Should natural light in apartments be more tightly regulated?

For similar reasons, I doubt that reliance on artificial light is a significant issue either. In any event, these are invariably very small rooms; lighting them during the day with a 5w LED globe while they're in use isn't a big problem. The big users of power are heating, cooling and cooking.

As for bathrooms and corridors within apartments, residents spend so little time in them it's hard to take this suggestion seriously; it looks like zealotry.

Wrap-up

I haven't yet seen a compelling reason why additional regulation is required to increase natural light within apartments. More consumer information would help, but I think prospective tenants and buyers are perfectly capable of using their eyes to decide what's acceptable to them.

As I noted recently, the focus of regulation should be on what future residents can't reasonably know, can't reasonably foresee, or is outside their control (see Will higher standards make apartment residents worse off?). Ensuring apartment blocks are separated by a reasonable distance from other buildings will do a lot to improve access to daylight.