A lot of people think that sleep and circadian rhythms are nearly the same thing, but this isn't really true. But there are a lot of other circadian systems in the body, and they can become compromised if you spend all your time as if it's the longest day of the year - e.g., melatonin duration in the blood will expand to use 12 hours during the winter (even if you're not sleeping that long), and melatonin is also pretty good at fighting cancer.
There aren't so many places on the planet where people have 16 hours of bright sunlight, and there are none of them that do this year-round.
We think most people are "darkness deprived" - so a healthy pattern of light includes seeing some lower light levels, even when it's not right before bedtime. We also think that lowering the light several hours before bedtime can help people align with their day, but individuals vary a lot in this.
Overall this is an area we are putting a lot of work into right now - both in showing that this idea is the right thing to do, and in making it more flexible.