The Raiders of the Lost Ark is a wonderful movie for lighting sequences.  Much of the film uses low key lighting for the dramatic, more frightening scenes.  By using this style in these scenes, the view gets the ominous feelings and the uncertainty that Indiana Jones feels walking through the cave in the opening scene.        
 As he runs for the exit and the giant boulder appears (above) the lighting focuses on that boulder, which makes the viewer feel the danger and gets their heart pumping.  Throughout the movie, Indiana Jones is thrown into dangerous scenes where the lighting helps show the peril of the scene as you see in the snakes scene (below).
   
  This scene's lighting sets the theme of how Indiana Jones fears snakes, and the focus is completely on the danger.  Of coarse there are lighter parts of the movie that the theme is not as ominous, but the most memorable scenes are what makes Indy, Indy.

      The lighting plays perfectly into the action/ adventure genre.  The lighting makes you feel the intensity of the scene and gets your heat pumping fast as action movies should.

      Had this film relied on different lighting such as high key lighting in the dramatic dangerous scenes, the viewer wouldn't have felt how Indy way did about the snakes.  Just think, they open the cavern and instead of darkness and lightning, you see brightness and snakes.  It would not have the same effects.  The low key lighting really sets the mood of the scenes.

References:

                    Image retrieved from

                    http://pyxurz.blogspot.com/2011/08/raiders-of-lost-ark-page-1-of-8.html 

                    Video retrieved from Youtube 

                     http://www.youtube.com/watch?v=ClwIj3x24Q4