New optical systems are being developed that aim to determine the extent of demineralization in enamel. In our laboratory we have compared three such systems: a ring illuminator equipped with a laser, a beam splitter also equipped with a laser and an intra-oral camera equipped with a white-light arc lamp. The aim of the study was to compare the ability of the different optical systems to detect small enamel lesions with microradiographic analysis and to determine the repeatability of these systems. Forty human enamel specimens (3mm in diameter) were mounted in acrylic and polished. The specimens were kept moist throughout the study. Each specimen of the four groups was individually exposed to 14 ml of Carbopol demineralizing solution for 24, 48, 72 and 96 h, respectively. The mineral loss of the 40 specimens was assessed with blue-violet light-induced fluorescence. Each image was captured with a video camera and analysed with dedicated software. The measurements were repeated 3 times with complete shut-down of the system in between the measurements. The same measurements were performed with the ring illuminator, the beam splitter and the arc lamp. The specimens were then cut into thin sections and analysed with microradiography. Similar high correlations between microradiography and the light-based analysis systems were found for the beam splitter and the clinical caries camera set-up. The repeatability was best for the beam splitter set-up. This indicates that the light-induced fluorescence measurement technique can be used in different configurations and that the repeatability of the measurements is influenced by the physical stability of the set-up.