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12v led taillights

  1. Mar 16, 2009 #1
    I work on cars, and love the led look in the taillgiht of a car or vehicle. I want to learn how to make them, I know how to solder. I have made one just playing around, but am not sure if it is set up right. The first questiong I have is how do figure what type of resistor to use with how many leds to get the max light out of the leds without burning them out? Thanks for you time.
  2. jcsd
  3. Mar 21, 2009 #2
    You need to know the maximum current spec of the LED you wish to use. Considering it's for a car, you will most likely use 12vdc. Once you find the rated current, you can find the resistance using the following equation: V = IR where V is voltage, I is current (in amps) and R is resistance (in ohms).
  4. Mar 21, 2009 #3
    Thanks for your time...

    Size: 5mm

    Lens Color : Water Clear

    Forward Voltage (V) : 2.0~2.4

    Forward Current (mA):20

    View Angle: About 25 degree.
    Static Sense:Yes

    Luminous Intensity: 15000mcd
    Life Rating : 100,000 Hours
  5. Mar 21, 2009 #4
    LED Taillights use Pulse Width Modulation (PWM) to change brightness for taillight to brake.

    There are a few solder together PWM demonstration kits to get started.
  6. Mar 22, 2009 #5


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    riviknights, if you want a simple circuit to get you started then try using 4 of those LED's (in series with each other) in series with one 270 ohm resistor. That is all five componets in one series circuit. That will get you somewhere near maximum brightness reasonably safely.
  7. Mar 22, 2009 #6
  8. Mar 22, 2009 #7
    Thanks for all the help and advice, I greatly appeaciate it. I'm going to make some trial and test lights, I think I have enough information now, but just one more ? What is the lowest amount of power that can be put to these leds? I mean is there a minimum? Thanks agian for all the help. I will be back to show my result once I get them done.
  9. Mar 23, 2009 #8


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    The minimum power is zero.

    If you want a low power setting then try about 5mA (which will reduce the voltage on each LED to about 1.7 volts) giving about 8 to 10 mW per LED
  10. Mar 23, 2009 #9
    This page on my site shows a PWM circuit used to save battery power with LED lights.
    It was found that the human eye could not detect the difference if duty cycle was 1:3.
    Link here:-
    Last edited by a moderator: Apr 24, 2017
  11. Feb 6, 2010 #10
    hi, I have made a circuit connected to an led . It produces very low voltage,which could not be measured by multimeter.so ,if any one have better idea to measure that ,please reply.
    And I also want to know about the minimum power ,voltage and current required for lighting the LED.thanks
  12. Feb 7, 2010 #11
    Is the LED lit when you measure this very low Voltage?
    I assume not. So
    1. your driver circuit is not working. or
    2. your LED is faulty and causing a short circuit.

    A standard red LED will need about 2Volts and will draw about 10mA for normal brightness.
    Power = VI =2X0.01 = 0.02Watts = 2mW.
    Hope this helps.
    Last edited by a moderator: Nov 7, 2011
  13. Feb 9, 2010 #12
    SIR, the LED lit (that's what the main problem is)with a very low brightness.I have tested the LED in other circuit and it doesn't have any fault,so the problem still remain as it was.
    Last edited by a moderator: Nov 7, 2011
  14. Feb 9, 2010 #13
    It sounds as if your driver circuit has a very high resistance, which would cause a large volt drop when a current is taken from it.
    It would help to know what that circuit is.
    Last edited by a moderator: Nov 7, 2011
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