Bryce lighting is kinda weak, there really is no "ambient" lighting as there is in PovRay and other programs. The best you can do is like bladesmith said, use radial light close to the desired source. Some atmosphere will help the effect. Also, if you can find Clay's Volumetric Fire, it's by far the best flames out there. And if you turn up the ambience, it will emit light as you can see reflected on the mans body in the image.