We (Yes, both John and I, not the 'Royal we') think it is a normal pendant lampshade....most of these have an outward flared rim which deflects the light into the room and softens or diffuses the light edge.
There would probably need to be a metal flange to protect the glass rim at the small hole side, and reduce the size of the hole to acommodate a normal light fitting.
BTW, I know nothing about lighting..... :usd:
Alternatively, if, as Ivo suggests, it is an uplighter, then the size of the hole and the thickness of the glass are fine.
But it could still be for a Madame's room Paul, :sun:
I still think it is very pretty and could well be French, there are a couple of similar ones on French eBay at the moment.
http://cgi.ebay.co.uk/ws/eBayISAPI.dll?ViewItem&item=190510885680&ssPageName=STRK:MEWAX:ITI meant to add, that I owe you a thank you, beause in looking through all the pages of glass lampshades on eBay for you, I found a matching shade for our landing light....a glass 1970's really funky one that will match the one in the hall.....hehe!! I have to have glass lampshades because I have asthma, and they don't collect the dust, and are easily washed.....I have been looking for a matching one for yonks!!