I've been thinking about this all afternoon! I would have never struck on an obsession with light! I did however take note of where they were walking and what was along their path! Mostly as I was reading, I was immediately caught up in the people...not just the main characters, but the clerks and other working class going about their business and what I assume was their irritation of Ridley and Helen getting in the way and slowing down that business. Then watching the relationship between Ridley and Helen start to unfold and getting a sense of anguish from both of them, even though exhibited in different ways. Then seeing how Helen assessed the people around her as being somewhat trivial, but not willing to think that she is a completely hard woman as you see her brightening up at the mention of her children!
I will definitely be reading this chapter again...intrigued about your speculation of what meaning might be behind, as you put it her obsession with light!