The scientist Robert Boyle also reported on some of his work on triboluminescence in 1663. Additionally, mechanisms relating to triboluminescence, chemiluminescence, and electroluminescence have been suggested. "Fractoluminescence" is often used as a synonym for triboluminescence. A historically important instance of triboluminescence occurred in Paris in 1675. "N"-Acetylanthranilic acid exhibits triboluminescence when crushed. The biological phenomenon of triboluminescence is conditioned by recombination of free radicals during mechanical activation. Triboluminescence can be observed when breaking sugar crystals and peeling adhesive tapes.