|
In general, you can use the following formula to work out what resistor you need for your LED.
R = (V - Vf) / I
Where:
V = supply voltage (ie 12V)
Vf = forward voltage of the LED (usually 1.5V to 2V for a red LED)
I = desired current through the LED.
For your 12V @ 10mA you'd end up with:
R = (12 - 1.5) / 0.01
R = 10.5 / 0.01
R = 1050 ohms (1K rounded down or 1K2 rounded up)
What you'll find is that Steve is quite correct, and you might even find that 10mA is too much depending on where you are placing the LEDs and their direction (right into your eyes for example).
What you can do is invest in a 5Kohm potentiometer and wire that up with your LED then at night adjust the pot until you get an acceptable brightness. Measure the resistance across the pot and find the nearest standard value resistor....
...or along with the 1.2K (1K2) resistor grab a 1K5 and a 1K8 as well and try those as well.
|