Biochemical assays of samples in receptacles, in gels, in blots, in arrays and the like, and that utilize excitation and light emission as labels for detection are enhanced by an illumination and detection system that supplies excitation light through an optical fiber that transmits excitation light from an excitation light source to the sample. Emission light produced by the excitation is then collected by a lens and converted to a signal that is compiled by conventional software for analysis. The optical fiber transfixes (passes through) the lens via a slot or other opening and is preferably offset from the center of the lens. The optical fiber and collecting lens can either be on the same side of the sample or on opposite sides, i.e., one above and the other below. The optical fiber and the light collecting lens are arranged such that the direction of travel of the excitation light and the direction along which the emission light is collected are not coaxial, and preferably both are at an acute angle to the axis normal to the mouth of the receptacle. Illumination systems are also disclosed in which a ultraviolet, visible, or near-infrared light source is optically coupled to an optical fiber.