Light: A very detailed article, in several sections.
Part 1: The basics
Part 2: Light direction
Part 3: Natural Light
Part 4: Artificial and indoor light
These articles are the basis of a book which is out now. If you enjoy the tutorial then the book offers an extra 11 chapters of information, covering everything from shadows, reflections, colour and finally how to use lighting for staging and storytelling.
The book can be found on Amazon and is available in English, French, Italian and Chinese editions. Search for: Light For Visual Artists by Richard Yot or click on the links below.