I am trying to implement one of the starter circuits using your library. This simple Arduino code, causes the LED to light up brightly and blink accordingly (everything seems correct):

void loop() {  
  digitalWrite(13, HIGH);
  delay(1000);
  digitalWrite(13, LOW);  
  delay(1000);              
}

But this Python code, causes the LED to blink correctly, but is very dim with the exact same circuit:

from Arduino import Arduino
import time

board = Arduino('9600') #plugged in via USB, serial com at rate 9600
board.pinMode(13, "OUTPUT")

while True:
    board.digitalWrite(13, "LOW")
    time.sleep(1)
    board.digitalWrite(13, "HIGH")
    time.sleep(1)

Any ideas what could cause this?