LED Emitters and Kits

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Light emitting diodes (LED's) are electronic components that produce light without heat or high voltages. When using LED's in a DC circuit there are some basic rules you will need to follow. LED's must be operated in such a way that the current through the LED is kept within the limitations of the device. The simplest is to place a current limiting resistor in series with the LED. The resistor value can be calculated using Ohm's law. Each LED type has specification called "forward voltage drop", they also have a specified current limit. Both these specifications are required in order to calculate the size of the resistor required to limit the current.
The following is a general guideline for LED's without specifications.

Forward Voltage Drop: Regular red 2.0v High brightness red 2.2v Super bright red 3.0v Orange or yellow 2.0v Regular green 2.0v High Brightness green 2.2v Super bright green 3.3v Blue 3.4-4v White 3.4-4v Forward Current 20mA is a common standard value for most LED's. Anode & Cathode Most Led's have a long lead and a short lead, the longer lead is the anode ( positive ) and the shorter lead is the cathode ( negative )	Calculating the Value of the Current Limiting Resistor Using a standard green LED with 2.0 Volt forward voltage drop and a forward current of 20mA and we want it to run in a 12 Volt DC circuit. ( 20mA = .02 Amps ) Using Ohm's law: Subtract the forward voltage drop from the supply voltage. 12 Volts - 2 Volts = 10 Volts Then: 10 Volts Divided By .02 Amps = 500 ohms As resistors come in standard values, choose the next highest value, this will reduce the current slightly. To calculate the wattage rating of the required resistor: W=A x V .02 x 10=.2 watts Therefore use a 1/4 watt resistor	Connecting Multiple LED's in Series Series LED's are connected cathode to anode to cathode to anode. The limiting resistor is placed between the voltage source and one of the LED leads. In this type of circuit you need enough voltage to power the number of LED's you are using. To calculate the required resistor: Add the forward voltage drop for each LED together and subtract the total from the supply voltage. For example if you have 4 LED's each with a 2 Volt voltage drop and a supply voltage of 12 Volts DC: 4 x 2.0V=8.0V 12V-8.0V=4.0V 4.0V will be the voltage at the resistor. Then: 4.0V divided by .02A=200 Ohms use the next highest standard resistor value For the resistor wattage: .02A x 4.0V=.80W ( 1/4 watt resistor ). With a series LED circuit you can use any combination of LED colors with different voltage drops.	Multiple LED's in Parallel LED's in parallel is not a good idea. The LED's will not have exactly the same voltage drop and because of these differences they will have different brightness levels and may be destroyed by the larger current flowing through it.
5mm Ultra-Violet Emitter Ultra-Violet used in money watermark detectors, blood and stain detectors #324 20 Pak / $8.50 Includes Free Shipping	5mm IR LED Emitter IR illumination for night vision equipment and applications Input voltage: 1.7Volts - 2.2 Volts #145 20 Pak / $8.50 Includes Free Shipping	10.5mm LED Emitter Focused light output Resistor needed at 4.5 volts #552 9 Pak / $7.75 Includes Free Shipping	12000 mcd LED 5mm White Emitter View Angle 15 Degrees #136 10 Pak / $9.30 Includes Free Shipping
1000 - 1500 mcd LED 5mm Yellow Emitter Input voltage:1.9V-2.0V #744 10 Pak / $6.70 Includes Free Shipping	8000 + mcd LED 5mm Green Emitter (515~520nm wave) Input voltage: 3.2V~3.4V #743 10 Pak / $6.90 Includes Free Shipping	1500-2000 mcd LED 5mm Blue Emitter #144 10 Pak / $6.80 Includes Free Shipping	Bulk LED Emitters One big mess of prime new LEDs. No specifications are available. 100 pieces of LED emitters, some in plastic housing, and some IR Emitters. Apply 1 volt dc and step up till you get a glow from the lamp to find the forward voltage. #521 100 Pak / $12.00 Includes Free Shipping
8 Volts 250 ma Type A Lamp #82 3 Pak / $8.95 Includes Free Shipping LED Emitter Tester #716 $9.46	Assembled mini traffic light kit. It has 3 LEDs: one green, one red and one yellow. After connecting the power, it takes a few seconds before the LEDs start flashing sequentially, one after the other. It is possible to connect up to 12 LEDs to the circuit using 4 of each colour. The additional LEDs are not included. Specifications: Supply Voltage: 4.5 - 6Vdc Supply Current (using 3 LEDs): 350mA at 6V Dimensions: 35 x 45mm, 25mm height #10008 $12.82 Includes Free Shipping	"Blinder" LED Flasher Kit Kit features 3 crystal clear special LEDs which create brilliant flashes of orange-red light. The light output of this flasher kit can be seen in direct sunlight. Great for night joggers, bicyclists, warning markers, etc. Size of PC board: 2" x 1.4". Operates on one 9V battery (not included). Flash rate is adjustable with the built-in trimmer potentiometer. Complete with all parts, PC board and instructions. Skill Level 1. This kit requires soldering of components to the PC board while building. #820 $11.96 Includes Free Shipping