Light Emitting Diodes (L.E.D.'s)

 

Alert

Tuned In

Turned On

Light

Time Up

On Standby

Display

In Progress

Select

Ready

L.E.D's are available in many coloured shapes and sizes. They are mainly used as indicators to tell you if something has turned on or happened.

They even light up traffic lights.

They can be
used to tell

you that your
food is
cooking in
the
microwave
or your TV
or computer
is on
standby.

They are often used
to display numbers
in clocks. Did you
know that James
Bond's first digital
watch used L.E.D.
technology?

 

They can
inform you
that a device is
switched on
and working.

 

Over the past twenty years the original technology has been
developed much further to produce flat panel screens. These
are now commonly used as computer monitors and wide
screen TV's in many of our homes. The L.E.D. is a very
popular component and seen in many of the products that
we buy.

The L.E.D. Closeup.

When a small current flows through an L.E.D. (normally
about 20-30 milliamps) it will light up. Unlike an ordinary bulb,
its two connections ( + and -) must be connected correctly to
the power source for it to work.

Standard L.E.D.
Symbol

 

 

The two different connections to the L.E.D. are :

1, The Anode (+)

2, The Cathode (-).

These can be identified by looking for either the long (+) or
short (-) legs. The flattened edge of the led is always nearest
to the Cathode (-). Please look carefully at the image above
to see this.

Q21, The long leg of an L.E.D. is called the .


 

Q22, Click on the L.E.D. symbol below which has
been drawn correctly.

 

 

 

 

 

 

Q23, L.E.D. wrist watches are rarely seen these days. Which of these explains why?:

They run batteries down too quickly
They give off dangerous rays
They can't be seen in the dark
They weigh too much

 

Q24, The current used by an LED is typically about
20 - 30 milliamps.This is the same as:

20 - 30 thousandths of an amp
20 - 30 thousand amps
20 - 30 million amps

Getting it working

L.E.D.'s are semiconductors and most of them cannot work
safely in a circuit on their own. This is because they allow too
much current to flow. By comparison, light bulbs take just the
amount of current they need.

To protect the L.E.D., it is necessary to use an electronic
component called a resistor. This is connected in series with it.

Please go on to the next section now to find out about this.

Page 6