A description is given of the use of naphthalene-1,8-dicarboxylic monoimides of the formula (I), in which R.sup.1 is hydrogen, alkyl, alkenyl, cycloalkyl, cycloalkenyl, heterocycloalkyl, aryl or heteroaryl and R.sup.2 is a radical containing at least one .pi. electron system containing a carbon atom and at least one further atom selected from carbon, oxygen, and nitrogen, with the proviso that the radical contains at least one atom other than carbon; to protect organic material from the damaging effects of light, of compositions which comprise at least one naphthalene-1,8-dicarboxylic monoimide of the formula (I) in an amount which provides protection from the damaging effects of light, and at least one organic material, and of new naphthalene-1,8-dicarboxylic monoimides (I).