Hi all, can someone tell me if I was to run LED's off 9 volts what size resistor would I need to use.

Best regards Dave.

I put together a dome light in my truck(40ultra bright super flux leds). I just made my circuit and used two 1watt 100ohm resistors..Its not the proper way to do it , but it can be done.

so it is possible to use 1 resistor light up the whole works.. I would stress that you bread board that circuit first ,more so if your leds are not all the same. its is possible to blow leds doing what I did.

Chances are , 3.2v and 20ma are general led power requirements ,On 9 volt

http://led.linear1.org/led.wizSolution 0: 2 x 4 array, 1 extra LED

+----|>|----|>|---/\/\/----+ R = 150 ohms

+----|>|----|>|---/\/\/----+ R = 150 ohms

+----|>|----|>|---/\/\/----+ R = 150 ohms

+----|>|----|>|---/\/\/----+ R = 150 ohms

+----|>|----------/\/\/----+ R = 330 ohms

The wizard says: In solution 0:

each 150 ohm resistor dissipates 60 mW

the wizard says the color code for 150 is brown green brown

the wizard thinks ¼W resistors are fine for your application

the 330 ohm resistor dissipates 132 mW

the wizard says the color code for 330 is orange orange brown

the wizard thinks ¼W resistors are fine for your application

together, all resistors dissipate 372 mW

together, the diodes dissipate 576 mW

total power dissipated by the array is 948 mW

the array draws current of 100 mA from the source.

Solution 1: 1 x 9 array uses 9 LEDs exactly

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

+----|>|---/\/\/----+ R = 330 ohms

The wizard says: In solution 1:

each 330 ohm resistor dissipates 132 mW

the wizard says the color code for 330 is orange orange brown

the wizard thinks ¼W resistors are fine for your application

together, all resistors dissipate 1188 mW

together, the diodes dissipate 576 mW

total power dissipated by the array is 1764 mW

the array draws current of 180 mA from the source.