L11, Light Emitting Diode (LEDs)

LED's are the Light Emitting Diode, they are available in different types and with various color such as Red, Green, Blue, White, etc.

And the other good thing about them is they are easily available in any electrical shop nowadays at a cheap rate (they will cost you approximately 2 rupees per LED)

They work on DC source of 3 volts at there is maximum power. They have very long life and are very efficient.LED's mainly has two point for the connection i.e. Cathode and Anode

If you are confused about how to identify which one is cathode and which is anode, then don't worry i will be giving you some cool tips.

In the above figure you can see a single LED having two different sized legs. Yes! this is the trick, the shorter leg is the Cathode (-) and the longer leg is the Anode(+). Sometimes you may get a damaged or a used LED's, there it can be a difficult job to identify the cathode and anode. For that purposed here is an another trick i.e. you have to look into LED to identify cathode and the anode. Study the picture below carefully to understand LED.

While viewing into the LED you will see a smaller lead and the bigger lead. The smaller lead resembles the Anode and the bigger lead resembles the cathode. Sometimes while using color LED, it is difficult to see inside the LED, there is a flat surface at the base of the LED resembling Cathode. You can see that in the picture naming (cathode index flat).

And if you connect this LED to two 1.5 volt batteries it will glow as in the above figure. Resistor in connected in series with the LED in order to avoid high voltage from damaging the LED.

Value of the LED depend upon the brightness we need.

  • The color of the emitted light is decided by its wavelength.

  • As we know LED's are made up of semiconductor material, hence the "color of the LED epends upon the material used to made LED."

  • Silicon and Germanium are not used because they do not emit light in the visible spectrum.

· Colors associated with the different materials are as follows

· RED OR YELLOW --- Gallium Arsenide Phosphide (Ga As P) is used.

· RED OR GREEN --- Gallium Phosphide (Ga P) is used.

· Infrared --- Gallium Arsenide (Ga As) is used.

· Blue --- Gallium Nitride (Ga N) is used.

· Some LED's are capable of emitting infrared light which is not visible to our eyes.

· Supply voltage This is how much power you're putting into the circuit. Batteries and wall warts will have the output voltage printed on them somewhere. If you're using multiple batteries*, add the voltage together.

· LED Voltage Sometimes "Forward Voltage" but usually just abbreviated "V".

· LED Current Sometimes "Forward Current". This is listed in milliamps or "mA".

Both of these last two can be found on the packaging for your LEDs or on your supplier's web site. If they list a range ("20-30mA") pick a value in the middle (25 in this case). Here are some typical values, but use your own values to be sure you don't burn out your LEDs.

Operating voltage- Red LED: 2V 15mA Green LED: 2.1V 20mA Blue LED: 3.2V 25mA While LED: 3.2V 25mA

· Parallel connection of LEDs

How to find its Series Resistance? Watch video on YouTube


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