an instrument for quantitative analysis using a matrix of radiation emitting diodes has means for assuring that a sample receives substantially uniform radiation from each diode . in the preferred embodiment a lens is used to direct the radiation beams to a focal plane where there is a matte surface diffuser backed with an aperture to provide relatively uniform radiant energy field through the aperture to a sample chamber . with this arrangement the same energy distribution contacts the test samples from each of the radiation sources .