The present invention provides a diffuser light blocking device comprising an end cap member (820) having a pocketing feature (821 ) that has a side wall (822) and an end reflective surface (810)； the pocketing feature's shape corresponds to exterior shape of distal portion (830) of a diffuser (800) having a distal end surface (801 )； the pocketing feature engages the distal portion； an overlapping section (815) of the pocketing feature's side wall surrounds the distal portion's side wall (802) and prevents at least 95% of the light output from the distal portion from escaping out of the distal portion's side wall； the end reflective surface blocks any forward propagating light output from the distal end surface and returns at least 80% of light coming out of the distal end surface back towards the diffuser； the end cap member is thermally conductive； the end cap member's length (831 ) and diameter (832) provide an exterior surface area that is at least 1,000% of the surface area of the distal end surface； and the device reduces generation of diffuser irradiance hot spots.
