The question is not CAN the FA demand this, but should they, just because YOU prefer it.

Add me to the list who think that the supplied reading lights are often inadequate, and who don't like spending a long daytime flight feeling like I am in a cave.

I bring eye shades and earplugs when I plan to try to sleep on a flight, since I don't think it is practical, or reasonable to try to impose my preferences (window shade up/down, talking/no talking, reading lights on/off) on a plane load of other people.

Not surprisingly, this topic has been covered before:
http://www.flyertalk.com/forum/showthread.php?t=149410
http://www.flyertalk.com/forum/showthread.php?t=201209
http://www.flyertalk.com/forum/showthread.php?t=830896
http://www.flyertalk.com/forum/showthread.php?t=295550
http://www.flyertalk.com/forum/showthread.php?t=157809
http://www.flyertalk.com/forum/showthread.php?t=440583
http://www.flyertalk.com/forum/showthread.php?t=411816
http://www.flyertalk.com/forum/showthread.php?t=436405