to emit light when the source is removed.

PhosphorescencePhosphorescence

• Coherent light is “in step” or “in phase” and of the same color.

• Coherent light is “in step” or “in phase” and of the same color.

Coherent LightCoherent Light

• Lasers and certain LED (light-emitting diodes) produce coherent light.

• Since it is in phase, it does not spread out like ordinary visible light produced from a flashlight.

• Lasers and certain LED (light-emitting diodes) produce coherent light.

• Since it is in phase, it does not spread out like ordinary visible light produced from a flashlight.

Coherent LightCoherent Light

QuestionQuestion

T/F Laser light is monochromatic.

T/F Laser light is monochromatic.

TrueTrue

• Bioluminescence is light given off by living creatures like fireflies.

• It is produced from a chemical reaction inside the creature.

• Bioluminescence is also called cold light.

• Bioluminescence is light given off by living creatures like fireflies.

• It is produced from a chemical reaction inside the creature.

• Bioluminescence is also called cold light.

BioluminescenceBioluminescence

• Chemiluminescence is cold light produced non-biologically as in light sticks.

• Chemiluminescence is cold light produced non-biologically as in light sticks.

ChemiluminescenceChemiluminescence

The Nature of ColorThe Nature of Color

• Look at Image 15-14 on p. 361.• Is the ball red because you

perceive it as red or because it is red?

• This is a question of philosophy, not science.

• Look at Image 15-14 on p. 361.• Is the ball red because you

perceive it as red or because it is red?

• This is a question of philosophy, not science.

IntroductionIntroduction

Example:If a tree falls in the forest

and nobody hears it, did it make a sound?

Example:If a tree falls in the forest

and nobody hears it, did it make a sound?


• Scientifically, an object’s color depends on how your eyes perceive it.

• Scientifically, an object’s color depends on how your eyes perceive it.


Color MixingColor Mixing• There are two types of color

mixing.1. Additive (occurs in light)2. Subtractive (occurs in paint)

• There are two types of color mixing.1. Additive (occurs in light)2. Subtractive (occurs in paint)

Additive• Additive means that light is

being emitted.• The human eye distinguishes

three colors of light. These colors are called the additive primary colors or primary hues.

Additive• Additive means that light is

being emitted.• The human eye distinguishes

three colors of light. These colors are called the additive primary colors or primary hues.

Color MixingColor Mixing

Additive• The additive primary colors are

red, green, and blue.• When mixed they produce the

additive secondary colors: yellow, magenta, and cyan.

• If all three are mixed equally they produce white light.

Additive• The additive primary colors are

red, green, and blue.• When mixed they produce the

additive secondary colors: yellow, magenta, and cyan.

• If all three are mixed equally they produce white light.


Color MixingColor Mixing monochromatic lamps

• Color TVs, computer monitors, and cell phone screens take advantage of the eye and brain’s ability to mix colors.

• These screens display only red, green, and blue, yet the mixture of colors gives a multitude of shades of each color.

• Color TVs, computer monitors, and cell phone screens take advantage of the eye and brain’s ability to mix colors.

• These screens display only red, green, and blue, yet the mixture of colors gives a multitude of shades of each color.


Subtractive (Paints)• Subtractive means that the

colors are reflected.

Subtractive (Paints)• Subtractive means that the

colors are reflected.


white light green andsome yellow

reflected

other colors

absorbed

Subtractive (Paints)• Paints and pigments have three

subtractive primary colors: cyan, magenta, and yellow.

Subtractive (Paints)• Paints and pigments have three

subtractive primary colors: cyan, magenta, and yellow.


Subtractive (Paints)• Mixing two of the three

subtractive primary colors gives the subtractive secondary colors (which are also the additive primary colors): red, green, and blue.

Subtractive (Paints)• Mixing two of the three

subtractive primary colors gives the subtractive secondary colors (which are also the additive primary colors): red, green, and blue.


Subtractive (Paints)• For example, mixing magenta

and cyan paints gives blue paint.

Subtractive (Paints)• For example, mixing magenta

and cyan paints gives blue paint.


Subtractive (Paints)• Mixing all three subtractive

primary colors should give black.

• Because no pigment absorbs colors completely, mixing all three colors often results in some shade of brown.

Subtractive (Paints)• Mixing all three subtractive

primary colors should give black.

• Because no pigment absorbs colors completely, mixing all three colors often results in some shade of brown.


1. HSVHue Saturation Value

1. HSVHue Saturation Value

Color Perception SystemsColor Perception Systems

HH

S

VV

2. CMYKCyan Magenta YellowBlack

2. CMYKCyan Magenta YellowBlack

BB

RR GG

MM CC

YY

KK

Color Perception SystemsColor Perception Systems

QuestionQuestion

If red, green, and blue lights are mixed, what color will result?If red, green, and blue lights are mixed, what color will result?

1. black2. magenta3. yellow4. white

1. black2. magenta3. yellow4. white

QuestionQuestion

If red and blue lights are mixed, what color will result?If red and blue lights are mixed, what color will result?

1. cyan2. magenta3. yellow4. white

1. cyan2. magenta3. yellow4. white

Reflection & MirrorsReflection & Mirrors

Light RaysLight Rays• A light beam is made up of

many light waves traveling together in a straight line.

• These waves are represented by lines called rays.

• A light beam is made up of many light waves traveling together in a straight line.

• These waves are represented by lines called rays.

Types of ReflectionTypes of Reflection• Diffuse reflection is caused by

rough or uneven surfaces.• Diffuse reflection is caused by

rough or uneven surfaces.

• Specular reflection is caused by smooth surfaces.

• Specular reflection is caused by smooth surfaces.

Types of ReflectionTypes of Reflection

incident ray – the ray going to the surface

reflected ray – the ray bouncing off the surface

normal – a line perpendicular to the surface

incident ray – the ray going to the surface

reflected ray – the ray bouncing off the surface

normal – a line perpendicular to the surface

Reflection TermsReflection Terms

angle of incidence – the angle between the normal and the incident ray

angle of reflection – the angle between the normal and the reflected ray

angle of incidence – the angle between the normal and the incident ray

angle of reflection – the angle between the normal and the reflected ray


Law of Reflection – states that the angle of incidence equals the angle of reflectionThis law is true for all rays

and all types of surfaces.

Law of Reflection – states that the angle of incidence equals the angle of reflectionThis law is true for all rays

and all types of surfaces.


normal linenormal line

angle ofincidence

angle ofincidence

angle ofreflectionangle ofreflection

reflectedrayreflectedray

incidentray

incidentray

point of incidencepoint of incidence

QuestionQuestion

If the incident angle is 40°, what is the reflected angle?If the incident angle is 40°, what is the reflected angle?

1. 20°2. 40°3. 50°4. 140°

1. 20°2. 40°3. 50°4. 140°

Plane Mirror ReflectionPlane Mirror Reflection• A plane mirror is a flat mirror.• The reflected image appears to

exist an equal distance away on the opposite side of (behind) the mirror.

• No actual image exists at this location (behind the mirror), so it is called a virtual image.

• The image is reversed left to right.

• A plane mirror is a flat mirror.• The reflected image appears to

exist an equal distance away on the opposite side of (behind) the mirror.

• No actual image exists at this location (behind the mirror), so it is called a virtual image.

• The image is reversed left to right.

Curved Mirror ReflectionCurved Mirror Reflection

• A real image is formed from focused rays that could be projected onto a screen.

• A real image is formed from focused rays that could be projected onto a screen.

Concave MirrorsConcave Mirrors• Concave mirrors are mirrors that

“cave in” on the side exposed to light rays.

• The light rays must also obey the law of reflection.

• The light rays converge (meet) at one point called the principal focus or focal point.

• Concave mirrors are mirrors that “cave in” on the side exposed to light rays.

• The light rays must also obey the law of reflection.

• The light rays converge (meet) at one point called the principal focus or focal point.

principal optical axisprincipal optical axis

focal pointfocal point

center of

mirror

center of

mirror

Concave MirrorsConcave Mirrors• If the object is located further

from the mirror than the focal point, the image will be real and inverted.

• If the object is located further from the mirror than the focal point, the image will be real and inverted.

1122

33

1122

33

objectobject

imageimage

focal pointfocal point

Concave MirrorsConcave Mirrors• If the object is located at the

focal point, no image will result. • If the object is located at the

focal point, no image will result.

Concave MirrorsConcave Mirrors• If the object is located closer to

the mirror than the focal point, the image will be virtual and upright.

• If the object is located closer to the mirror than the focal point, the image will be virtual and upright.

Concave MirrorsConcave Mirrors

Convex MirrorsConvex Mirrors• Convex mirrors reflect light to

produce only virtual images of varying sizes, but the virtual images are always smaller than the original objects.

• Convex mirrors reflect light to produce only virtual images of varying sizes, but the virtual images are always smaller than the original objects.

All mirrors (plane, concave, or convex) produce images

by reflection only.

All mirrors (plane, concave, or convex) produce images

by reflection only.

Refraction&

Lenses

Refraction&

Lenses

• Refraction is the bending of light as it passes from one medium to another medium of a different optical density.

• Optical density is measured by comparing the speed of light in a vacuum to the speed of light in the material.

• Refraction is the bending of light as it passes from one medium to another medium of a different optical density.

• Optical density is measured by comparing the speed of light in a vacuum to the speed of light in the material.

Light RefractionLight Refraction

• If light enters a denser material, the light ray is refracted toward the normal line.



boundarysurface

boundarysurface

angle ofincidence

angle ofrefractionangle of

refractionangle ofincidence

angle ofrefractionangle of

refraction


• If light enters a less dense material, it bends away from the normal line.


• If light enters a less dense material, it bends away from the normal line.


angle of refractionangle of refraction

angle of incidenceangle of incidence

• As the angle of incidence of the light is increased, eventually the refraction will lie on the surface of the material.

• This angle is called the critical angle of incidence.

• As the angle of incidence of the light is increased, eventually the refraction will lie on the surface of the material.

• This angle is called the critical angle of incidence.


angle of refraction = 90°angle of refraction = 90°

critical angle of incidencecritical angle of incidence

• As the angle of incidence is increased further, no light is refracted.

• All the light is reflected back into the denser material.

• When this occurs it is called total internal reflection.

• As the angle of incidence is increased further, no light is refracted.

• All the light is reflected back into the denser material.

• When this occurs it is called total internal reflection.


totally internally reflected ray

totally internally reflected ray

angle of incidenceangle of incidence

angle of reflectionangle of reflection

• A fiber optic cable relies on the total internal reflection to transmit data and images.

• Endoscopes are tiny cameras which use fiber optic cables to transmit light rays.

• The use of endoscopes has reduced the risk and damage from exploratory surgery.

• A fiber optic cable relies on the total internal reflection to transmit data and images.

• Endoscopes are tiny cameras which use fiber optic cables to transmit light rays.

• The use of endoscopes has reduced the risk and damage from exploratory surgery.


• With mirrors, light reflects off a surface.

• With lenses, light refracts through the material.

• The refracted light either converges to a point or diverges (spreads out).

• With mirrors, light reflects off a surface.

• With lenses, light refracts through the material.

• The refracted light either converges to a point or diverges (spreads out).

LensesLenses

• Convex lenses are converging lenses.

• The light converges to the focal point which is on the opposite side of the lens from the object.

• Many of the terms from mirrors also apply to lenses.

• Convex lenses are converging lenses.

• The light converges to the focal point which is on the opposite side of the lens from the object.

• Many of the terms from mirrors also apply to lenses.

Convex LensesConvex Lenses

Convex LensesConvex Lensesprincipal optical axis

parallel rays lens

focal point

focal point

• Concave lenses are diverging lenses.

• Concave lenses are diverging lenses.

Concave LensesConcave Lenses

Concave LensesConcave Lenses

• If a person is nearsighted, the focal point is in front of the retina.

• Diverging lenses are used to correct this.

• If a person is nearsighted, the focal point is in front of the retina.

• Diverging lenses are used to correct this.

Eyesight CorrectionEyesight Correction

• If a person is farsighted, the focal point is behind the retina.

• Converging lenses are used to correct this.

• If a person is farsighted, the focal point is behind the retina.

• Converging lenses are used to correct this.

Eyesight CorrectionEyesight Correction

Normal VisionNormal Vision

FarsightedFarsighted

Farsighted CorrectedFarsighted Corrected

NearsightedNearsighted

Nearsighted CorrectedNearsighted Corrected

• The images produced by lenses are usually different sizes from the objects.

• If the image is larger than the object, the magnification factor is greater than 1.

• The images produced by lenses are usually different sizes from the objects.

• If the image is larger than the object, the magnification factor is greater than 1.

MagnificationMagnification

• If an instrument has several lenses, the magnification factors are multiplied together to get the total magnification.

• Telescopes and microscopes are examples of instruments where the magnification factors are combined.

• If an instrument has several lenses, the magnification factors are multiplied together to get the total magnification.

• Telescopes and microscopes are examples of instruments where the magnification factors are combined.


• Binoculars are basically a pair of telescopes.

– In this case, the magnification factor is the same for each side of the binocular.

• Cameras also use several lenses.

• Binoculars are basically a pair of telescopes.

– In this case, the magnification factor is the same for each side of the binocular.

• Cameras also use several lenses.


QuestionQuestion

T/F A lens that looks like this will focus light.

T/F A lens that looks like this will focus light.

TrueTrue

Documents

Visible Light and Its Sources. The Visible Spectrum Light is visible at wavelengths of about 780 nm to 380 nm. We see light as colors, not as waves. Light