Light Sensor

Software

You can download the Arduino sketch here:
http://code.mios.com/trac/mios_arduino-sensor/browser/trunk/Arduino/LightSensor

This sensor sleeps most of the time. You can change the sleep interval by updating SLEEP_TIME define at the top of the file.

Wire things up

Follow the instructions in ConnectingRadioModule to connect radio module.

Connect the digital AO (Analog Out) of the light sensor to analog input 0 of Arduino board. Connect VCC to +5V of the Arduino board. GND to GND.

Hardware - Purchase guide

To build this sensor you'll need one arduino + radio specified in the base kit found here:
http://code.mios.com/trac/mios_arduino-sensor/wiki/WikiStart#Buyingguide
With the following additional parts:

1x Light sensor
​http://www.aliexpress.com/item/3-3-5V-input-LM393-light-Sensor-Module-for-Arduino-with-DO-AO-output-w-FREE/976122480.html (You might later need some housing and transformer or battery compartment as well)

TOTAL SENSOR PRICE: $7.6 (arduino + radio) + $2.8 (light sensor) = $10.4