Dictionary: illuminant   (ĭ-lū'mə-nənt)

Something that gives off light.

[Latin illūmināns, illūminant-, present participle of illūmināre, to illuminate. See illuminate.]

Warfare is not confined to daylight. Its prosecution at night is fraught with difficulties, most notably the inability of participants to see either their enemies or their colleagues. Prior to the invention of night vision devices operating in spectra beyond normal sight, simple illumination by artificial light had to be employed. This method still has value, since artificial light may be used to illuminate enemy aircraft, or to ensure that the approaches to defended areas are visible at night, preventing the stealthy approach of an enemy. Primitive illuminants, usually bundles of rags or wood soaked in an inflammable liquid, were used in ancient times. By the 17th century they were known as carcases, and were routinely employed in sieges. At Badajoz in 1812 the French used fireballs to illuminate the breaches, and one eyewitness described ‘the wounded crawling past the fireballs, many of them scorched and perfectly black’.

The most common form of illuminant is the flare. The intense light provided by these devices enables vision, but only briefly. In land operations, the flare is often employed to illuminate attacking troops, to permit their engagement by all those without night vision equipment. Prior to such devices being created, the flare, often attached to a small parachute to slow its descent, and the artillery-fired starshell provided the only means of rapidly illuminating a wide area. Night photography by aircraft relied upon powerful flares to light the area of interest, but since the light also illuminated the aircraft to the enemy, this practice was abandoned when infra-red devices became widely available. Trip flares, attached to low pickets, can be placed around a position or in an ambush site, and may either be fired when an enemy touches a tripwire or initiated by the defender or ambusher.

The searchlight has great utility for target illumination. This applies especially to air defence, where powerful searchlights make it possible for attacking aircraft to be illuminated for engagement by optically aimed anti-aircraft artillery. Searchlights have uses in maritime operations, particularly the detection of surfaced submarines. This technique was of great value in WW II, with devices such as the Leigh Light proving their worth on many occasions. Maritime patrol aircraft such as the British Aerospace Nimrod and Dassault Atlantique continue to employ powerful airborne searchlights for anti-submarine operations. It is also not uncommon for helicopters used in internal security operations to be fitted with searchlights for the illumination of the ground or of individuals when operations are in progress. Such devices include the aptly named Nitesun, which can be attached to most military helicopters with little modification to the airframe.

The use of illuminants in land warfare has not been without its difficulties. Their use can provide the enemy with a suitable target to aim at, and destroys surprise. Using searchlights has proved dangerous in land operations, since although they can dazzle the enemy, they provide a perilously illuminated backdrop to the attacking troops. Searchlights have been mounted on armoured vehicles, particularly main battle tanks, but the use of such lights invites retaliation. While in defensive situations illuminants can be most valuable, in offensive situations, their use for surveillance and target acquisition can be counter-productive. Only in maritime operations has their offensive use been truly successful, and even here this has been slightly qualified by the inescapable problem that the source of illumination becomes as visible as the target itself once it has revealed itself through the use of an illuminating device.

— David Jordan

The noun has one meaning:

Meaning #1: something that can serve as a source of light