sensor.py

import smbus
import time

# Define some constants from the datasheet

DEVICE     = 0x23 # Default device I2C address

POWER_DOWN = 0x00 # No active state
POWER_ON   = 0x01 # Power on
RESET      = 0x07 # Reset data register value

# Start measurement at 4lx resolution. Time typically 16ms.
CONTINUOUS_LOW_RES_MODE = 0x13
# Start measurement at 1lx resolution. Time typically 120ms
CONTINUOUS_HIGH_RES_MODE_1 = 0x10
# Start measurement at 0.5lx resolution. Time typically 120ms
CONTINUOUS_HIGH_RES_MODE_2 = 0x11
# Start measurement at 1lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_HIGH_RES_MODE_1 = 0x20
# Start measurement at 0.5lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_HIGH_RES_MODE_2 = 0x21
# Start measurement at 1lx resolution. Time typically 120ms
# Device is automatically set to Power Down after measurement.
ONE_TIME_LOW_RES_MODE = 0x23

#bus = smbus.SMBus(0) # Rev 1 Pi uses 0
bus = smbus.SMBus(1)  # Rev 2 Pi uses 1

def convertToNumber(data):
      # Simple function to convert 2 bytes of data
      # into a decimal number. Optional parameter 'decimals'
      # will round to specified number of decimal places.
    result=(data[1] + (256 * data[0])) / 1.2
    return (result)

def readLight(addr=DEVICE):
    # Read data from I2C interface
    data = bus.read_i2c_block_data(addr,ONE_TIME_HIGH_RES_MODE_1)
    return convertToNumber(data)

def main():
    while True:
        lightLevel = readLight()
        print("Light Level : " + format(lightLevel,'.4f') + " lx")
        time.sleep(0.5)

if __name__=="__main__":
    main()