A mercury lamp is described which will operate on any D. C. source maintaining as high a potential as say 25 volts, and give an intrinsically brilliant source of capillary tube dimensions and suitable for laboratory, demonstration, and research work.
E. L. HARRINGTON, "A LOW VOLTAGE, LOW WATTAGE MERCURY LAMP," J. Opt. Soc. Am. 7, 689-689 (1923)