by Elio — Ever since as chil­dren we saw fire­flies emit­ting light at night, we ranked lu­mi­nes­cence high in ex­cite­ment of nat­ural phe­nom­ena. We learned later that other kinds of liv­ing things, such as bac­te­ria, pro­tists, fungi, in­sects, and many oth­ers, are also ca­pa­ble of emit­ting light.