Well it didn't work for me at first, i had a bunch of small light fixtures in a room, and added one light_surface. The light_surface made all the light fixtures in the room to emit light. To make only one of them emit light, i had to use one of the filters. The 'Filter entity name' did it.
Here's what it looks like:
The light on the left is a normal texturelight. It gets its color and brightness from the light.rad file:
+0~GENERIC86R 128 0 0 60000
The light on the right emits light from the light_surface entity. Brightness is the same as the brightness value of the lights file (60000)
Now what i like the most about the light_surface entity is that you can toggle the light on and off or select a predefined appearance or custom appearance without making the actual light it emits look like its light coming from an ordinary pointlight, it MAINTAINS the texturelight look. Awesome.