Abstract: An apparatus for determining a characteristic of a photoluminescent (PL) layer comprises: a light source that generates an excitation light that includes light from the visible or near-visible spectrum; an optical assembly configured to direct the excitation light onto a PL layer; a detector that is configured to receive a PL emission generated by the PL layer in response to the excitation light interacting with the PL layer and generate a signal based on the PL emission; and a computing device coupled to the detector and configured to receive the signal from the detector and determine a characteristic of the PL layer based on the signal.