I have mentioned that I think the LEDs are not getting 5v (probably closer to 4.5v, and that maybe the other reversed LED in the circuit is having some current limiting effect.
I thought so you don't have a clue about what is limiting the LED current.
Let me tell you then, although given your track record you will probably not understand this.
The peak current is limited by the source impedance of the arduino output pins. This in effect is your resistor. The bad bit about this is that from my experiments I have found that you can get about 240mA from a single arduino pin. See this, these are real measurements and they surprised me as well.
http://www.thebox.myzen.co.uk/Tutorial/LEDs.html
So that is more than the limit for a whole 328 chip going through one pin. I have pointed you at this web site before.
Oh an while we are on the topic of you not understanding things having read my decoupling tutorial:-
http://www.thebox.myzen.co.uk/Tutorial/De-coupling.html
You come to the conclusion
Hippynerd:
I looked over mikes decoupling page, and things are still rather complicated and hard to understand everything, but its good to have that as a reference. As I understand it, if the caps arent quite right, there can be a lot of RF noise, and I guess its common for folks to just throw some caps at it, and be unaware of the noise issue. I dont like solving problems by making other problems, which is what im trying to avoid, while learning...
How on earth any one can come to the conclusion that using caps that are not quite right will GENERATE RF noise. That is a totally wrong conclusion and further underlines your credentials for giving advice to anyone about anything electronic.