Answer and explanation:
Filmmakers can make use of many resources to establish emotion or settings in a scene, and these resources are all equally important to carry out the important task of conveying the true meaning of every take.
For a sad scene, filmmakers can make use of a sad song, darker lightning, and dialogue that makes the characters reveal their true feelings. For example, in Titanic, when Jack froze in the ocean to save Rose, the music and the lightning really accompanied that moment in which we see Rose trying to wake him up and then finally accepting he died so she could go and be saved by the rescuers in a boat, fulfilling her promise to him.
For a happy scene, brighter lightning and a lively soundtrack will do the trick. In this case, I'm thinking of the scene in the many scenes in the first Harry Potter film, in which Harry discovers how wonderful and interesting the Wizarding World is.