Why 18 Degrees?

 

 

 

Image by TWCarlson (Own work) [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons

Why 18 Degrees? - 18 Degrees - Architectural Lighting Design London