Check out the poser tutorials here, there's a couple on lighting. Nerd3D has one on volumetric lighting using Poser 5. you can fiddle around with ambient colors of objects to make them appear to glow, turn off their ability to cast shadows in order to make them appear as a light source. Spot lights can be XYZ positioned and aimed within Poser. I would try using multiple aimed spotlights outside and around the light source of your oil lamp, with the simulated light source object having a bright ambient color. "Global Illumination" in Poser isn't what you're used to. This effect is being simulated by placing a sphere of multiple, low-intensity infinite lights around the scene (sometimes as many as 20 or 30 lights). The "global illumination" light sets for sale at DAZ3D use this technique. The "ultimate fire" package in the market place is based on simulating a light source using aimed and positioned spot lights and works rather well. Every program has it's learning curve. Some just take more fiddling around time than others. :)