Just popping back around to say that I spent an interesting and productive half-hour on the great wide internet this afternoon educating myself about light-blocking window treatments.

Since my need is more aesthetic than health-critical (I sleep soundly with city light seeping in), and my space is sadly limited, I'll probably go with some kind of fitted blackout cellular shades. They seem to provide good light-blocking while taking up a very tight, small profile--and they have top-down and bottom-up opening, so very desirable for privacy in urban conditions.

So again, thank you for alerting me to this issue and some cool solutions.