Age and Illumination in Digital Reproductions of Eight Louvre Paintings: An Observer-Model Study of Lighting Scenarios and Their Exposure Cost

Museum lighting is specified for a standard observer, yet the retina of a 75-year-old receives less than half the light of a 25-year-old’s. This modelling study applies an age-dependent observer (CIE 170-1 fundamentals with the ageing lens, theWatson–Yellott pupil, two-stage chromatic adaptation and the CIE 146 glare factor) to public-domain reproductions of eight Louvre paintings under 50–500 lx. Three endpoints are kept apart: lens-corrected retinal illuminance, modelled colour appearance (CIEDE2000) and the fraction of picture area below 3, 10 or 30 td. Relative to a 25-year-old, retinal illuminance is 0.70 at 50 and 0.42 at 75 years, equivalent to dividing the illuminance by 2.4; the area below 10 td at 75 years ranges from 10% for the Wedding at Cana to 85% for Saint John the Baptist. Illuminance presets of 1.5 and 2 times within 250 lx recover most of the 50-year deficit for 11–22% more daily exposure in a two-hour slot, whereas a Duv −0.02 spectrum adds 30–41% damage-weighted exposure without benefit. Photographs of the 2024 cleaning of Liberty Leading the People cannot separate a varnish effect from white balance. Sensitivity to all uncertain inputs is reported, and the perceptual test needed is specified.