Name: Jamaal Merriweather
Project Advisor: Dr. Moore
Section: RPY
Group Name: The Colors of Sound
Light Emitting Diodes and their Visual Effects
Introduction
Light emitting diode (LED) technology is constantly improving and is now being designed with
reduced wattages and increased lifespans. As a result, LEDs are mainly used in applications such as
traffic lights, street lights, and refrigerators for longer life spans. Reduced wattage will decrease LED
disposal and energy consumption. This technical review paper will describe various commercial
applications of LEDs, explain the operation and visual effect capabilities of a light emitting diode, and
briefly summarize the power considerations and hardware needed to implement this technology.
Commercial Applications of LEDs
General Electric
General Electric (GE) has designed a product known as the “GE LED PAR20 Lamp”; this LED
lamp is more energy-efficient, cost-effective, has a longer lifespan, and is more environmentally
conscious than any other lighting options, such as incandescent and halogen lightbulbs [1]. GE has
ensured that there will be less pollution for power generation by designing the GE LED PAR20 Lamp to
be environmentally conscious. Furthermore, the PAR20 requires 7 watts to operate over a lifespan of
20,000 hours while incandescent and halogen lightbulbs require 30 and 50 watts, respectively [2]. The
LED lamp initially costs $38; however, approximately $14 worth of energy will be consumed after
20,000 hours, which leads to a $2 labor cost to replace the diode lamp [2]. Therefore, the GE LED
PAR20 Lamp will cost approximately $54 to operate with a lifespan of 20,000 hours, assuming that each
kilowatt-hour (kWh) is $0.10 each.
Quantum Devices, Inc.
Quantum Devices, Inc. developed a product for NASA known as the Warfighter’s Accelerated
Recovery by Photobiomodulation (WARP) 10; the WARP 10 is a hand-held LED unit that increases
blood circulation, alleviates muscle pain, and relieves stiffness [3]. Biologists at Quantum Devices, Inc.
stated that cells will grow 150% to 200% faster when exposed to near-infrared light because the intensity
of the light will stimulate the energy process of the mitochondria of each cell, thus expediting the healing
process [3]. According to the engineers at NASA, the WARP 10 device was supposed to be used by the
armed forces for immediate first aid, increasing the soldiers’ endurance in battle. Now, the WARP 10 can
be purchased by anyone for $575.95 or $670.90 (includes eight AA batteries and battery charger) [3].
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Underlying Technology of LEDs
LEDs operate when electrons in the conduction band and holes in the valence band recombine,
causing the excess energy of the electron to be released as photons (light), phonons (heat), or both; the
random excess energy being emitted is known as spontaneous emission [4]. LEDs connected in series
will extend battery life because the same current will light multiple diodes. Light emitting diodes
connected in parallel, however, must each have a resistor attached, or the lowest voltage LED will be
destroyed by the current [5]. The diodes only work in direct bandgap semiconductors such as Gallium
arsenide (GaAs) and Indium phosphide (InP) because photons do not have enough momentum to go
sideways or diagonally across the bandgap; photons can only make vertical transitions across the bandgap
[4]. Colored LEDs with high intensity tend to enhance the visual effects of an electronic appliance; a
higher luminous intensity will enhance the brightness of the diode at a given current [5]. Light emitting
diodes are available in the following colors: blue, green, yellow, orange, and red; these colors correspond
to a wavelength range of approximately 475-700 nanometers on the electromagnetic spectrum [4], [5].
Implementation of LEDs
Typical standard LEDs will have a power dissipation of approximately 100 milliwatts, whereas
newer diode models, such as high power light emitting diode lamps, will have a power dissipation of
approximately 5 watts or more [6]. As power dissipation increases, the luminous intensity, cost, and heat
dissipation will also increase. Nevertheless, multiple low-power LEDs instead of one high power diode
lamp can achieve the same amount of luminous intensity while minimizing heat dissipation [7].
According to [8], the voltage-current characteristics of the standard blue light emitting diode has a
maximum forward voltage of 4 volts at 20 milliamps, which is equivalent to 80 milliwatts; however, [5]
states that the high intensity blue LED has a maximum forward voltage of 5.5 volts at 30 milliamps,
which equals to 165 milliwatts. Because the standard blue light emitting diode has lower power
dissipation than the high intensity blue diode, the latter LED is much brighter, but unfortunately, more
expensive. Light emitting diodes can be implemented using the standard through-pin diode or as surface
mount packages (SMDs). According to [6], SMDs dissipate heat more efficiently than the conventional
through-pin light emitting diodes; furthermore, surface mount packages are brighter and easier to
assemble, but more expensive, than the standard through-pin LEDs.
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Name: Jamaal Merriweather
Project Advisor: Dr. Moore
[1]
Section: RPY
Group Name: The Colors of Sound
General Electric Company, “General Lighting,” 2010. [Online]. Available:
http://www.gelighting.com/na/business_lighting/products/led/general_lighting.htm [Accessed:
Jan 23, 2010].
[2]
General Electric Company. (2009, April). [Online]. Available:
http://www.gelighting.com/na/business_lighting/education_resources/literature_library/sell_sheet
s/downloads/led/LED-PAR20_Sell_sheet-74440.pdf
[3]
“Warp Light Therapy,” warplighttherapy.com, 2006. [Online]. Available:
http://www.warplighttherapy.com/WARP10_ProductsPage.htm. [Accessed: Jan 23, 2010].
[4]
B.L Anderson and R.L Anderson, “Optoelectronic Devices,” in Fundamentals of Semiconductor
Devices. New York: McGraw-Hill, 2005, ch.11, sec.3, pp. 692-701.
[5]
J. Hewes, “Light Emitting Diodes (LEDs),” kpsec.freeuk.com, 2009. [Online]. Available:
http://www.kpsec.freeuk.com/components/led.htm. [Accessed Jan 23, 2010].
[6]
Lunar Accents Design, “Light Emitting Diodes,” lunaraccents.com, para.1, 2008. [Online].
Available: http://www.lunaraccents.com/design-light-emitting-diodes.html. [Accessed: Jan 24,
2010].
[7]
T.Y. Wu, “Light-Emitting-Diode Lamp,” U.S. Patent 7 585 090, Sep 8, 2009.
[8]
A. Chakraborty, T.J. Baker, B.A. Haskell, F. Wu, J.S. Speck, S.P. Denbaars, S. Nakamura, and
U.K. Mishra. (2005). “Milliwatt power blue InGaN/GaN light emitting diodes on semipolar GaN
templates.” Japanese Journal of Applied Physic, Part 2: Letters [Online]. 44(28-32), L945L947. Available:
http://www.engineeringvillage.com.www.library.gatech.edu:2048/controller/servlet/Controller?S
EARCHID=1f217ec126406b36aa3d02prod4data1&CID=expertSearchDetailedFormat&DOCIN
DEX=2&database=1&format=expertSearchDetailedFormat
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