Staircase Lighting Control

A simple system using multiple motion sensors and a light sensor to activate stairway lighting at night - and avoid the problem of lights turning out when you're chatting on the landing ;-)
Do you have a large staircase with many floors? This might help you out.
The code is written to be self-explanatory rather than super efficient.
All you need are some cheap components like PIR sensors, a relay and a light sensor and you're off!
The actual components I used were :
Light sensor -
http://www.amazon.de/gp/product/B00VUQ6CU0?psc=1&redirect=true&ref_=oh_aui_detailpage_o04_s00
PIR sensors -
http://www.amazon.de/gp/product/B00Q6OJ8AC?psc=1&redirect=true&ref_=oh_aui_detailpage_o05_s00
Relay -
http://www.amazon.de/gp/product/B005WR753Q?keywords=arduino%20relay&qid=1453024776&ref_=sr_1_2&sr=8-2
Good luck!