Definition from Wiktionary, the free dictionary
decalumen (plural decalumens)
- A unit of luminous flux equal to ten lumens.
1956, C. van Duijn, Diseases of Fishes, page 149:
- If the aquarium is placed where it receives insufficient daylight, artificial lighting by means of ordinary incandescent lamps should be employed. For good plant growth 2 decalumens of luminous flux per square decimetre of water surface […]