在PI中从浏览器执行GPIO python

Im trying to execute a php script that invokes a python program to control GPIO pins in Raspberry Pi. i'm able to get it work by running it in the terminal. But when i run it from midori browser im not able to get it work...pls help me out the below is the php code...!

<?php
    echo "Executing Python";
    exec("python /usr/bin/Light.py");
 ?> 

the following is the python code

import RPi.GPIO as GPIO
 import time

 def blink(pin):

GPIO.output(pin,True)

   time.sleep(1)

GPIO.output(pin,False)

time.sleep(1)

return

GPIO.setup(11,GPIO.OUT)

for i in range(0,20):

  blink(11)

 cleanup()

Thanks in advance !

Add permission for www-data: sudo visudo

Add the following line to the end: www-data ALL=NOPASSWORD: /usr/bin/Light.py

Unless you've changed the permissions, you need to run as root to use the GPIO module