A luminometer is provided comprising a waveguide sample holder and one or more detectors. The waveguide sample holder may include a hollow region to hold the sample. The waveguide sample holder can be made of material that guides emission light to a bottom end of the waveguide sample holder. One or more detectors may be provided which detect the emission light coming out of the bottom of the waveguide sample holder. A fluorometer/photometer is also provided that comprises a waveguide sample holder, one or more excitation light sources, and one or more optical detectors. The waveguide sample holder has a hollow region to hold the sample. The excitation light is introduced at an angle or perpendicular to one surface of the waveguide sample holder. The waveguide sample holder is made of material that can guide emission light to the bottom end of the waveguide sample holder. There are one or more detectors that detect the emission light coming out of the bottom of the waveguide sample holder.