Luminous efficacy

Lm/W

1

Lm/W

2

Luminous efficacy (LE)

Lm/W

3

Luminous efficacy (LE)

4

Lab record – CREE303 lum/watt

IKEAPHILIPS

NICHIA

Luminous efficacy (LE)

Fluorescent lighting threshold

DoE

5

Long life up to and beyond 20,000

hours. lifetime –

The energy consumed by one

LED is the equivalent of 50 halogen bulbs.

LEDs offer greater color mixing.

Combined with compact size, offers wide range of design

options.

Compact sizeLong life

Shock resistantInstant on/off

LEDs are more energy efficient.

Coupled with longevity, LED bulbs

= fewer lamps required to be

disposed of.

LOW-COST PERFORMANCE TECHNICAL ENVIRONMENTAL

LED

6

LED

7

°1907 – SiC – yellow emission

1940s: theoretical framework (cfr. transistor, p-n junction)

1955: EL in III-V compounds

1962: IR emission in GaAs (+ laser)

1960s: green and red LEDs based on GaP

Blue: predicted in GaN-based LEDs in 1950sRealized in 1994 – Nobel Prize in 2014

LEDs –

8

LED

9

LED

10

11

White LED GaN or InGaN LED Ce:YAG

12

13

Il Laser

• Caratteristiche• Coerenza• Alta intensita’• Alta direzionalita’• Alta

monocromaticita’

§ Parti principali§ Mezzo attivo§ Metodi di pompaggio§ Cavita’ di risonanza

14

𝐼 = 𝐼!𝑒" #!$#" % Se N2>N1 l'intensità aumenta

𝐼𝐼!= 𝑒"($) 𝐺 𝜈 = 2𝜎 𝑁& − 𝑁' 𝐿

𝛾 𝑓𝑎𝑡𝑡𝑜𝑟𝑒 𝑑𝑖 𝑝𝑒𝑟𝑑𝑖𝑡𝑎𝐼𝐼!= 𝑒" $ () $ 𝐺 > 𝛾 𝑠𝑒 𝑁& − 𝑁' >

𝛾2𝜎𝐿

15

Cavità risonante

𝑛 𝜈 𝑑𝜈 =8𝜋𝜈&

𝑐*Densita’ dei modi di radiazione termica (onde stazionarie in cavita’)

Lo scopo della cavita’ e’ quello di concentrare la radiazione emessa in un numero ridotto di modi in maniera da aumentare il numero di fotoni per ciascuno di tali modi.

G(n)

n16