Abstract: A light hardening device is provided for hardening a light hardenable mass applied for dental purposes that has a first light emitting diode for emitting light at a range of intensities corresponding to a set of wavelengths which at most only partially overlap a range of light sensitivities of a photo initiator comprised in the mass. The light hardening device also includes a second light emitting diode for emitting light at a range of intensities corresponding to a set of wavelengths which overlap the set of photo initiator light sensitivities to a relatively greater extent than the partial overlap of the range of first light emitting diode intensities with the range of photo initiator light sensitivities.