Mercury-vapor lamp

A 175-watt mercury-vapor light approximately 15 seconds after starting.
A closeup of a 175-W mercury-vapor lamp. The small diagonal cylinder at the bottom of the arc tube is a resistor which supplies current to the starter electrode.

A mercury-vapor lamp is a gas-discharge lamp that uses an electric arc through vaporized mercury to produce light.[1] The arc discharge is generally confined to a small fused quartz arc tube mounted within a larger soda lime or borosilicate glass bulb.[1] The outer bulb may be clear or coated with a phosphor; in either case, the outer bulb provides thermal insulation, protection from the ultraviolet radiation the light produces, and a convenient mounting for the fused quartz arc tube.[1]

Mercury-vapor lamps are more energy efficient than incandescent lamps with luminous efficacies of 35 to 55 lumens/watt.[1][2] Their other advantages are a long bulb lifetime in the range of 24,000 hours and a high-intensity, clear white light output.[1][2] For these reasons, they are used for large area overhead lighting, such as in factories, warehouses, and sports arenas as well as for streetlights. Clear mercury lamps produce a greenish light due to mercury's combination of spectral lines.[2] This is not flattering to human skin color, so such lamps are typically not used in retail stores.[2] "Color corrected" mercury bulbs overcome this problem with a phosphor on the inside of the outer bulb that emits at the red wavelengths, offering whiter light and better color rendition.

Mercury-vapor lights operate at an internal pressure of around one atmosphere and require special fixtures, as well as an electrical ballast. They also require a warm-up period of four to seven minutes to reach full light output. Mercury-vapor lamps are becoming obsolete due to the higher efficiency and better color balance of metal halide lamps.[3]

  1. ^ a b c d e "What color is mercury discharge tube? – handlebar-online.com".
  2. ^ a b c d Schiler, Marc (1997). Simplified Design of Building Lighting, 4th Ed. USA: John Wiley and Sons. p. 27. ISBN 978-0-471-19210-7.
  3. ^ Gendre, Maxime F. (2011). "Two Centuries of Electric Light Source Innovations" (PDF). Eindhoven Institute for Lighting Technology, Eindhoven Univ. of Technology, Eindhoven, Netherlands. Retrieved April 3, 2012. {{cite journal}}: Cite journal requires |journal= (help)