luminanzimetri

Luminanzimetri are instruments designed to measure luminance, the photometric quantity that describes the brightness of a surface in a given direction. Luminance is expressed in candelas per square meter (cd/m^2) and is a key parameter in assessing the visibility and appearance of displays, lighting installations, and reflected or emitted light in scenes.

Principle: Most devices use a photodetector whose response is weighted by the human eye's luminosity function (V(λ)). Some meters include spectral filters or multiple channels to approximate color luminance; imaging meters use a pixel array to record a luminance map. Measurements are made for a defined geometry and field of view, and are often calibrated to match standard observer responses.

Types: Spot luminance meters are handheld, with a single or small field of view, suitable for point measurements or quick checks. Imaging luminance meters use a camera sensor to capture a two-dimensional luminance distribution, enabling glare assessment and uniformity analysis. There are also spectrally resolved meters for detailed spectral luminance data.

Applications: Used in display calibration (monitors, TVs, projectors), architectural lighting design and evaluation, automotive interiors, signage and safety lighting, broadcast and film production, and research into visual perception.

Calibration and standards: Luminance meters are calibrated against reference luminance standards traceable to national metrology labs. Accuracy varies with device type but is typically a few percent for professional instruments, with wider ranges for general-purpose meters. Important considerations include spectral match to V(λ), angular response, stray light, dynamic range, and calibration drift. Standards from CIE and ISO define photometric quantities, measurement geometries, and testing procedures to ensure comparability.