an apparatus for measuring light in samples using a high intensity light source , is presented . the system utilizes bifurcated fiber bundles to transmit light at the excitation and emission wavelength bands . it also uses a band - pass filter for eliminating extraneous light , including that which corresponds to the excitation wavelength range , while permitting the emitted light to pass to a detector for quantitation . the system employs a shutter to shield the detector while the laser light source is activated , and a controller to intermittently activate the laser light and close the shutter . the apparatus preferably includes lenses for better illumination and read out conditions . the apparatus is employed in luminescence oxygen channeling immunoassays . the method has high sensitivity , accuracy and precision , and the apparatus is highly compact . accordingly , the analyzer can perform assays in nanoliter to microliter sample volumes in standard microplates having at least 96 , 384 or 1536 wells .