This study demonstrated a quantitative method for assessing the effect of a tooth whitening agent. Forty human teeth were stained with a tea solution, and randomly assigned to two groups (A, B) of twenty teeth. The teeth were subsequently treated with either sodium hypochlorite (NaOCL) or deionized distilled water (DDW) by intermittent immersion (60 seconds on each occasion) in a 1:10 dilution of NaOCL (group A) or DDW (group B). Prior to whitening and following each immersion, the color of the teeth at the stained spot was measured using ShadeEye-Ex Dental Chroma Meter and quantitative light-induced fluorescence (QLF). ShadeEye-Ex instantly gave a numerical value for the stain intensity, chroma (C), which is the average of three measurements taken automatically by the machine. QLF gave a quantitative value for the stain, delta Q (% mm2), following analysis of the fluorescence image of the tooth. Immersion was stopped after four readings when one specimen, in group A, was observed to have regained its natural color. There was a good correlation between C and delta Q with either NaOCL (Pearson correlation coefficient (r) = 0.974; p < 0.05) or DDW (r = 0.978; p < 0.05). With NaOCL, an inverse relationship observed between stain measurements, C (Linear fit correlation (R) = -0.982; p < 0.05) or delta Q (R = -0.988; p < 0.05) and exposure time correlated to a linear fit, but not with DDW. ANOVA showed a significant difference between the means (n = 20) of the reading at the measurement intervals (0, 60, 120 and 180 seconds) for both C (p < 0.001) and delta Q (p < 0.001) with NaOCL but not with DDW. In conclusion, the study highlighted the potential of ShadeEye-Ex Dental Chroma Meter as a tool for the quantitative assessment of the gradual change in shade of discolored teeth by tooth whitening products.