Joker in the light is the object of thousands of people laughing. No one will sympathize with him. The more he tries to please the audience, the more sad he will be. Because no one really understands him. All he knows is that the performance on the stage is another way to vent his sorrow. The applause of the audience is just sympathy for him.
When the scene is over, the Joker in the backstage becomes his real self. He is no longer the happy man. He may shed tears in the moonlight and count his hands for sympathy in exchange for sadness, Finally found comfort. No one really knows him, so everything is just passing away