Optical-State Characterisation and Drift Detection in Vat-Photopolymerisation Equipment: Spatial Irradiance, Spectrum and Divergence, and the Unclosed Ageing Question

This Engineering Review treats the optical state of LCD-based vat-photopolymerisation equipment as a spatial, multidimensional quantity rather than a nominal wavelength and average irradiance. It defines a bounded architecture for baseline mapping and drift detection across irradiance, spectrum and divergence, and distinguishes baseline non-uniformity, temporal drift and ageing attribution. The review explains why grayscale correction can reduce irradiance non-uniformity without correcting divergence and why optical mapping does not replace formulation-specific conversion, dimensional or functional measurement. It does not propose a universal drift threshold, measurement interval, ageing rate, service life, replacement interval or decay model because directly read longitudinal evidence was not recovered.