Spectral Composition and Non-Visual Effects of Light
From a biological perspective, light’s effects are largely driven by the activation of melanopsin-containing photoreceptors and photosensitive retinal ganglion cells (ipRGCs). These cells are involved in regulating the organism’s circadian system and respond primarily to light with higher wavelengths in the cyan region of the spectrum around 480 nm.
The document emphasizes that the biological effectiveness of light cannot be reliably inferred from correlated color temperature (CCT) alone, because light sources with the same CCT can exhibit different spectral characteristics and biological effects. Therefore, it is currently recommended to work with more detailed indicators, primarily spectral composition (SPD), melanopic equivalent daylight illuminance (melanopic EDI), or the melanopic daylight efficacy ratio (MDER).
The Concept of a Spectral Diet and the Importance of Light Timing
The document highlights the concept of a spectral diet, which underscores the importance of light quality and dynamics throughout the day. Proper functioning of the circadian system depends not only on light quantity but also on its spectral characteristics and timing of exposure. Higher morning exposure to biologically effective light supports synchronization of biological rhythms, increases daytime alertness, and contributes to better sleep quality. Adequate exposure to biologically effective light during the day is also associated with improved mood and overall mental well-being.
Spatial Distribution of Light and Simulation of Natural Daylight
In addition to spectral properties, the way light is distributed in space is a significant factor in its biological effectiveness. Lighting systems that combine direct and indirect components, illuminate larger surfaces, and utilize reflections from ceilings and light-colored surfaces can better simulate natural daylight conditions.
