Ljusdos

ljusdos, literally meaning “light dose” in Swedish, is a concept used to quantify the amount of light exposure received over a period. It is not a single standardized unit but a contextual measure applied in photobiology, horticulture, medicine, and lighting engineering to describe accumulated light energy or photon exposure that can influence biological or ecological responses.

Calculation and units: The dose is typically defined as the time-integral of irradiance over the exposure period: D = ∫ E(t) dt, giving energy per unit area (joules per square meter, J/m^2). In plant science, a related measure is the daily light integral (DLI), expressed as mol photons per square meter per day (mol/m^2/day). For human-centric applications, spectral weighting is sometimes used to reflect biological responses, as in melanopic lux or circadian light metrics rather than raw energy.

Measurement and considerations: Ljusdos is estimated with radiometric instruments such as lux meters, spectroradiometers, and quantum sensors. Because biological effects depend on spectral content, the spectrum of the light source and timing of exposure are often as important as the total dose, and different fields adopt different conventions for reporting.

Applications: In horticulture, ljusdos helps optimize greenhouse illumination and crop yields; in medicine and architecture, it informs lighting design to support health and comfort while managing energy use; in ecological studies, it serves to assess light pollution and its effects on ecosystems. The term remains descriptive rather than a fixed SI quantity.