Hi there.

You definitely can. My living room is roughly 17' x 14'. I have two sconces along the long wall (opposite walls) and two flanking the flat panel.
The two on the long walls are 300 watt halogens. They light up the whole room- despite the fact that the room has a tall ceiling and terra cotta paint color on the walls and ceiling.

The two flanking the flat panel are more decorative.

You just need to make sure you have a bright fixture- at least a 200 watt halogen. An uplight is good since it'll bounce the light off the ceiling.

I know this is an old post, but Lightguy, where do you find sconces that take 300 watt halogen fixtures? Most of the sconces I've seen you are lucky to be able to use a 60 watt bulb. I would love to be able to get that much extra light as I plan to install some sconces on either side of my television.

If a fixture will take a 60 watt incandescent, there's a good chance you can fit a 42 watt or larger compact fluorescent. This will give you light equivalent to a 150-250 watt incandescent, without the dangerous heat of a high output halogen lamp.

Here is a link that might be useful: 55 Watt CF (an example, not an endorsement)

Thanks to all who posted - i forgot to check back timely, sorry.

Don't know if anyone is stil interested in this, but we're putting up Estiluz A1153 wall sconces which take 200 watt halogen bulbs. We'll have 2 fixtures on each of 2 long walls.
They've been recommended by our lighting designer to use to light up a large living room which is also open to a lrge foyer area, and open to the dining room. Those areas have their own light, but we're hoping some light will also spill in there.
This is a co-op in a large NYC apartment building and we're not allowed to add overhead lighting wilred into the ceiling, which would have been our preference. The many floor lamps we've been using have been ineffective and unpleasant to use;.

It's a large are and we want to be able to hit a switch and light up the room. Instead we have to walk around turning on at least 4 lamps in various corneres, and the light still isn't satifying.

If anyone is interested, I'll let you know how it works out.