An LED is often small in area (less than 1 mm2), and
integrated optical components may be used to shape its radiation pattern.
Appearing as practical electronic components in 1962, the
earliest LEDs emitted low-intensity infrared light. Infrared LEDs are still frequently
used as transmitting elements in remote-control circuits, such as those in
remote controls for a wide variety of consumer electronics. The first
visible-light LEDs were also of low intensity, and limited to red. Modern LEDs
are available across the visible, ultraviolet, and infrared wavelengths, with
very high brightness.
Early LEDs were often used as indicator lamps for electronic
devices, replacing small incandescent bulbs. They were soon packaged into
numeric readouts in the form of seven-segment displays, and were commonly seen
in digital clocks.
Recent developments in LEDs permit them to be used in
environmental and task lighting.
LEDs have many advantages over incandescent light sources
including –
- Lower energy consumption,
- Longer lifetime,
- Improved physical
robustness,
- Smaller size, and
- Faster switching
Light-emitting diodes
(led’s) are now used in applications as
diverse as aviation lighting, automotive headlamps, advertising, general
lighting, traffic signals, and camera flashes. However, LEDs powerful enough
for room lighting are still relatively expensive, and require more precise
current and heat management than compact fluorescent lamp sources of comparable
output.
LEDs have allowed new text, video displays, and sensors to be
developed, while their high switching rates are also useful in advanced
communications technology.
Flashing led
Most flashing LEDs emit light of one colour, but more
sophisticated devices can flash between multiple colours and even fade through
a colour sequence using RGB colour mixing.
Bi-colour LED
Two different LED emitters in one case.
A decorative garden light that changes colour.
Tri-colour led
Three different LED emitters in one case. Each emitter is
connected to a separate lead so they can be controlled independently.
RGB led
Tri-colour LEDs with red, green, and blue emitters, in
general using a four-wire connection with one common lead.
Decorative multicolour led
Incorporate several emitters of different colours supplied by
only two lead-out wires. Colours are switched internally simply by varying the
supply voltage.
Alphanumeric led
Available in seven-segment, starburst and dot-matrix format.
Seven-segment displays handle all numbers and a limited set of letters.
Starburst displays can display all letters. Dot-matrix displays typically use
5x7 pixels per character.
Digital RGB led
These
are RGB LEDs that contain their own "smart" control electronics. These
are connected in a daisy chain, with the data in of the first LED sourced by a
microprocessor, which can control the brightness and colour of each LED
independently of the others. They are used in strings for Christmas and similar
decorations.