Foil for a strand of keratinic fibers and related kit and illumination process

A kit for a strand of keratinic fibers, comprising:

• at least one foil for a strand of keratinic fibers including a first sheet and a second sheet, the first sheet being movable relative to the second sheet between a closed configuration for illumination of the strand and an open configuration, the first sheet being substantially at least partially transparent to the UV-visible light and the second sheet being substantially at least partially opaque to the UV-visible light, and
• a device for illuminating at least one strand of keratinic fibers, the illumination device advantageously comprising a first branch and a second branch defining an illumination cavity, the illumination device comprising an illumination system capable of illuminating the strand,
• the at least one foil having an optical scale arranged on at least one of the first sheet or the second sheet, the illumination device comprising an optical system able to measure a movement of the illumination device relative to the optical scale.