Valonkesto

Valonkesto is the Finnish term for photostability or lightfastness—the resistance of a material to fading, discoloration, or other degradation when exposed to light, especially ultraviolet radiation. It describes how well dyes, pigments, polymers, and coatings retain their color and integrity over time.

Measurement and standards: Valonkesto is usually assessed with accelerated aging tests that simulate long-term light exposure under controlled UV and visible spectra. Results are reported as color change (ΔE), loss of strength, or surface changes, following ISO or ASTM methods.

Applications: The concept is central in textiles, paints and coatings, plastics, inks, and art conservation. High valonkesto is sought for outdoor applications, durable goods, and archival materials where color fidelity matters.

Factors: Valonkesto depends on chemical composition, pigment versus dye, binder systems, particle size, and protective additives such as UV absorbers or HALS. Environmental conditions like light spectrum, intensity, temperature, and humidity also influence performance.

Improvement: Manufacturers seek to improve valonkesto by selecting inherently lightfast colors and incorporating stabilizers, while formulation and protective coatings can enhance resistance.

Limitations: No material is completely immune to light degradation. Indoor lighting is often less intense than sunlight, so observed valonkesto can vary with use, exposure, and time.