Luminometer with reduced sample crosstalk

A detection system for use in a luminometer designed for measuring luminescence in each of a plurality of samples, comprising

• a planar x-y array of sample wells, each having an upper edge structure defining a window through which light can be received,
• photodetector assembly having (i) a stage, (ii), a photodetector head having a means defining an aperture, (iii) means for mounting the photodetection head on the stage for movement of the head in a direction substantially normal to an x-y plane containing said array, toward and away from a sample-reading position at which the detection aperture is substantially isolated from light emitted from adjacent sample wells, when such wells are received in said tray and the detection aperture is aligned with the window of the selected sample well, and (iv) spring means for biasing the photodetection head in a direction substantially normal to such plane toward its sample-reading position, and
• means for relatively moving the photodetector assembly and sample array in a plane which is substantially normal to the direction of movement of the photodetector head toward and away from its sample-read position, to successively align each well in the array with the photodetector assembly, with such relative movement being accommodated by movement of the photodetector head toward and away from its sample-read position, wherein the photodetector head rides in contact over the upper surface of the multi-well array, when said tray is moved with respect to the photodetector head, and the head seats over each adjacent well, at a sample-reading position, when the detection aperture is aligned with the window of that sample well.