glühen

Glühen is a German verb meaning to emit light as a result of high temperature, i.e., to glow or be incandescent. It is used for objects that become hot enough to give off visible light, typically appearing red or orange, such as embers, metal heated in a forge, or a filament in an electric lamp. The term can also be used figuratively to describe intense heat, emotion, or activity.

Grammatically, glühen is intransitive. Its present tense forms are ich glühe, du glühst, er glüht. The simple past is glühte, and the perfect tense is formed with haben as hat geglüht (e.g., Das Metall hat geglüht).

In metallurgy and materials science, Glühen refers to a controlled heat-treatment process in which a material is heated to a specific temperature and held there before being cooled, with the aim of changing mechanical properties, relieving internal stresses, or refining the grain structure. Common variants include Weichglühen (soft annealing), Normalglühen or Normalisieren (structure normalization), and Spannungsfreiglühen (stress relief).

In everyday language, glühen describes both physical glow and metaphorical brightness or intensity. For example, Kohle oder Draht kann glühen, and the phrase glühend vor Wut or die Glut der Begeisterung conveys strong emotion.

Etymology traces the word to historical Germanic usage, with cognates in related Germanic languages referring to glow or heat. The noun form das Glühen denotes the glow itself or the process of glowing.