valaisu

Valaisu is a Finnish noun referring to illumination or lighting. It denotes the act or state of lighting a space or subject, either with artificial light sources or by daylight. In contemporary Finnish, the more common word for lighting as a system is valaistus; for photographic exposure the related term is valotus. Valaisu may appear in older texts or in contexts where emphasis is on the visible lighting condition rather than the technical system.

Etymology: valaisu is built from valo 'light' plus the abstract suffix -aisu, forming a notion of a lighting condition or act. Because Finnish often merges terms, valaisu can be found in architectural descriptions, stage lighting discussions, and some photography writings to refer to how light is used to reveal form and texture.

In practice, valaisu encompasses planning and execution of lighting: the choice of light sources, their placement, intensity, direction, and color temperature to achieve a desired atmosphere, readability, or emphasis. In photography or film, the concept overlaps with exposure decisions: how much light is allowed to reach the sensor or film, which affects contrast and detail.

Common related terms include valaistus (lighting in a broader sense), valot (lights), valotustekniikka (exposure technology), and valaisutekniikka (lighting technology). Understanding valaisu involves both artistic considerations, such as mood and composition, and technical considerations, such as luminance, glare, and energy efficiency.

Valaisu remains a descriptive term used in Finnish literature and design discourse, with its practical usage overlapping with specific field terms.