ABSTRACT
The vector flux can also be related to the etendue. The vector flux lines cannot cross. If they did cross, this would mean that, at a given point, people would have two flux vectors pointing in different directions, since people can only have a value of the vector flux vector at each point given by expression in the three-dimensional case or expression in the two-dimentional case. The vector flux can be used as a tool to obtain ideal concentrators. The chapter considers some simple examples of non-imaging optics obtained by taking flow-lines generated by Lambertian sources. The vector flux points in the same direction as the flow-lines. If the flow-lines are straight, the direction of the vector flux is the same as that of these lines. If the flow-lines are curved, then the vector flux is tangent to the flow-lines.
