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DW: LED

Page history last edited by Joel Rosenberg 11 years, 8 months ago

LED (Light Emitting Diode)

Part of Diode group

Part of Circuit Outputs group

Part of Lighting group

 

What it Does

 

LEDs emit light when current flows from the positive (+) leg to the negative (-) leg. If connected backwards, they will not light. In this way, they are like a one-way valve, allowing current to flow in one direction but not the other.

 

LEDs come in many different colors and brightnesses, and can be used for such things as an indicator (e.g. circuit is powered on or off), as decoration, or as a light source (e.g. LED flashlight).


What it Looks Like / Schematic Symbol

 

diagram of LED 

 

 

      

Side View         Top view        Schematic symbol

 

 

 

How to Use

 

There are two ways to identify the (+) end of an LED:

     1) the bulb often has a flat side that corresponds to the (-) lead (and matches the line in the schematic symbol), so the other end is the (+) lead;

     2) the longer lead is the (+) lead, the shorter one is the (-) lead.

 

Protection resistor: LEDs require a resistor connected in series to limit the current through it (sometimes called a "current-limiting resistor"). The optimal resistor value can be calculated for a given LED, but usually a value between 100Ω and 1kΩ will work.

 

 

SCHEMATIC DIAGRAM 

 

The current through most common LEDs is around 20mA (0.020A).

 

The voltage needed to drive an LED depends on the color it produces.

Here is a table of common voltages.

 

Connection to the electromagnetic spectrum: Higher energy colors require a higher voltage to be produced.

  

 

Tips

 

Soft Circuits: Bend the (+) lead into a round spiral, and bend the (-) lead into a square spiral. Or use a permanent marker to color the (+) end red and the (-) end black.

bending LED leads

 

References

LED Datasheet: http://www.digitaldandt.org/db/index.php/datasheet/show/18

TEP Data Sheets: http://www.tep.org.uk/PDF/Electronics%20V1.2/data%20sheets.pdf

Duncan, Tom. Basic Skills Electronics. London: John Murray Ltd., 1988.

Duncan, Tom. Electronics for Today and Tomorrow. London: John Murray Ltd., 1985.

http://kaytdek.trevorshp.com/projects/conductive/tutorial/tutorial.html

 

Images

http://ledcalculator.net/

 

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