An interesting contrast on my last trip. The way back, on AA day flight JFK/LHR in W, completely dark all the way. And the reading lights in the 772 are fairly useless, as they were set up for the old 2-5-2 Y seating. Outbound BA LGW/JFK in J, bright daylight all the way, and it appeared similarly in all cabins. It helps probably that BA has a rule about shades open for take-off and landing.