This study aimed to evaluate the ability of quantitative light-induced fluorescence (QLF) to assess caries lesion activity using visual examination (VE) as the gold standard. Twenty-four visible white spot lesions on buccal surfaces were examined from 23 children, ages 9 to 14 years. At baseline, the surface was hydrated with water, and thereafter, it was dehydrated with continuous compressed air during image acquisition. QLF images were acquired at 0 (baseline), 5, and 15 s. QLF variables [: fluorescence loss (), lesion size (S), : ] was recorded. Changes-in- per second () were determined: , where indicates dehydration time. One experienced dentist conducted VE independently using a dental unit’s light, compressed air, and explorer. and of the active group () were compared with those of the inactive group () using two-sample -tests. As the surface was dehydrated, S and values of the active group increased, whereas of the inactive group showed only a small change. of the active group were larger than those of the inactive group; however, the difference did not reach statistical significance (). Within the limitations of this study, QLF data indicated increments for lesions designated as active and minimal change for lesions defined as inactive.