Term used to describe a low-pressure mercury arc possessing a fluorescing layer, which emits in the
UV-A region (from 315 to 400 nm).
Source:
PAC, 2007, 79, 293. 'Glossary of terms used in photochemistry, 3rd edition (IUPAC Recommendations 2006)' on page 440 (https://doi.org/10.1351/pac200779030293)