a table that has a translucent top illuminated from below and is used typically for making tracings or examining color transparencies.
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2019
British Dictionary definitions for light table
printing a translucent surface of ground glass or a similar substance, illuminated from below and used for the examination of positive or negative film, and for the make-up of photocomposed pages
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012