Abstract
Light Emitting Diode (LED) is a semiconductor that emits light when electrical
current flows through the diode, causing electrons and holes to meet at the
same part of the semiconductor, called the junction. When the electrons fill
the holes, energy is released in the form of light. Currently, white LED is
being incorporated into a variety of applications including flat panel display
(FPD) backlights, automotive lamps, general lighting, etc. and its use is
growing.
White LEDs have several advantages over incandescent and fluorescent lighting.
One advantage is the lack of mercury, a poisonous material that is harmful to
the environment and banned by the RoHS directive. Although fluorescent
lighting has been used for its power saving benefits, almost all fluorescent
tubes require the use of mercury. Another benefit of LEDs is the solid-state
nature making the light emitting semiconductor very durable and with a long
lifetime of up to 100,000 hours. An epoxy resin is used for the LED enclosure
that allows the most amount of light to escape from the semiconductor, focuses
the light and protects the LED semiconductor from external elements making the
LED virtually indestructible. In comparison, fluorescent lighting generally is
limited to 50,000 hours while candescent lighting is significantly shorter and
both are easily susceptible to physical damage. LED-based lighting is expected
to supplant both incandescent and fluorescent lighting in the future.
There are generally two semiconductor materials that are used to manufacture
LEDs: gallium nitride (GaN) and indium gallium nitride (InGaN). GaN
transistors are used for its ability to work in hot temperatures and high
voltages. InGaN is a semiconductor material that is the result of a mixture of
GaN and indium nitride (InN). InGaN can also be used in high temperature
settings.
The white LED package can be manufactured using a single LED chip or multiple
LED chips. In a single LED chip package, there are two methods of generating
white light. White light can be generated by using a blue LED chip and
applying a yellow phosphor or by using a ultra-violet (UV) LED chip. For
multiple LED chip packages, two or three LED chips can be used to generate
white light. For instance, in a three LED chip package design, a red LED chip,
a green LED chip and a blue LED chip can be used to generate white light.
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