!GENERAL LED HANDLING PRECAUTIONS
  1. LEDS are static sensitive devices. Observe static sensitivity handling precautions, such as wearing a grounded wrist strap when handling.
  2. When forming leads, the leads should be bent at a point at least 3 mm from the base of the led
  3. Avoid damage to LEDS by soldering for no longer than 3 seconds with 700° iron
  4. The following information applies only to single LED components, not LED Bulbs and Products. All of our LED bulbs and products have resistors built-in for operation at their rated voltages. LED components are not considered bulbs, an LED bulb is a complete system consisting of LEDs, LED drivers or resistors, and a housing.
  5. ALWAYS USE A RESISTOR IN SERIES WITH THE LED OR LEDS. The forward voltage rating is TYPICAL and can vary from part to part, so while some LEDS may work fine just connected to a battery of the proper voltage, others will be overdriven and be destroyed. Here are a couple of useful links regarding this issue:
    Why do I need a resistor with an LED?
    LED Series/Parallel Wizard (for dealing with more than one LED per circuit)
    Purchase LED Resistors

LED calculator: current limiting resistor value

Supply voltage V [3-24 V]
Diode forward voltage V [2-4 V, or more for series combinations]
Diode rated current mA [10-50 mA, or more for parallel combinations]
Calculated resistance value Ohms
Next standard 5% resistor * Ohms
Resistor color markings
Power dissipated in LED** mW
Power dissipated in resistor** mW
* This calculator rounds the resistance up to the next standard resistor value. You should actually be able to buy a 5% resistor with the value returned by the calculator.
** Power calculations assume use of the standard value current-limiting resistor shown above.
LED calculator version 1.4 Copyright 2001-2004, Rob 'linear' Arnold. All rights reserved.
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LED INTENSITY

The unit of measure commonly used to describe LED intensity is the millicandela (mcd), 1000 millicandela equals 1 candela. Candelas measures how much light is produced as measured at the light source.
The candela is the Luminous Intensity, in a given direction, of a source of monochromatic radiation of frequency 540 × 1012 hertz and that has a radiant intensity in that direction of 1/683 watt per steradian.

The unit of measure commonly used for most other light sources is the Lumen.
Lumens are units of Luminous Flux and they measure how much light actually falls on a surface.
The Luminous Flux (lumens) from a light source is equal to the Luminous Intensity (candelas) multiplied by the solid angle over which the light is emitted, taking into account the varying intensities in different directions.
So you can see that it is not a simple matter to accurately convert millicandelas (mcd) to lumens but here is link to a handy program that will do it for you: Luminous Intensity to Lumen Converter

To use leds for 12 Volt applications you must simply connect a resistor in series with the led or leds. The resistor will drop the excess voltage and limit the current. See the Forward Voltage spec on the spec sheets (click the LED part numbers on the main LED page) for typical and maximum forward voltage, they're not all the same. Use a 1/8th watt or larger resistor soldered to the anode of the led and connect the +12 to the resistor. The chart below shows you the forward current for each color led with a single led in series with a 470 ohm resistor connected to 12 VDC. The current (and led brightness) will be slightly higher when the vehicle's engine is running because the battery charging system keeps the voltage up at around 13~14 volts. You can connect up to 4 red, orange, or yellow leds in series with each other and one resistor to power with 12 volts. The value of the current resistor must be lowered, depending on how many leds are in series. A maximum of 3 of the other colors can be in series across 12 volts, because of their higher forward voltage requirement.

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See our LED car bulb pages for LED bulbs designed to work on 12 Volt systems


LED COLOR RESISTOR - Ohms CURRENT @ 12 VDC
WHITE 470 18ma
BLUE 470 18ma
GREEN 470 18ma
AQUA 470 18ma
RED 470 20ma
YELLOW 470 20ma
ORANGE 470 21ma

TRY THESE LINKS FOR ADDITIONAL USEFUL LED INFORMATION

The Current State of Solid State Lighting - SSL
Circuitboards.com
Don's LED Pages
LED Center