A readhead for illuminating a sample carrier and receiving light from the sample carrier, including a housing for receiving a sample carrier, an array of light sources mounted within the housing in a fixed position relative to the sample carrier, and including first and second light-emitting diodes for emitting substantially monochromatic light of a two different wavelengths, a light guide mounted in the housing between the light-emitting diodes and the sample carrier, and a light detector coupled to receive light from the sample carrier. The readhead also includes a light source for directing excitation light of a predetermined wavelength to the sample carrier, and a light filter positioned between the sample carrier and the light detector and adapted to prevent passage therethrough of the excitation light. The readhead allows both fluorescence spectroscopy and reflectance spectroscopy to be conducted on the sample carrier.