Luminous yarn is a specialized textile material engineered to emit light in low-light conditions after being exposed to a light source. Unlike reflective materials that bounce back external light, this type of yarn actively glows from within due to the presence of photoluminescent agents integrated into its structure. The most common technology used involves strontium aluminate pigments, which are inorganic, non-radioative, and exhibit persistent phosphorescence. These advanced pigments are notable for their extended glow duration and brightness compared to older zinc sulfide-based materials. The process of creating luminous yarn involves embedding these fine, photoluminescent particles directly into the polymer matrix of synthetic fibers like polyester, nylon, or acrylic before they are extruded and spun. This ensures the glow property is a permanent characteristic of the yarn itself, not merely a surface coating.

The core mechanism of this phenomenon is photoluminescence. When photons from ambient light—whether sunlight, fluorescent, or LED light—strike the pigment particles within the luminous yarn, they excite electrons to a higher energy state. After the light source is removed, these electrons return to their ground state gradually, releasing the stored energy as visible light over an extended period. This results in the characteristic afterglow of the luminous yarn, which can last for several hours depending on the quality and concentration of the pigments, as well as the intensity and duration of the initial "charging" light exposure. The emitted light is typically in a greenish-blue spectrum, as these wavelengths correspond to higher visibility in low-light human vision, though other colors can be engineered.

Manufacturers produce luminous yarn in various forms to suit different textile applications. It can be made as a standard spun yarn for weaving or knitting, or as a filament yarn for finer, smoother fabrics. The yarn's performance is evaluated based on key parameters: afterglow brightness, duration, and charging speed. A high-quality luminous yarn will charge quickly under typical indoor lighting and maintain a perceptible glow throughout the night. This functional yarn must also maintain acceptable textile properties, including tensile strength, flexibility, and dyeability. Often, the base synthetic fiber is chosen for its compatibility with the phosphorescent pigments and its ability to protect them from environmental degradation. The integration of this technology creates a versatile luminous yarn that moves beyond novelty into the realm of functional safety, design, and artistic expression, providing a built-in, energy-free source of illumination within the fabric itself.