@ Nexus: Yes, the GL refers to OpenGL. It is a bit too different from LTBL to have the same name I think, since it isn't merely an improvement over LTBL, but an entirely different way of doing things.
SFML is used mostly for windowing and input, all the rendering is done manually with OpenGL.
For now, GLLight2D is real time @60fps / resolution of 900x600 on a moderate rig and remains dynamic but looks grainy unless you let it sit there and accumulate samples for a bit. If this is unacceptable, you could then just use it for computing static lighting on level load (a 2D light map). That, or you could just use a blur shader and blur away the graininess (although it doesn't look quite as good then).
Some technical details:
The scene is actually 3D with an orthographic projection. The scene is stored in a BSP tree, with all triangles stored in the leaves (duplicates are made if necessary). The tree, triangles, and material data are all loaded into OpenGL texture buffer objects for random access in the shader. Samples are accumulated in a GL_RGB32F FBO. Global illumination is rendered using a random Monte Carlo path sampling technique (that's where the graininess comes from).
