Light collectors for fluorescence microscopy include slab light guides having a specimen volume such as a specimen well configured to retain a specimen. The specimen volume is bounded by a surface of the slab light guide that permits laterally propagating fluorescence to enter the slab light guide and propagate toward a detection or imaging system. Typically, the slab light guide has an elliptical perimeter and the sample volume is situated at a first focus of the elliptical perimeter. A reflector such as a conical reflector is situated at the second focus so as to direct the collected fluorescence to exit the slab light guide.