what does the light repersent

This represents the first stirrings of Edna's awakening. She is beginning to realize that she is more than just a wife and mother, that she is an individual wit unique emotions and desires. Awakenig in this respect means that she is becoming aware of her own individuality.

This light seems to represent Edna's gradual realization of her own unconscious coming to the surface. Understood in psychoanalytic terms, she is finally having success in liberating herself from her repressed instincts.