Assignment 2 LED info
From Physical Programming
Light-emitting diode
A light-emitting diode (LED) is an electronic light source. The LED was found and discovered in the early 20th century, but it wasn’t until 1962 that it became a practical electronic component. All early devices emitted low-intensity red light, but modern LEDs are available across the visible, ultraviolet and infra red wavelengths, with very high brightness.
LEDs are based on the semiconductor diode. When the diode is forward biased (switched on), electrons are able to recombine with holes and energy is released in the form of light. This effect is called electroluminescence and the color of the light is determined by the energy gap of the semiconductor. The LED is usually small in area (less than 1 mm2) with integrated optical components to shape its radiation pattern and assist in reflection.
LEDs present many advantages over traditional light sources including lower energy consumption, longer lifetime, improved robustness, smaller size and faster switching. However, they are relatively expensive and require more precise current and heat management than traditional light sources.
Applications of LEDs are diverse. They are used as low-energy replacements for traditional light sources in well-established applications such as indicators and automotive lighting. The compact size of LEDs has allowed new text and video displays and sensors to be developed, while their high switching rates are useful in communications technology.
How it works
Light is a form of energy that can be released by an atom. It is made up of many small particle-like packets that have energy and momentum but no mass. These particles, called photons, are the most basic units of light. Photons are released as a result of moving electrons. In an atom, electrons move in orbitals around the nucleus. Electrons in different orbitals have different amounts of energy. Generally speaking, electrons with greater energy move in orbitals farther away from the nucleus.
History
Discoveries and early devices
• Oleg Losev created one of the first LEDs in the mid 1920s
• Electroluminescence was discovered in 1907 by the British experimenter H. J. Round of Marconi Labs, using a crystal of silicon carbide and a cat's-whisker detector.
• Russian Oleg Vladimirovich Losev independently created the first LED in the mid 1920s; his research was distributed in Russian, German and British scientific journals, but no practical use was made of the discovery for several decades.
• Rubin Braunstein of the Radio Corporation of America reported on infrared emission from gallium arsenide (GaAs) and other semiconductor alloys in 1955.
• In 1961, experimenters Bob Biard and Gary Pittman working at Texas Instruments, found that GaAs emitted infrared radiation when electric current was applied and received the patent for the infrared LED.
• The first practical visible-spectrum (red) LED was developed in 1962 by Nick Holonyak Jr., while working at General Electric Company.
• Holonyak is seen as the "father of the light-emitting diode".
• Up to 1968 visible and infrared LEDs were extremely costly, on the order of US $200 per unit
• Hewlett Packard (HP) introduced LEDs in 1968
Uses -Automotive head lamps
- Lights and signs
-Modern traffic lights
-Ship lanterns
- Aircraft cockpits
- Submarine and ship bridges
-Astronomy observatories
-Night time animal watching
-Military field use.
-High mounted truck and bus lights
-Flashlights
-Grow lights using LEDs to increase photosynthesis in plants
-Remote controls, such as for TVs and VCRs, often use infrared LEDs.
-Movement sensors, for example in optical computer mice. The Nintendo Wii's sensor bar uses infrared LED
-In optical fiber and Free Space Optics communications.
-In pulse oximeters for measuring oxygen saturation
-Some flatbed scanners
Parts of an LED:
Life time and failure Solid state devices such as LEDs are subject to very limited wear and tear if operated at low currents and at low temperatures. Many of the LEDs produced in the 1970s and 1980s are still in service today. Typical lifetimes quoted are 25000 to 100000 hours but heat and current settings can extend or shorten this time significantly. Colors and materials Conventional LEDs are made from a variety of inorganic semiconductor materials, the following table shows the available colors with wavelength range, voltage drop and material: Color Wavelength [nm] Voltage [V] Semiconductor Material Infrared λ > 760 ΔV < 1.9 Gallium arsenide (GaAs) Aluminium gallium arsenide (AlGaAs)
Red 610 < λ < 760 1.63 < ΔV < 2.03 Aluminium gallium arsenide (AlGaAs) Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Orange 590 < λ < 610 2.03 < ΔV < 2.10 Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Yellow 570 < λ < 590 2.10 < ΔV < 2.18 Gallium arsenide phosphide (GaAsP) Aluminium gallium indium phosphide (AlGaInP) Gallium(III) phosphide (GaP)
Green 500 < λ < 570 2.18 < ΔV < 4.0 Indium gallium nitride (InGaN) / Gallium(III) nitride (GaN) Gallium(III) phosphide (GaP) Aluminium gallium indium phosphide (AlGaInP) Aluminium gallium phosphide (AlGaP)
Blue 450 < λ < 500 2.48 < ΔV < 3.7 Zinc selenide (ZnSe) Indium gallium nitride (InGaN) Silicon carbide (SiC) as substrate Silicon (Si) as substrate — (under development)
Violet 400 < λ < 450 2.76 < ΔV < 4.0 Indium gallium nitride (InGaN)
Purple multiple types 2.48 < ΔV < 3.7 Dual blue/red LEDs, blue with red phosphor, or white with purple plastic Ultraviolet λ < 400 3.1 < ΔV < 4.4 diamond (C) Aluminium nitride (AlN) Aluminium gallium nitride (AlGaN) Aluminium gallium indium nitride (AlGaInN) — (down to 210 nm[25])
White Broad spectrum ΔV = 3.5 Blue/UV diode with yellow phosphor
Types of LEDs
LEDs are produced in an array of shapes and sizes. The 5 mm cylindrical package (red, fifth from the left) is the most common. The color of the plastic lens is often the same as the actual color of light emitted, but this is not always the case. Miniature LEDs
Different sized LEDs. 8 mm, 5 mm and 3 mm, with a wooden match-stick for scale.
These are mostly single-die LEDs used as indicators, and they come in various-sizes from 2 mm to 8 mm, through-hole and surface mount packages. They are usually simple in design, not requiring any separate cooling body. Typical current ratings ranges from around 1 mA to above 20 mA. The small scale set a natural upper boundary on power consumption due to heat caused by the high current density and need for heat sinking.
Advantages
• Efficiency:
• Color:
• Size:
• On/Off time:
• Cycling:
• Dimming:
• Cool light:
• Slow failure:
• Lifetime:
• Shock resistance:
• Focus:
• Toxicity:
Disadvantages
• High price
• Temperature dependence
• Voltage sensitivity
• Light quality
• Area light source: LEDs do not approximate a “point source” of light
• Blue Hazard
• Blue pollution
