Her are a few excerpts from the interview:
He is here in London filming the latest episode of the Batman franchise, The Dark Knight. It is a physically and mentally draining role - his Joker is a "psychopathic, mass-murdering, schizophrenic clown with zero empathy" he said cheerfully - and, as often happens when he throws himself into a part, he is not sleeping much.
"Last week I probably slept an average of two hours a night," he said. "I couldn't stop thinking. My body was exhausted, and my mind was still going." One night he took an Ambien, which failed to work. He took a second one and fell into a stupor, only to wake up an hour later, his mind still racing.
Here too was his Joker diary, which he began compiling four months before filming began. It is filled with images and thoughts helpful to the Joker back-story, like a list of things the Joker would find funny. (AIDS is one of them.) Mr. Ledger seemed almost embarrassed that the book had been spotted, as if he had been caught trying to get extra credit in school.
The Dark Knight opens July 18th, 2008.