blue light

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Blue light, a pyrotechnic signal.
Blue light on a police vehicle.


blue light (countable and uncountable, plural blue lights)

  1. (historical, uncountable) A mixture of chemicals (including nitre, sulfur and antimony) used in eighteenth and nineteenth centuries for pyrotechnics, night-time signaling and general illumination.
    • 1828, Gray, Samuel Frederick, The Operative Chemist, page 499:
      Blue lights, or blue fire, is a preparation in which zinc and sulphur, or sulphur alone, are used. The particular colour is communicated by the zinc and sulphur.
    • 2015, Ragan, Mark K., quoting Robert Fleming, Proceedings of a Naval Court of Inquiry into the Sinking of the Housatonic, 1864, quoted in Confederate Saboteurs, Texas A&M University Press, →ISBN, page 98:
      When the 'Canandaigua' got astern, and was lying athwart, of the 'Housatonic,' about four ship lengths off, while I was in the fore rigging, I saw a blue light on the water just ahead of the 'Canandaigua,' and on the starboard quarter of the 'Housatonic.'
  2. (countable) A flashing light, usually fitted to an emergency vehicle.
  3. Used other than with a figurative or idiomatic meaning: see blue,‎ light.

Usage notes[edit]

The original chemical mixtures burned with a blue flame. Later versions omitted any colouring agents, producing a bright white light, but retained the name by convention.



Derived terms[edit]




blue light (third-person singular simple present blue lights, present participle blue lighting, simple past and past participle blue lighted)

  1. (law enforcement) To travel quickly in a police vehicle with the lightbar (and possibly the siren) activated.
    • 2011, Donoghue, John, Police, Crime & 999, Troubador Publishing, →ISBN:
      When we weren't blue lighting, we had to obey the 30 mph limit, but out of town we had a training exemption from any speed regulations and were encouraged to push the car to its limits... and we did.
    • 2012, Mukand, Jon, The Man with the Bionic Brain, Chicago Review Press, →ISBN:
      They jumped into his cruiser and blue-lighted it to Boston Medical Center at eighty miles per hour.
    • 2014, Rennie, James, The Operators, Pen and Sword, →ISBN:
      Roger that. Feds and green army are blue lighting to you.