Lighting Industry Association (LIA): https://www.thelia.org.uk - the primary professional body in the UK for the lighting industry. Offers some useful info on its web page, and paid-for courses. Membership is just for medium or large businesses.
Various US training resources (some free, some paid for): https://www.lightsearch.com/cgi-bin/cosearch.pl?coproducts=online%20training,%20certification,%20continuing%20education and https://www.lightsearch.com/cgi-bin/cosearch.pl?coproducts=information+/+training+center
Light Guide training articles (US centric): https://www.lightsearch.com/resources/lightguides/index.html
List of lighting magazines: https://www.lightsearch.com/cgi-bin/cosearch.pl?coproducts=magazine