How does a luminometer work?
When a luminescence reaction is set up in a microplate, a luminometer (or luminescence microplate reader), is used to measure the amount of light produced. The microplate is placed in a light-tight read chamber, and light from each well is detected in turn by a PMT. The luminescence readings are expressed as RLU.
In most luminescence applications the total light produced by the sample is measured, without the selection of particular wavelengths. But for other applications like BRET, a luminescence plate reader can be equipped with filters or monochromators that allow the selection of specific wavelengths in order to measure binding or other biomolecular events.