How can i create an opaque glass?

Hello,
How can I create opaque glass?
I am trying to create a shade for a banker's lamp, but the shade is made opaque, which means that the inside of the lamp cannot be seen through. However, if there is light inside, it will let that light through. (Just like a white, opaque light bulb).
If I use Opacity, the inside is completely transparent and I just can't get a good representation of that lamp.

If anyone knows of a solution, I would be glad to hear from you.