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 .