ROBOT.LK

I found a nice site that you can use to calculate resistor values automatically in LED arrays. The wizard suggests the number of LEDs which can connect in series and number of such sets in parallel. Here is an example out put for following values.

Source voltage: 12
diode forward voltage: 2*
diode forward current (mA): 20*
number of LEDs in your array: 100
*See 5mm LED typical technical data

Option 1:

• each 1 ohm resistor dissipates 0.4 mW
• the 220 ohm resistor dissipates 88 mW
• together, all resistors dissipate 94.4 mW
• together, the diodes dissipate 4000 mW
• total power dissipated by the array is 4094.4 mW
• the array draws current of 340 mA from the source

Option 2:

• each 100 ohm resistor dissipates 40 mW
• together, all resistors dissipate 800 mW
• together, the diodes dissipate 4000 mW
• total power dissipated by the array is 4800 mW
• the array draws current of 400 mA from the source

Have a look: http://led.linear1.org/led.wiz