The effects of exposure of slices of Havarti cheeses to monochromatic light of wavelengths 366 nm, 405 nm, and 436 nm, respectively, were studied by tristimulus colorimetry, solid-phase microextraction gas chromatographic analysis of volatiles, and open-end fluorescence spectroscopy. Having determined the photon fluxes of the three wavelengths by ferrioxalate actinometry, it was possible to quantify the effects of light exposure in an absolute manner. For all analyses, the most severe effects were caused by visible light, leading to colour bleaching, change in hue, riboflavin degradation, and formation of the secondary oxidation products hexanal, 1-pentanol, and 1-hexanol. Apparent quantum yields for formation of hexanal and 1-pentanol were found to be insignificantly different for 405 nm and 436 nm exposures, having values of (3–5).10−5 mol.einstein−1 and (9–13).10−5 mol.einstein−1, respectively. These compounds were not formed when exposed to 366 nm light. In contrast, 1-hexanol was formed when exposing cheese to all three wavelengths, resulting in apparent quantum yields of (2–6).10−5 mol.einstein−1. The results obtained are discussed in relation to the interplay between inherent product colorants, light sources, and transmission characteristics of the packaging materials.