Light and Darkness
As is often the case in literature, light connotes life and death connotes darkness. Clov says he watches his light dying in his kitchen; the unseen character Mother Pegg died of light-deprivation. Beckett's revises this somewhat clichéd trope by making his Seasonal Affective Disordered (SAD) world gray. In this medium shade, the characters hold out minimal hope for life while despairing under death's shade. Hamm's blindness is another gray lampshade. He says he can feel the light on his face, and he cleans his glasses as if they were useful to him. His blindness also lends an extra level of selfishness to his refusal to give Mother Pegg his light.
The two young boys mentioned in the play—the boy in Hamm's story about the beggar and the boy at the end of the play—function as symbols of regeneration. Hamm's story takes place on Christmas Eve, giving the sense that the boy, who may or may not be Clov (Beckett was ambiguous about this in conversation), is a Christ-figure. In fact, Clov's opening words echo Jesus's last words. At any rate, Hamm's story contrasts the withering state of the boy's beggarly father and the boy's youthful blooming. The boy at the end of the play is a more explicit symbol of regeneration—Clov calls him a "potential procreator." Hamm, of course, was also once a boy, the son of Nagg, but the Biblical Ham was the son of Noah. While Noah and his ark is a story of regeneration, Hamm's is one of sterility, and youth is further evidence that existence is cyclical and that Hamm will live forever in static misery.