The spotlights has a fall off distance from where the light intensity is 100% to where it fades out to zero intensity. This fall off in intensity is controlled with these dials. Look at the light from the spotlight as a cone. The cone has a top angle. If you set the Angle Start to 50, you have a light cone with 100% intensity with a 50 degree top angle. If you then set the Angle End dial to 80, the light becomes less and less intense outside the angle 50 degrees and it has totally faded out at an angle of 80 degrees. The Dist Start/End sliders work basicly the same, but here you control how the light fades at a distance. Set Dist Start to 3 and Dist End to 6, and the light cone has 100% intensity until a distance of 3 "Poser units" from the spotlight. Afer that it fades to zero intensity at a distance of 6 "Poser units" form the source. Hope that made it somewhat clearer :-)