Planar VrayLight: Sharp Shadow Edge

[DANIELE_CASAROLA]

Hi!
I need to reproduce the same illumination as you can see in this scanned image (the vertical line in the middle is the middle of the book pages):
http://www.ossosso.com/scambio/shoot_07.JPG

I've some trouble on how to do that... as you can see on the right and on the left the light "draws" sharp edge, but at the same time it is a quite "large" light, not so small.
How can I do it?

Thank you very much.

[viscorbel]

What makes you think there's a planar light in there? You can't exactly see the light source itself. Might as well be a small powerful round bulb (judging from the circular light falloff, it's most likely the case.)