mellojello I've pondered how to get more light in here, but the "best" way to do it would probably bump the bed out one dot and inserting some space between the two (as built, the back of the bed's canopy is two hairs from the window frame at the top). This would also slide the bed out a dot-row, overhanging it out the plate by that one dot row (it's currently flush with the edge).
My mental gymnastics would be to drop a pane of trans-clear (or even colored, if we're thinking of going nutty and creating a stained glass) bricks in a wall between the window and the canopy... and with that, you could drop a pico or two at the base and up-light it. Of course, that's a custom extension of the set itself, but not impossible... the merits of a flexible lighting system.
Personally, while a bit more light would be nice, I'm finding with our build, that dark spot isn't the end of the world... though I totally get after spending a pretty penny for the LEGO set, and another shiny few coins for the lights, one wants it to be as pretty as can be. 😉