3-Light Production - PPT slides

(1)

Luminous Sources

(2)

▪

Non-luminous source

▪

Does not produce

own light

▪

Seen only by using

reflected light

▪

Luminous source

▪

Produces its own light

▪

Example: sun, light

bulb, lit match

(3)

Luminous Sources

▪

Incandescence

▪

Electric discharge

▪

Phosphorescence

▪

Fluorescence

▪

Chemiluminescence

▪

Bioluminescence

▪

Triboluminescence

(4)

Heated tungsten filament glows

Incandescence

▪ Production of light as a result of high temperature

▪ Air from bulb removed and replaced with non-reactive gas

▪ Prevents filament from reacting with oxygen and bursting into flame

▪ _{5-10% of energy converted}

to visible light

▪ Most converted to infrared light (heat)

(5)

Electric Discharge

light production

by passing an

(6)

Electric Discharge

▪ Neon lights = Geissler tubes (1855)

▪ Vacuum pump removed most of the air from a closed tube

▪ Remaining air glowed when an electric current passed through

(7)

Phosphorescence

▪

Light production by the absorption of

UV light

resulting in the emission of

visible light

over an

extended period of time

▪

Objects coated with

phosphors

that absorb

UV

light

. Phosphors keep some of the energy and

over time

release some of the

lower energy

as

visible light

.

(8)

Fluorescence

▪ Light production by the absorption of UV light resulting in immediate emission of visible light

▪ _{Example: fluorescent dyes in detergent,}

(9)

Fluorescent Light

Structure of Fluorescent Lights

▪ _{Light tube filled with low-pressure mercury vapour and an inert gas}

(e.g. Argon)

▪ Inner surface of tube coated with fluorescent material known as phosphors

How Fluorescent lights work (video) http://www.youtube.com/watch?v=ur5yPa4_j3c&NR=1

1. Electric Discharge: Electric current causes Hg atoms to emit UV light 2. Fluorescence: UV light strikes phosphors which convert the energy into

(10)

Fluorescent Light

Pro

▪ Same light output as

incandescent bulb but less heat produced

▪ Uses less electricity for same amount of light

▪ Lasts longer

Con

▪ More expensive than incandescent bulbs

▪ _{Contain mercury and}

(11)

Chemiluminescence

▪

Production of light as the result of a

chemical reaction

(12)

Chemiluminescence

How light sticks work:

▪ One chemical in a

narrow small glass vial

▪ _{Other chemical in main}

body

▪ Bending stick breaks glass vial

▪ _{Chemical mix in the}

main body

(13)

▪ Camping

▪ Law enforcement

▪ Military personnel

▪ _{Entertainment venues} ▪ Emergencies

▪ Underwater divers (source has no moving parts,

completely sealed)

▪ _{Hazardous environments}

where a spark could be

dangerous (source does not require electric current)

(14)

Bioluminescence

▪

Production of light in living organisms as a result

of a chemical reaction

▪

Little to no heat produced

▪

Function: protection from predators, lure prey,

attract mates

▪

Example:

luciferase

enzyme in

fireflies

catalyze

(15)

(16)

(17)

Bioluminescence

▪

Green Fluorescent Protein (GFP)

: exhibits bright

green fluorescence when exposed to blue light

▪

Originally discovered in jelly fish

▪

Now used extensively in research as a marker for

(18)

Triboluminescence

▪ _{Production of light from friction (rubbing), pressure}

(crushing) or mechanical shock (scratching)

▪ Explained by the breaking of chemical bonds in the material

▪ Most often seen in rubbing of certain crystals

▪ _{Also works with Wintergreen hard candy, pulling apart 2}

(19)

Light-emitting

diode (LED)

▪ Production of light by an electric current flowing in a diode

▪ _{Diode: a simple type of}

semiconductors

▪ Semiconductor: a material that allows electric current to flow in only one

direction

(20)

Light-Emitting Diode Comparison

Compared to incandescent bulbs Pros

▪ No filament (doesn’t burn out)

▪ Not much heat production (less wasted energy)

▪ More energy efficient (longer lifespan, lower power usage) Cons

▪ Produces a cool ‘blue’ light

instead of the warm ‘yellow’ light

Compared to compact fluorescent bulbs

Pros

▪ No toxic mercury

▪ More energy efficient (longer lifespan, lower power usage) Cons

(21)

LASER

▪

L

ight

▪

A

mplification by

▪

S

timulated

▪

E

mission of

(22)

▪

Monochromatic

▪

emit wavelengths of the same energy level

▪

results in a light beam of a single pure colour

▪

Directional

▪

light rays travel in the same direction

▪

results in light that is concentrated into one

narrow beam and can travel great distances

without spreading out

▪

Coherent

▪

wave fronts launch in unison

(23)

Application of Lasers

-

Manufacturing:

cutting glass, burning through steel

-

Astronomy:

measure Earth-moon distance

-

Research:

surveyor to measure distance

-

Entertainment:

laser light shows

-

Military:

Boeing airborne laser, tactical high energy laser

(24)

Military Application of Lasers

(25)

Military Application of Lasers

Tactical High

Energy Laser

(THEL)

(video)

(26)

Media Technology Application

▪

CD & DVDs are read by lasers

▪

Pits: bumps on discs that scatter laser light

in all directions

▪

Land: non-bumps that reflect laser light

▪

Reflected light is converted into binary code

(27)

DVD & Blu-Ray

Construction

DVD

Blu-Ray

Laser

Red

Blue

Wavelength 650 nm 405 nm

Pit

0.4 µm

0.15 µm

Track pitch

0.74 µm 0.32 µm

Storage

4.7 GB

25 GB

(video)