The light from the upper left is ambient/ natural light. On the camera left is a column structure (fire escape route)which helps to filter the light onto the subject, a bit like a really tall corridor for the better description. Subject is between two tall structures. The setting is actually quite shady in real life, I just set the light meter on the camera to centre weighted average and got lucky with the result!
Image is taken at the Sydney Convention Centre compound during SMASH!2012