An apparatus is provided that is capable of interleaving detection of fluorescence and luminescence signals emitted from a plurality of samples. The apparatus is suitable for analysis of samples containing single cells or tissues up to and including living organisms. It contains an optical assembly or "sandwich" for producing a spectrally pure and spatially dispersed light source for illuminating the sample. The invention also provides a plurality of optical sandwiches that can be variously geometrically arranged and their intensities programmed to create spatially uniform illumination over a large sample. The invention further provides an apparatus having at least one of the optical sandwich and a detector system capable of interleaving detection of fluorescent and luminescent signals when a suitable sample is illuminated by the light source of the optical sandwich. Methods for preparing samples and using the sandwiches, arrays and apparatus, are further provided by this invention. A method for interleaving detection of fluorescent and luminescent signals emitted from a plurality of samples is disclosed.