1) The central open tube in a plant fiber or cell.
2) The unit of light intensity as specified by the International System (SI). One lumen equals the amount of light produced by one candela. In international (metric) units, illumination is measured as lux which is defined as one lumen per square meter. In English units, light is measured by foot-candles which is defined as one lumen per square foot. Since lumen, or light flux, is the same in both cases, one foot-candle is about 10 lux (9.4).
- A Glossary of Paper Conservation Terms, Margaret Ellis (ed.), Conservation Center of the Institute of Fine Arts, New York City, 1998
- The American Heritage Dictionary or Encarta, via Microsoft Bookshelf 98, Microsoft Corp., 1998
- Random House, Webster's Encyclopedic Unabridged Dictionary of the English Language, Grammercy Book, New York, 1997
- Mary-Lou Florian, Dale Paul Kronkright, Ruth E. Norton, The Conservation of Artifacts Made from Plant Materials, The Getty Conservation Institute, Los Angeles, 1990