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LEDs are cool because they're tiny and long lasting (up to 10 years). Unlike incandescent bulbs, LEDs don't get hot. They also don't consume a lot of power.
LEDs come in many colors, brightnesses, sizes and shapes.
LEDs are polarized. The positive side (the side connected with the + side of the battery) is the longer leg and is referred to as the anode. The shorter leg, the negative side, is called the cathode. You won't hurt the LED if you accidentally plug it in backwards. It just won't work.
The color of an LED is determined by the semiconductor material and not by the package (plastic body). Different colored LEDs require different amounts of voltage to light up. Red, green, and yellow LEDs typically require 2.2V-2.4V. Super-bright white and blue LEDs can require up to 3.4V.The optimum voltage is referred to as forward voltage (VF).
Most LEDs require 20mAh of current flowing from the battery. Most batteries supply more than 20mAh, so you need to use a resistor to limit the flow of current to each LED so it won't burn out.
VF Forward Voltage is also referred to as Voltage Drop. It is the minimum amount of voltage needed to light up an LED.
lV Luminous Intensity is the amount of light emitted from an LED in a particular direction. It is measured in millicandela (mcd). You can consider this property as brightess. The greater the millicandelas the brighter the LED.
IF Forward Current is the amount of current the LED uses.
Viewing Angle is the spatial distribution or spread of light. It is expressed in degrees that measure the width of the light beam. LEDs with a small viewing angle produce a more focused beam, and LEDs with larger viewing angles produce a softer more dispersed beam.
| Type | Color | IF | VF Typ | VF Max | Luminous Intensity | Viewing Angle | Wavelength |
|---|---|---|---|---|---|---|---|
| Standard | Red | 30mA | 1.7V | 2.1V | 5mcd@10mA | 60° | 660nm |
| Standard | Yellow | 30mA | 2.1V | 2.5V | 32mcd@20mA | 60° | 565nm |
| Super bright | Red | 30mA | 1.85V | 2.5V | 500mcd@20mA | 60° | 660nm |
UV LED's emit a light that you don't see, but that can damage your eyes. Be careful!
To use a resistor calculator you need the following information:
- Supply voltage, the voltage from your power source
- LED voltage Drop
- LED Forward Current
- Number of LEDs you want to connect
- Connection— whether the LEDs are connected in series or in parallel
There are 3 ways to connect LEDs together:
- In parallel—each positive lead is connected to the positive lead of the next LED, and each negative lead is conected to the negative lead of the following LED.
- In series—each positive lead of an LED is connected to the negative lead of the next LED.
- Separate LED chains—chains of LEDs wired together in parallel can be combined all together in series
The decision to wire LEDs in series versus in parallel depends mainly on the following factors:
- the power source
- the number of LEDs
- whether you are using different colored LEDs together
Electricity takes the path of least resistance If you have two different colored LEDs, one red with a forward voltage of 2.2V and the other green with a forward voltage of 2.4V, the current will flow through and light only the red LED. The green LED will be circumvented. It is possible to mix colored LEDs with the same specifications in a parallel circuit, but often some of the LEDs end up appearing dimmer than the others.
When LEDs are connected in parallel, the voltage across each LED remains the same, and the current is divided between them.
A circuit with a 3V battery and a resistor will light up 2 red LEDs with forward voltages of 2.2V when wired in parallel. Each LED will receive its 2V and the current will be dispersed between the two LEDs—therefore, you'll drain your battery more quickly than if you had wired them in series.
When resistors are connected so that the same voltage is applied across each resistor, the resistors are said to be connected in parallel. The single equivalent resistance R of three parallel resistors can be determined from:
1/Rtotal=1/R1+1/R2+1/R3
A connection of two resistors in parallel is called a current divider
1/Rtotal=1/R1+1/R2+1/R3
A connection of two resistors in parallel is called a current divider
In series— When LEDs are connected in series, the voltage is divided equally across each LED, and the current remains the same. If you had a series circuit with a 3V battery, a resistor and 2 red LEDs with forward voltages of 2.2V, neither would light up as each would receive only 1.5V.
When resistors are connected in a circuit so that the same current flows through each resistor, the resistors are said to be connected in series. It is possible to determine the resistance of a single resistor that has the same resistance as a number of resistors in series. This single equivalent resistance is just the sum of the individual resistances. For three resistors in series, the equivalent resistance R is given by:
Rtotal = R1 + R2 + R3
A series connection of two resistors is called a voltage divider
Rtotal = R1 + R2 + R3
A series connection of two resistors is called a voltage divider
Connecting different colored LEDs
The power supply must be equal to or more than the sum of the voltage requirements for each LED and its resistor. If you want to mix colors and wire your LEDs in parallel, then you need to add the right resistor to each LED (not one for the entire circuit). This levels the amount of power required to illuminate each LED.
If your project requires the use of multiple LEDS and a small power supply, parallel wiring is the way to go.
Flashing LED
These LEDs contain an integrated circuit. They do not require resistors.IR LED
These LEDs emit Infrared light that is invisible to the human eyeThese are found in remote control devices
Piranha or High-Flux LED
These LEDs are square and have four leads: two are positive and two are negative.To distinguish the cathodes from the anodes you must refer to the LEDs' datasheet or create a simple ccircuit with alligator clips, a battery and a resistor.