led powerpoint new

8/2/2019 Led Powerpoint New

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By:

Gonzales, Frankie C.Legaspi, Jorrel Angelo S.

Lopez, Allan Paul

Lozares, Patrick


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Figure 4.1 Light Emitting Diode Anatomy


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INVENTION AND DEVELOPMENT

In 1906, Henry Joseph Round first reportedelectroluminescence while experimenting with Silicon

Carbide (SiC). In 1955, Rubin Braunstein (born 1922) of

the Radio Corporation of America first reported on

infrared emission from Gallium Arsenide (GaAs) and other

semiconductor alloys. In 1962, Nick Holonyak Jr. (born

1928)

General Electric Company invented the first practical

light-emitting diode operating in the red portion of thevisible spectrum. Throughout the later 1960s and 1970s,

further invention and development produced additional

colors and enabled LEDs to become a readily available

commercial product.


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How LEDS Work?

When certain elements are combined in specific configurations and

electrical current is passed through them, photons (light) and heat

are produced.

When a sufficient voltage is applied to the chip across the leads of

the LED and the current starts to flow, electrons in the n region

have sufficient energy to move across the junction into the p region.

Once in the p region the electrons are immediately

attracted to the positive charges due to the mutual Coulomb

forces of attraction between opposite electric charges.

When the electron and holes recombine, photons (light)

are created.


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COLOR

The color-emitted light of LEDs depends on the chemicalcomposition and dominant wavelength of the semiconducting

material used.

Tri-color LEDs

The most popular type of tri-color LED has a red and a green

LED combined in one package with three leads. They are called

tri-color because mixed red and green light appears to beyellow and this is produced when both the red and green LEDs

are on.


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Bi-color LEDs

A bi-color LED has two LEDs wired in

inverse parallel (one forwards, one

backwards) combined in one package with

two leads. Only one of the LEDs can be lit atone time and they are less useful than the tri-

color LEDs described above.


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TECHNICHAL DATA FOR LEDs

Type ColourIF

max.

VF

typ.

VF

max.

VR

max.

Luminous

intensity

Viewing

angleWavelength

Standard Red 30mA 1.7V 2.1V 5V 5mcd @ 10mA 60 660nm

Standard Bright red 30mA 2.0V 2.5V 5V80mcd @

10mA60 625nm

Standard Yellow 30mA 2.1V 2.5V 5V32mcd @

10mA60 590nm

Standard Green 25mA 2.2V 2.5V 5V32mcd @

10mA60 565nm

High intensity Blue 30mA 4.5V 5.5V 5V60mcd @

20mA50 430nm

Super bright Red 30mA 1.85V 2.5V 5V500mcd @

20mA60 660nm

Low current Red 30mA 1.7V 2.0V 5V 5mcd @ 2mA 60 625nm


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SIZES, SHAPES AND VIEWING ANGLES

LEDs are available in a wide variety of sizes and shapes. LED die sizes range

from tenths of millimeters for small-signal devices to greater than a squaremillimeter for the power packages available today The standard LED has a

round cross-section of 5 mm diameter bullet shape and this is probably the

best type for general use, but 3 mm round LEDs are also popular.

Round cross-section LEDs are frequently used and they are very easy toinstall on boxes by drilling a hole of the LED diameter, adding a spot of

glue will help to hold the LED if necessary. LED clips are also available to

secure LEDs in holes.


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LUMEN DEPRECIATION

Lumen depreciation is the lighting attribute most oftenused to determine the useful life (minimum maintained

illuminance level) of LED sources. LEDs do not fail abruptly;

instead, they dim with time. Although a 50,000 to 100,000-

hour life is commonly attributed for LED. The best LED

achieved 70 percent of original light output at 50,000 hoursof operation under standard use conditions.

One of the key limitations affecting LEDs is temperature. A

common maximum junction temperature rating is more than130oC. The higher the design junction temperature, the

faster the light output will degrade.


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ADVANTAGES OF USING LEDs

LEDs are capable of emitting light of an intended color without

the use of color filters that traditional lighting methods require.

The shape of the LED package allows light to be focused.

Incandescent and fluorescent sources often require an external

reflector to collect light and direct it in a useable manner.

LEDs are insensitive to vibration and shocks, and they are

solid-state devices that do not use gases or filaments. Thusextremely high reliability against mechanical shocks and

vibrations are achieved.


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LEDs are built inside solid cases that protect them, makingthem hard to break and extremely durable and moisture-

tolerant. However, the electronic circuitry (drive

circuitry/power) that surrounds them in a system is not.

Since LEDs are low-voltage devices, LED systems are safer

than other lamp systems that require high voltages. In

addition, visible-wavelength LEDs do not generate

appreciable amounts of ultra-violet or infrared.

LEDs have an extremely long operating hours, twice as

long as the fluorescent lamps and fifty times longer than the

incandescent bulbs.



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Further, LEDs fail by dimming over time, compared with the

abrupt burn-out of incandescent bulbs. LEDs give off less heat

than incandescent light bulbs with similar light output.

LED lights up very quickly and will achieve full brightness inapproximately 0.01 seconds, 10 times faster than an

incandescent light bulb (0.1 second), and many times faster

than a compact fluorescent lamp, which starts to come on

after 0.5 seconds or 1 second, but does not achieve fullbrightness for 30 seconds or more.


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DISADVANTAGES OF USING LEDs

LEDs are currently more expensive than more conventionallighting technologies. The additional expense partially stems

from the relatively low lumen output (requiring more light

sources) and drive circuitry/power supplies needed.

LED performance largely depends on both current density and

junction temperature. More light output degradation occurs

whenever either of these parameters is increased. It is very

important that the specified LED junction temperature not be

exceeded for effective LED system operation. Adequate heatsink is required to maintain long life.


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LED APPLICATIONS

While LEDs may be more expensive than incandescent

lights up front, because theyre built around advanced

semiconductor material, their lower cost in the long run

can make them a better buy.

The main drivers for conversion to LEDs are higher

efficiency, long life, reduced maintenance, and increased

and superior visibility, making LEDs a more cost-effective

lighting option for a wide range of situations. Below areexamples of different usage of LEDs.


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(a) seven segment in showing numbers in

calculators and measurement

instruments.

(b) in dot matrix arrangements fordisplaying messages displays in public

information signs (banks, hotels, airports

and railway stations and as destination

displays for trains, buses, and ferries).

(c) remote controls for TVs, VCRs, etc.,using infrared LEDs.

(d) traffic signals

(e) pedestrian signs

(f) highway sign panels

(g) railroad signals

(h) marine navigational lights

(i) emergency beacon or strobe lights at

airports

(j) exit signs


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Seven-segment LED

Dot matrix LED


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Exit and Emergency Sign Backlight LED


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LED SHOWER LIGHT

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