Well its all in the title, it has to light up a room if its all in the corner where the wall hits the roof? Thankyou
Leds often produce a lot of light while having a very small surface, which can become quite annoying to look at. I'd try to mount them in such a way, that you look into the leds as little as possible.
I will cover the leds with the thingy that blurs it I forgot what it is called. Oh yeah diffuser sheet
Pelmet lighting usually consists of lights mounted in a narrow "trough" like a picture rail but closer to the white ceiling so that the lights are not seen directly, but reflect off the ceiling producing a quite uniform illumination.
You need an acrylic cover strip over the the pelmet assembly so you can wipe off dust easily.