ˌaktəˈnäməd.ə(r) noun
( -s )
Etymology: actin- + -meter
1. : an instrument for measuring the direct heating power of the sun's rays
2. : an instrument for measuring the actinic power of radiant energy usually by means of light-sensitive paper that darkens on exposure to light ; specifically : a photographic instrument for measuring the exposure to be given — compare photometer
• ac·ti·no·met·ric |aktəˌnō|me.trik adjective
• ac·ti·nom·e·try ˌaktəˈnämə.trē noun -es