Luminescence is produced by either a biological or chemical reaction, such as an enzyme and its substrate. Its resulting light can be detected by a photomultiplier tube (PMT), where photos are converted into electrons with the resulting current being proportional to the light. After a luminescence reaction is assembled on a microplate, the luminance sensor (emit UV light at a certain wavelength) is utilized to measure the quantity of light produced. The microplate is placed in a light-tight chamber in order for the light (or photons) from each well to be detected by a PMT. Luminescence readings are measured as RLU (relative light units). Luminescence detection differs from and is simpler than fluorescence detection due to the fact it does not require a light source of excitation or optics for choosing distinct excitation wavelengths. In a broader sense during luminescence, matter emits light of a wavelength without emitting heat, and returns to the ground state after its excited state absorbing energy from heat, friction, or an electromagnetic wave.