Book LightBook Light

Light Emitting Diode

2 - AAA Batteries

Push Button Switch

Circuit DiagramCircuit Diagram

LED DiodeLED Diode

Diode is a one-way electrical switch that Diode is a one-way electrical switch that passes current in one direction.passes current in one direction.

The LED emits light of a certain The LED emits light of a certain wavelength (i.e. color)wavelength (i.e. color)

Constructed with a semiconductor materialConstructed with a semiconductor material

A semiconductor is a material that in it A semiconductor is a material that in it pure form does not conduct electricity pure form does not conduct electricity well.well.

Silicon is a common semiconductor with Silicon is a common semiconductor with four electrons in its outer shell.four electrons in its outer shell.

A silicon atom shares electrons with four A silicon atom shares electrons with four neighboring atoms allowing the outer shell neighboring atoms allowing the outer shell to be filled completely.to be filled completely.

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By substituting some of the Silicon with atoms By substituting some of the Silicon with atoms that have five (instead of four) outer electrons, that have five (instead of four) outer electrons, there are electrons left over to roamthere are electrons left over to roam

By substituting some of the Silicon with atoms By substituting some of the Silicon with atoms that have three outer electrons there are that have three outer electrons there are ‘holes’ created.‘holes’ created.

Negatively doped Silicon

Positively doped Silicon

P-type Dopant N-type Dopant

Electrons and holes are pushed toward Electrons and holes are pushed toward junction when a positive voltage is applied junction when a positive voltage is applied

to the P-sideto the P-side

At the junction, Electrons and Holes At the junction, Electrons and Holes recombinedrecombined

Energy in the form of light is Energy in the form of light is given off when an electron and given off when an electron and

hole combine.hole combine.

A roaming electron has more energy than an electron A roaming electron has more energy than an electron bound to an atom (in a hole). That energy is given off as bound to an atom (in a hole). That energy is given off as light.light.

Electrons and holes swept away from junction Electrons and holes swept away from junction when a negative voltage is applied to the P-side, when a negative voltage is applied to the P-side,

so no current flows in circuitso no current flows in circuit

What makes the light white?What makes the light white? LEDs usually emit one wavelength LEDs usually emit one wavelength

(color) of light.(color) of light. Most White LEDs use a blue LED Most White LEDs use a blue LED

(GaN) covered with a yellow phosphor (GaN) covered with a yellow phosphor coating. The yellow mixed with blue coating. The yellow mixed with blue appears white.appears white.

A phosphor material emits light when exposed to radiation. In this case the phosphor is “excited” by the blue light and in turn emits yellow light.

Pre-assessment #4Pre-assessment #4 How does a LED and diode work?How does a LED and diode work? Next two tests (review updated schedule)Next two tests (review updated schedule) Oral presentationsOral presentations Book ReportBook Report Bring CDs and music sources (MP3s, etc.) on Bring CDs and music sources (MP3s, etc.) on

MondayMonday Other motors (4-pole, reed switch)Other motors (4-pole, reed switch) Makes sure and pick up graded stuffMakes sure and pick up graded stuff Get handoutsGet handouts Speakers, recording sounds, transmitting Speakers, recording sounds, transmitting

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