This is in particular relevant for LEDs, as most of the flux not entered into an LGP will be lost. [0005] In some applications, there is a further requirement for an additional collimation of the source radiation for a more effective subsequent extraction in an LGP. In this case, as is illustrated in FIG. 1B, an LED 18 is coupled to a collimating section 20 at an edge aperture 22 having an edge ap