Z, P, and I were in Sherbrooke, delving into the possible differences and chronology of dusk versus twilight in an in-depth conversation over oysters and burgers. Apparently, the research continued after they dropped me off as the next day there was an email link to a new website:
http://diurnalillumination.weebly.com
A mere preview of the knowledge to be gleaned!
Check it out and find out everything you ever wanted to know (er, and MORE) about diurnal illumination.