Essentially, humans are habituated to life outdoors where the light intensity, colour, and spectral distribution is very different from indoors. Our retina contains not only rods and cones but intrinsically photosensitive cells (ipRGCs) that connect and send signals not to the image interpretation part of our brains but to the hypothalamus, helping to regulate our sleep cycle, our circadian rhythm.
In other words, two lights can look the same and effect the circadian system differently, and human centric lighting should tailor intensity, spectra, distribution, and duration to the natural rhythm of light that you would expect to experience outside on a clear day. Health parameters are often monitored so that the lighting system can tailor the parameters of lighting to the individual exposed to it.
Aesthetics and ergonomics – so important at the design stage of any building – is not only surface deep: lighting can impact on the emotional state of building occupants, and colour rendering, flickering, and other factors can massively influence the way we perceive our surroundings, not to mention the people in them. From social factors like attention span to the more mundane effects of headaches and nausea, anyone who has worked in a suboptimal environment will recognize the importance of light design. For business owners, always looking to optimise productivity and reduce costs, lighting can represent a kind of magic bullet to help solve both problems.
The effects of light on melatonin production are another interesting element here; melatonin production should be low during the day and high at night, but if a person spends all day in a low-light environment then the difference is not so marked. Without the natural delta of low and high melatonin production, sleep quality will almost certainly be affected in residents and occupants who have been exposed to suboptimal light all day. Not only does this impact productivity and sociability the next day, as suggested above. It is generally less healthy in the long term, and can in the aggregate increase sick leave.
Again we see the importance of sensors: in arranging an ideal light system, dynamic luminaries are required, but sensors must be used to monitor the parameters of the environment, and adjust to the presence of occupants, the preferences of different people, and so on. As we strive to optimise building performance, and improve the health and wellness of occupants and residents, we should not forget the widespread desire for configurability, one of the main end user benefits that an optimised building can provide. Lighting is not unique in this respect, but it is an aspect of building performance that has a subjective effect on all the others, and a real effect on occupant satisfaction.
 Truls Lowgren, “Biocentric Lighting: the Way to Benefit Health Through Lighting for the Individual”, Memoori Smart Buildings Series, 17 December 2019