Why natural light?
We have evolved with light that constantly changes both in intensity and spectral composition, through cycles on several levels (like days, lunar months, or years). It always comes from a black-body radiator: some hot material which emits light according to its temperature. This also includes wood fire, which does not affect our sleep negatively.
In the past decade, much research has been done to discover how various frequencies of the spectrum have specific physiological effects. These effects often act in different directions but through overlapping mechanisms — therefore, they are also in interaction with each other. We still know little about the details and we are far from having a complete map of the spectrum regarding the effects of every frequency band.
On the one hand, this means that light can be used to evoke a desired biological reaction in therapeutic applications (e.g. photobiomodulation: using red and near-infrared light for tissue healing).
On the other hand, electric light with highly unnatural spectra can disturb the physiological balance that our body expects from our light environment. Therefore, the safest option to preserve health is as much natural light as possible.
The role of long-wavelength light in tissue recovery (photobiomodulation)
Deep red light improves declining eyesight through enhancing mitochondrial performance:
Photobiomodulation can protect the retina from oxidative stress, with implications for macular degeneration:
A summary on the many benefits of sunlight through photobiomodulation, including how red and near-infrared light slows down tissue aging:
Ongoing study at Pacific Northwest National Laboratory on the cognitive, mood, and cardiovascular effects of long-wavelength light:
Some positive effects of near-infrared supplementation in the morning:
Different frequency — different effect (in various applications)
Closely adjacent frequency bands can have opposing effects:
Long wavelengths (red and near-infrared) can counteract photochemical harm from short wavelengths (blue & UV):
Red light can compensate for mitochondrial harm by blue light, with relevance to age-related macular degeneration:
Age-related macular degeneration protection index: nothing beats natural light (see Planckian radiators, Figure 4):
Retinal ganglion cells: oxidative stress from blue light reduced by red light: