The lighting can help to set the play's tone and mood. Ex; if the lighting is bright it could be a happy moment. If the lighting is dark; it could be an intense moment.
The reason I believe this is because even if there was no lighting, it would still be a setting. You just probably wouldn't see the setting. And if it isn't an interactive play, then the play could just be without an audience and still be a play. I hope this helped you!