1910 New Catholic Dictionary
The light that is kept burning, usually suspended in the middle of the sanctuary, before the tabernacle in which the Blessed Sacrament is reserved. The custom dates from about the 13th century. According to present ecclesiastical legislation, at least one lamp must burn continually before the tabernacle; several may be used, but their number should be uneven. The sanctuary lamp should be fed with olive oil or bees wax; but where olive oil cannot be obtained, the ordinary may permit the use of other, if possible vegetable, oils. Only in extreme necessity may the ordinary permit the use of an electric light. No special color is prescribed; in English-speaking countries a red lamp is generally used.
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Entry for 'Sanctuary Lamp'. 1910 New Catholic Dictionary. https://www.studylight.org/dictionaries/eng/ncd/s/sanctuary-lamp.html. 1910.