light_sensor.py

#!/usr/bin/env python
     
import RPi.GPIO as GPIO, time, os
     
DEBUG = 1
GPIO.setmode(GPIO.BCM)
     
def RCtime (RCpin):
	reading = 0
	GPIO.setup(RCpin, GPIO.OUT)
	GPIO.output(RCpin, GPIO.LOW)
	time.sleep(0.1)

	GPIO.setup(RCpin, GPIO.IN)
	# This takes about 1 millisecond per loop cycle
	while (GPIO.input(RCpin) == GPIO.LOW):
		reading += 1
	return reading

try:
	while True:
		print RCtime(17)

except KeyboardInterrupt:
        GPIO.cleanup()