First, do no harm: a focus on lighting for healthcare

New evidence shows the central role of light in setting the body clock — from neonatal to end-of-life, acute, and chronic effects, and in supporting shift work. Light is also critical to other physiological functions, including stress, mood, and appetite. Some clinicians even consider lighting to be a medical intervention, with a recent editorial suggesting that current standards constitute a violation of the hippocratic oath: 'First, do no harm'.¹

Circadian lighting mimics the natural progression of the day-night cycle, adjusting intensity and colour temperature throughout the day to support the body's internal clock, known as the circadian rhythm. This rhythm regulates sleep, hormone production, and other critical bodily functions. You may be familiar with the basic functions of the eye: the pupil and lense that flex to focus the light on the retina, the fragile membrane that floats at the back of the eye. These noisy signals are filtered and compressed through multiple layers of cells before reaching the top layer, which acts a relay station to fire a stream of data along the optic nerve to the visual cortex, tucked away safely at the back of the head. Your brain extracts information from that dynamic data feed to generate your experience of a familiar world: faces, places, and pets.

We now know that this classic description is only a small part of the picture: around 5% of that top 'relay station' layer is sensitive to light in its own right. Even when there are no signals from the rods and cones, these intrinsically photosensitive cells are responding to light all on their own, thanks to a protein called melanopsin, which has a peak sensitivity of around 480 nanometers, or 'sky blue'. This non-visual pathway sends signals directly to a cluster of glands at the top of the brain stem to drive a potent cocktail of responses: sleep, mood, emotion, and attention.