Transcript What is an LED? - Advanced Control Technologies, Inc.

What is an LED?
LED stands for Light Emitting Diode
This is how they work…
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How Diodes work
A diode allows an electric current to
flow in one direction, but blocks it in the
opposite direction, much like an
electronic version of a check valve.
How Light Emitting Diodes
work
A Light Emitting Diode emits light when
an electric current passes through it.
Basically, LED's are tiny light sources
that fit easily into an electrical circuit.
Why get light from LEDs?
They are illuminated solely by the
movement of electrons in a very
small piece of semiconductor material
inside them referred to in the “LED
world” as a die.
They don't have a filament to burn
out, and they don't get especially hot.
How are LEDs made?
These dies, the main
component in LEDs, are
processed in wafer form
similar to silicon-integrated
circuits, and broken out into
individual dice or chips.
Chip size for visible signal LEDs generally fall in the
range of 0.18mm square to 0.36mm square (smaller
than a pin head). High power LEDs for lighting are
yet larger.
Internals of a Blue LED
White visible light starts with
a die that emits blue light (It’s
coated with Indium gallium
nitride, causing the blue
coloring)
The basic LED structure
consists of the die, a lead
frame where the die is
actually placed, and the
encapsulation epoxy, which
surrounds and protects the
die and disperses the light
(see left).
What about a White LED?
To create White light, a
coating of phosphor is
placed on the die.
The recess in the anvil is
shaped to project the
radiated light forward.
The die's top contact is wire
bonded to the other lead
frame terminal, the post, to
complete the circuit.
So, how do you get white
light?
As current flows, the die would normally produce
blue light. But in this case another color is
emitted as determined by the precise amount of
phosphor applied to the die. That phosphor
fluoresces to achieve a near-white light
That white light is sorted to colors like warm
white, white and cool white and assembled in
quantities in tubes.
These LEDs are mounted on printed
circuit boards in shatter-resistant
Polycarbonate tubes…
…with proper
electrical
contacts they
are designed
to replace
fluorescent
lamps!
How long do LEDs last?
LEDs have a mean time between failures usually
in the range of 100,000 to over 1,000,000 hours.
But, this is a long time for continuous operation,
considering that a year is 8784 hours at most. *
Temper this with application, added circuitry and
housing. In practice, the useful measure of LED
lifetime is its half-life. When the light output
falls off to half the original, an LED is deemed to
have reached the end of its life
* Based on life decay model, 67-21 series lifetime can reach L70@ 25297 hr and L50@ 47466 hr under test condition of
20mA, 25 C and 60%RH.
How do fluorescent tubes work?
 Electricity flowing from
electrode to electrode in
fluorescent lamps produce
a charge causing
electrons to travel through
the argon gas-filled tube.
This energy vaporizes
liquid mercury inside the
tube which in turn
releases ultraviolet (UV)
photons.
The ultraviolet light is transformed into visible light by the
phosphors on the inside of the tube. In doing so, about 80%
of the energy used is released as heat not light and, in a
warm climate, that increases your air conditioning costs.
Lamp lifetimes compared
Hours x 1000
50
45
40
35
30
25
T12
T8
20
15
10
5
0
LED
Life
Expectancy
Some facts about fluorescent tubes





Require inefficient, expensive ballasts
Generate higher utility bills
Significantly shorter life than LEDs
Poor performance in cold environments
Require immediate replacement, or
have wasted life from group relamping
 When broken, you have glass shards
contaminated with mercury
 Can sound noisy and flicker as they age
 Dimming is too expensive to be practical
Benefits of LED Lites
Long life (50,000 hrs).
60% savings in your
lighting energy bill.
No humming/no buzzing.
Do not generate significant heat.
Not affected by vibration.
No toxic components, no disposal costs.
Do not attract insects.
Efficient in cold temperatures.
What savings can I expect?
 A building operating 12 hours a day can usually pay
back the cost of the lamps in electrical savings within 24
months. The balance of the life of the lamps (7-8 years)
can show savings of 60% or more over previous
expenditures. Dollar amounts are dependent on the
number of fixtures and local power rates.
 A savings calculator is available. Merely plug in figures
found in a lighting survey of your building.
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How about even more
savings?
Dimming LED Lites (controlLED Lites) provide
even more savings.
controlLED Lites can operate from a variety of
control signals.
They can controlled by occupancy or light
level sensors and be connected to existing
building automation systems.
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