Now i get it! resistors...

I have always seen people using 100 ohm resistor to a simple led, but I have never understand why. I have use led many times without resistor and no problem.

but yesterday i got it!
From this:

To this:

YES. it's on!











My lab board are connected to a PC and webcam, so I and a friend far away still can do some grate experiments. On it right now: Arduino mega, 433mz transmitter and receiver, 5 leds(without resistors....) and LCD screen.