low power designe
I have tested the lightsensor(2.0) 's Electric current（int 5v）about 6.5ma,if use 1500mAh 18650 Li battery，it can work about 10 days。How to increase the working hours? thanks!
The trick is to let the Arduino (and radio) sleep.
https://www.mysensors.org/build/battery should give you a good start. Things are slightly different in MySensors 2.0 (the link is for 1.x) but you just use sleep() instead of gw.sleep().
Everything you need to know and understand is written by Nick Gammon:
If you power the Arduino directly (e.g. 2x AA = ~3,00V max) you can use ( http://provideyourown.com/2012/secret-arduino-voltmeter-measure-battery-voltage/ ). This will ofc. not work if you power your setup via VoltageRegulator.
In addition to mfalkvidd's link have alook at https://www.mysensors.org/download/sensor_api_20#sleeping
It describes how to use the sleep function to put the Arduino+Radio in sleep mode.