Light Emitting Diode
This document was uploaded by user and they confirmed that they have the permission to share it. If you are author or own the copyright of this book, please report to us by using this DMCA report form. Report DMCA
Overview
Download & View Light Emitting Diode as PDF for free.
More details
- Words: 1,851
- Pages: 13
P age |1 LIGHT EMITTING DIODE Technical LED's LED Color Chart
Wavelength (nm)
Color Name
Fwd Voltage (Vf @ 20ma)
Intensity 5mm LEDs
Viewing Angle
940
Infrared
1.5
16mW @50mA
15°
880
Infrared
1.7
18mW @50mA
15°
850
Infrared
1.7
26mW @50mA
15°
660
Ultra Red
1.8
2000mcd @50mA
15°
635
High Eff. Red
2.0
200mcd @20mA
15°
633
Super Red
2.2
3500mcd @20mA
15°
620
Super Orange
2.2
4500mcd @20mA
15°
612
Super Orange
2.2
6500mcd @20mA
15°
605
Orange
2.1
160mcd @20mA
15°
595
Super Yellow
2.2
5500mcd @20mA
15°
592
Super Pure Yellow
2.1
7000mcd @20mA
15°
585
Yellow
2.1
100mcd @20mA
15°
3.6
2000mcd @20mA
20°
3.6
4000mcd @20mA
20°
4500K 6500K
"Incandescent" White Pale White
8000K
Cool White
3.6
6000mcd @20mA
20°
574
Super Lime Yellow
2.4
1000mcd @20mA
15°
570
Super Lime Green
2.0
1000mcd @20mA
15°
565
High Efficiency Green
2.1
200mcd @20mA
15°
560
Super Pure Green
2.1
350mcd @20mA
15°
555
Pure Green
2.1
80mcd @20mA
15°
525
Aqua
3.5
10,000mcd
15°
LED Dye Material GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Aluminum Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Aluminum Arsenide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide SiC/GaN -- Silicon Carbide/Gallium Nitride SiC/GaN -- Silicon Carbide/Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaP/GaP - Gallium Phosphide/Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaP/GaP - Gallium Phosphide/ Gallium Phosphide SiC/GaN - Silicon
P age |2 Green
@20mA
505
Blue Green
3.5
2000mcd @20mA
45°
470
Super Blue
3.6
3000mcd @20mA
15°
430
Ultra Blue
3.8
100mcd @20mA
15°
Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride
Relative Intensity vs Wavelength (P)
Forward Current vs Forward Voltage Red 5, Ultra Red 4, HE Red 6, Orange 7, Bright Red 3, HE Green 9, Yellow 8
Forward Current vs Ambient Air Temperature Red 5, Ultra Red 4, HE Red 6, Orange 7, HE Green 9, Ultra Blue D, Yellow 8, Bright Red 3
Relative Luminous Intensity vs Forward Current Ultra Red 4, HE Red 6, Orange 7, Yellow 8, HE Green 9 Red 5, Bright Red 3, Pure Blue C
Relative Luminous Intensity vs Ambient Temperature Red 5, Bright Red 3, Ultra Red 4, HE Green 9, Yellow 8
P age |3
Maximum Tolerable Peak Current vs Pulse Duration Ultra Red, Red, HE Red, Orange, Yellow, HE Green, Ultra Green (523nm), Ultra Green (502nm), Pure Blue, Ultra Blue
Bright Red
Page |4 Light Emitting diode (LED ) A light-emitting-diode (LED)) is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit.. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction. Electroluminescence devices that are composed of semiconductor materials that are capable of generating light when they are forward biased by a current source. The center wavelength of an LED device is determined by the band gap energy in eV at the active layer given Semiconductor materials:
.
=
------ ---- (1)
P age |5
P age |6 Basic Diagram of LED
P age |7 Physical principles The inner workings of an LED
I-V diagram for a diode an LED will begin to emit light when the on-voltage is exceeded. Typical on voltages are 2-3 Volt Like a normal diode, the LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to nearinfrared, visible or near-ultraviolet light. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.
P age |8 Light extraction The refractive index of most LED semiconductor materials is quite high, so in almost all cases the light from the LED is coupled into a much lower-index medium. The large index difference makes the reflection quite substantial (per the Fresnel coefficients). The produced light gets partially reflected back into the semiconductor, where it may be absorbed and turned into additional heat; this is usually one of the dominant causes of LED inefficiency. Often more than half of the emitted light is reflected back at the LED-package and package-air interfaces. The reflection is most commonly reduced by using a dome-shaped (half-sphere) package with the diode in the center so that the outgoing light rays strike the surface perpendicularly, at which angle the reflection is minimized. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should also match the index of the semiconductor, to minimize back-reflection. An anti-reflection coating may be added as well. The package may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted.
•
Power ranging from .05mW to 2 mW. Chromatic chart and angle of emission
Page |9
Angle of emission
Radiation Plot Follow the Lambertian surface emission plot. LED characteristic
Power Efficiency
Internal Power Efficiency
External Power Efficiency
a : Internal Power Efficiency ratio of photons generated to the number of electron induced into the active layer of the device
P a g e | 10
!
− − − − − − 2
B: External Power Efficiency Ratio of the optical power couple into the fiber to the electrical power applied by the optical device. %& '(
')!
**
+++++++++ ,
Where optical power PF is only a fraction of the power generated internally by the optical device. This optical power loss is relevant to the device optical fiber coupling efficiency expressed as -. − − − − − − − − − 4
A maximum power couple into the optical fiber is given by 01234 5* .267 8 -.
− − − − − − − − 5
Where I0 is the ratio of the source optical power output and active area. LED spectral Bandwidth at the half power point The LED spectral bandwidth determine the half power point of the spectral density in reference to wavelength .
LED Bandwidth : LED are intensity modulated devices, that is input current can directly affect the output intensity of the device. In digital device the time delay b/w ON and OFF of LED is determine by the rise time and fall time of LED source. Rise time is measured between 10% and 90% of the power output. Fall time is the time it takes the output power to decrease from 90% to 10 %.
P a g e | 11 These time gives us information about the maximum data bit rate the device is capable of handling. These time delays are due to carrier recombination and change of capacitance. The total optical bandwidth at the half power point is given by
:; <=
− − − − − − 6
Where r is the carrier lifetime or carrier recombination. :?
*.,@ A )B )C
− − − − − − 7
Lambertian Surface Lambert's cosine law in optics says that the radiant intensity observed from a "Lambertian" surface is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal. The law is also known as the cosine emission law or Lambert's emission law. It is named after Johann Heinrich Lambert, from his Photometria, published in 1760. An important consequence of Lambert's cosine law is that when such a surface is viewed from any angle, it has the same apparent radiance. This means, for example, that to the human eye it has the same apparent brightness (or luminance). It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the size of the observed area is increased by a corresponding amount, so that while the area element appears the same in reality it has increased by the cosine of the angle and therefore its radiance is the same. For example, in the visible spectrum, the Sun is almost a perfect Lambertian radiator, and as a result the brightness of the Sun is almost the same everywhere on an image
P a g e | 12
UVWXY Z[\
Couple in fiber laws Butt Method
Lens Method
Butt Method(direct (direct coupling) fundamental requirement is cross section of fiber is equal to the optical source. E FG
]
^ 7 2HI6J2 2HI6J2 `6aH= 37I _
bcJ=H
4
h
u t d efg ehi g − − − − − 8
-. t F op q r1 − eug vw LMNOPQRKS klmQnP K LMNOPQRKS 9 E − − − 9 u t pq2
Lens Method
Source behind the focal point of lense
source infront of focal point of lense
LED Reliability and operational Lifetime Maximum LED operational time is T1 :1 F1 y1 z1 e {|) } g ~~
+++++++
Where BF = base failure rate , TF = temperature factor , EF = environmental factor, QF = quality factor.
P a g e | 13 The mean time between failure (MTBF) is F:
(
The BF = 6.5 x 10-4 Now F
1&.* 4 *~ H
~~~ ) +++++++ *
F] q ] 0I
− − − − − − 11
Where θJA = thermal resistance, Pd is the thermal dissipation of power. TA is ambient temperature. 0I 51 1
Wavelength (nm)
Color Name
Fwd Voltage (Vf @ 20ma)
Intensity 5mm LEDs
Viewing Angle
940
Infrared
1.5
16mW @50mA
15°
880
Infrared
1.7
18mW @50mA
15°
850
Infrared
1.7
26mW @50mA
15°
660
Ultra Red
1.8
2000mcd @50mA
15°
635
High Eff. Red
2.0
200mcd @20mA
15°
633
Super Red
2.2
3500mcd @20mA
15°
620
Super Orange
2.2
4500mcd @20mA
15°
612
Super Orange
2.2
6500mcd @20mA
15°
605
Orange
2.1
160mcd @20mA
15°
595
Super Yellow
2.2
5500mcd @20mA
15°
592
Super Pure Yellow
2.1
7000mcd @20mA
15°
585
Yellow
2.1
100mcd @20mA
15°
3.6
2000mcd @20mA
20°
3.6
4000mcd @20mA
20°
4500K 6500K
"Incandescent" White Pale White
8000K
Cool White
3.6
6000mcd @20mA
20°
574
Super Lime Yellow
2.4
1000mcd @20mA
15°
570
Super Lime Green
2.0
1000mcd @20mA
15°
565
High Efficiency Green
2.1
200mcd @20mA
15°
560
Super Pure Green
2.1
350mcd @20mA
15°
555
Pure Green
2.1
80mcd @20mA
15°
525
Aqua
3.5
10,000mcd
15°
LED Dye Material GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Aluminum Arsenide GaAIAs/GaAs -- Gallium Aluminum Arsenide/Gallium Aluminum Arsenide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaAsP/GaP - Gallium Arsenic Phosphide / Gallium Phosphide SiC/GaN -- Silicon Carbide/Gallium Nitride SiC/GaN -- Silicon Carbide/Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride InGaAIP - Indium Gallium Aluminum Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaP/GaP - Gallium Phosphide/Gallium Phosphide InGaAIP - Indium Gallium Aluminum Phosphide GaP/GaP - Gallium Phosphide/ Gallium Phosphide SiC/GaN - Silicon
P age |2 Green
@20mA
505
Blue Green
3.5
2000mcd @20mA
45°
470
Super Blue
3.6
3000mcd @20mA
15°
430
Ultra Blue
3.8
100mcd @20mA
15°
Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride SiC/GaN - Silicon Carbide / Gallium Nitride
Relative Intensity vs Wavelength (P)
Forward Current vs Forward Voltage Red 5, Ultra Red 4, HE Red 6, Orange 7, Bright Red 3, HE Green 9, Yellow 8
Forward Current vs Ambient Air Temperature Red 5, Ultra Red 4, HE Red 6, Orange 7, HE Green 9, Ultra Blue D, Yellow 8, Bright Red 3
Relative Luminous Intensity vs Forward Current Ultra Red 4, HE Red 6, Orange 7, Yellow 8, HE Green 9 Red 5, Bright Red 3, Pure Blue C
Relative Luminous Intensity vs Ambient Temperature Red 5, Bright Red 3, Ultra Red 4, HE Green 9, Yellow 8
P age |3
Maximum Tolerable Peak Current vs Pulse Duration Ultra Red, Red, HE Red, Orange, Yellow, HE Green, Ultra Green (523nm), Ultra Green (502nm), Pure Blue, Ultra Blue
Bright Red
Page |4 Light Emitting diode (LED ) A light-emitting-diode (LED)) is a semiconductor diode that emits light when an electric current is applied in the forward direction of the device, as in the simple LED circuit.. The effect is a form of electroluminescence where incoherent and narrow-spectrum light is emitted from the p-n junction. Electroluminescence devices that are composed of semiconductor materials that are capable of generating light when they are forward biased by a current source. The center wavelength of an LED device is determined by the band gap energy in eV at the active layer given Semiconductor materials:
.
=
------ ---- (1)
P age |5
P age |6 Basic Diagram of LED
P age |7 Physical principles The inner workings of an LED
I-V diagram for a diode an LED will begin to emit light when the on-voltage is exceeded. Typical on voltages are 2-3 Volt Like a normal diode, the LED consists of a chip of semiconducting material impregnated, or doped, with impurities to create a p-n junction. As in other diodes, current flows easily from the p-side, or anode, to the n-side, or cathode, but not in the reverse direction. Charge-carriers—electrons and holes—flow into the junction from electrodes with different voltages. When an electron meets a hole, it falls into a lower energy level, and releases energy in the form of a photon. The wavelength of the light emitted, and therefore its color, depends on the band gap energy of the materials forming the p-n junction. In silicon or germanium diodes, the electrons and holes recombine by a non-radiative transition which produces no optical emission, because these are indirect band gap materials. The materials used for the LED have a direct band gap with energies corresponding to nearinfrared, visible or near-ultraviolet light. LED development began with infrared and red devices made with gallium arsenide. Advances in materials science have made possible the production of devices with ever-shorter wavelengths, producing light in a variety of colors. LEDs are usually built on an n-type substrate, with an electrode attached to the p-type layer deposited on its surface. P-type substrates, while less common, occur as well. Many commercial LEDs, especially GaN/InGaN, also use sapphire substrate.
P age |8 Light extraction The refractive index of most LED semiconductor materials is quite high, so in almost all cases the light from the LED is coupled into a much lower-index medium. The large index difference makes the reflection quite substantial (per the Fresnel coefficients). The produced light gets partially reflected back into the semiconductor, where it may be absorbed and turned into additional heat; this is usually one of the dominant causes of LED inefficiency. Often more than half of the emitted light is reflected back at the LED-package and package-air interfaces. The reflection is most commonly reduced by using a dome-shaped (half-sphere) package with the diode in the center so that the outgoing light rays strike the surface perpendicularly, at which angle the reflection is minimized. Substrates that are transparent to the emitted wavelength, and backed by a reflective layer, increase the LED efficiency. The refractive index of the package material should also match the index of the semiconductor, to minimize back-reflection. An anti-reflection coating may be added as well. The package may be colored, but this is only for cosmetic reasons or to improve the contrast ratio; the color of the packaging does not substantially affect the color of the light emitted.
•
Power ranging from .05mW to 2 mW. Chromatic chart and angle of emission
Page |9
Angle of emission
Radiation Plot Follow the Lambertian surface emission plot. LED characteristic
Power Efficiency
Internal Power Efficiency
External Power Efficiency
a : Internal Power Efficiency ratio of photons generated to the number of electron induced into the active layer of the device
P a g e | 10
!
− − − − − − 2
B: External Power Efficiency Ratio of the optical power couple into the fiber to the electrical power applied by the optical device. %& '(
')!
**
+++++++++ ,
Where optical power PF is only a fraction of the power generated internally by the optical device. This optical power loss is relevant to the device optical fiber coupling efficiency expressed as -. − − − − − − − − − 4
A maximum power couple into the optical fiber is given by 01234 5* .267 8 -.
− − − − − − − − 5
Where I0 is the ratio of the source optical power output and active area. LED spectral Bandwidth at the half power point The LED spectral bandwidth determine the half power point of the spectral density in reference to wavelength .
LED Bandwidth : LED are intensity modulated devices, that is input current can directly affect the output intensity of the device. In digital device the time delay b/w ON and OFF of LED is determine by the rise time and fall time of LED source. Rise time is measured between 10% and 90% of the power output. Fall time is the time it takes the output power to decrease from 90% to 10 %.
P a g e | 11 These time gives us information about the maximum data bit rate the device is capable of handling. These time delays are due to carrier recombination and change of capacitance. The total optical bandwidth at the half power point is given by
:; <=
− − − − − − 6
Where r is the carrier lifetime or carrier recombination. :?
*.,@ A )B )C
− − − − − − 7
Lambertian Surface Lambert's cosine law in optics says that the radiant intensity observed from a "Lambertian" surface is directly proportional to the cosine of the angle θ between the observer's line of sight and the surface normal. The law is also known as the cosine emission law or Lambert's emission law. It is named after Johann Heinrich Lambert, from his Photometria, published in 1760. An important consequence of Lambert's cosine law is that when such a surface is viewed from any angle, it has the same apparent radiance. This means, for example, that to the human eye it has the same apparent brightness (or luminance). It has the same radiance because, although the emitted power from a given area element is reduced by the cosine of the emission angle, the size of the observed area is increased by a corresponding amount, so that while the area element appears the same in reality it has increased by the cosine of the angle and therefore its radiance is the same. For example, in the visible spectrum, the Sun is almost a perfect Lambertian radiator, and as a result the brightness of the Sun is almost the same everywhere on an image
P a g e | 12
UVWXY Z[\
Couple in fiber laws Butt Method
Lens Method
Butt Method(direct (direct coupling) fundamental requirement is cross section of fiber is equal to the optical source. E FG
]
^ 7 2HI6J2 2HI6J2 `6aH= 37I _
bcJ=H
4
h
u t d efg ehi g − − − − − 8
-. t F op q r1 − eug vw LMNOPQRKS klmQnP K LMNOPQRKS 9 E − − − 9 u t pq2
Lens Method
Source behind the focal point of lense
source infront of focal point of lense
LED Reliability and operational Lifetime Maximum LED operational time is T1 :1 F1 y1 z1 e {|) } g ~~
+++++++
Where BF = base failure rate , TF = temperature factor , EF = environmental factor, QF = quality factor.
P a g e | 13 The mean time between failure (MTBF) is F:
(
The BF = 6.5 x 10-4 Now F
1&.* 4 *~ H
~~~ ) +++++++ *
F] q ] 0I
− − − − − − 11
Where θJA = thermal resistance, Pd is the thermal dissipation of power. TA is ambient temperature. 0I 51 1
Related Documents
Light Emitting Diode
June 2020 2
Light Emitting Polymer
June 2020 2
Light Emitting Diodes
June 2020 1
Light Emitting Polymer
May 2020 2
Light Emitting Polymers
November 2019 4