understanding led’s 1

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Picking the Correct LED Picking the Correct LED for your designfor your design

by: Philip Levickby: Philip Levick

March 17March 17thth, 2009, 2009

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Overview

Applications for LED’s

Advantages of LED’s

Basic physics behind LED’s

Important terms when picking LED’s

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Applications for LED’sApplications for LED’sSigns

Transportation

Personal Electronics

Lighting

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Advantages to LED’sAdvantages to LED’sPower SavingsPower Savings

Lower HeatLower Heat Incandescent ≈ 17Incandescent ≈ 17m/Wm/W LED ≈ 100LED ≈ 100m/Wm/W

LifeLife Incandescent ≈ 1000hrs.Incandescent ≈ 1000hrs. LED ≈ 50,000hrs.LED ≈ 50,000hrs.

Small form factorSmall form factor

DurabilityDurability

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Basic Physics behind LED’sBasic Physics behind LED’s

Semiconductor materials are picked

Electrons and Holes are excited by a forward Current

Electrons and holes are combined Excess energy is emitted as photons

The distance the electron falls determines the wavelength

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Basic Physics behind LED’sBasic Physics behind LED’s

Hole Electron

P-Type N-Type

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

What are the different parts of What are the different parts of the LED?the LED?

Anode

Lead

Frame

Semiconductor

Epoxy Case

Cathode

Wire Bond

Reflector

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Important Definitions

Luminous Flux Measure of power perceived by the eye

Units = lumens (lm) = cd * 1 steradian Steradian

Spherical Area

Luminous Intensity The measure of wavelength emitted power by

a light source in the visible spectrumUnits = candela (cd)

Viewing Angle Angle at which the light is 50% intensity

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Definitions in motion

Viewing Angle = Max Luminous Intensity (cd) * 50%

Luminous intensity = Point source of lightLuminous Flux = Sensitivity to the human eye

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Power Angle

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

How do I choose the LED color?How do I choose the LED color?

Chromaticity diagram

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Chromaticity for a white LED

Chromaticity diagram for white LED

Coordinates for color ranking

b1

b2

a0

c0

X=0.3

Y=0.3

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Summary

Applications for LED’s

Advantages of LED’s

Basic physics of the LED

Important terms when picking LED’s

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

References

LEDlight.com

Nichia.com

Wikipedia.com

Howstuffworks.com

Led.linear1.org

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

Questions

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Backup

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What color is my LED?What color is my LED?

04/10/2304/10/23 Phil Levick - Understanding LED'sPhil Levick - Understanding LED's

b1

b2

a0

c0

X=0.3

Y=0.3