Light Problem

I was wondering if someone could help me out. I put an omni light in a box and it shines through the box and illuminates everything. I am trying to create a lamp shade effect. Any ideas what I am doing wrong?

I already found this strange effect using simple flood light - but there's a check box to set that makes shadows for this light.

You need shadows - then the box the light source is in will create a shadow that will prevent illumination of the adjacent box.

Hey thanks for the solution. That worked. But it had to be a spot light. Omni light has the shadows boxed greyed out.