Understanding the colour spectrum.

Jonathan Rush

Jonathan Rush, Partner

The birth of circadian lighting.

Part two of our five-part series exploring the latest thinking in circadian lighting – in celebration of the International Day of Light on 16 May. Read part one here.

We established in part one that lighting design can have a fundamental impact on our health and wellbeing. To unlock why this is the case, it’s important to understand the colour spectrum of daylight.

Daylight colour spectrum

The simplified diagram above shows how daylight changes from a warmer colour spectrum in the morning, to blue (the dominant spectrum in daylight) during the day, and then back again come evening.

Our eyes and brain receive prompts from this natural day/night cycle, and tell our bodies when to be awake and when to sleep. So it follows that bright blue light in the evening can disrupt sleep, and dark, warm-light interior environments during the day can reduce alertness.

Intense bursts of blue (or even red) spectrum light can temporarily increase alertness and concentration in a similar way to a cup of coffee… they act as a stimulant.

In circadian lighting terms the most sensitive wavelength appears to be in the blue spectrum: about 480 nanometres (nm). The importance of blue spectrum lighting is not new; in the late 90s, research by lighting manufacturers suggested a punch of blue spectrum light to stimulate workers. Although ethically one may question if this was the right approach.

A trio of drivers.

However, more recently, the demand for wellbeing-focused spaces has gathered pace and, alongside it, our circadian system and its impacts on our health has been researched in greater depth. With LED light sources comes the ability to dim and colour mix, and together this trio has driven an enthusiasm about the installation of dynamic lighting systems that mimic the spectrum of daylight… circadian lighting.

You may have seen this concept: a lighting system, usually for offices (but sometimes schools or care environments) that carries out a colour temperature and illumination change throughout the day.

Circadian Lighting for Astra ZanicaOur circadian lighting design for Astra Zenica, in spaces where natural daylight couldn’t be the dominant light source.

A circadian lighting system is, in essence, an artificial ‘sunrise to sunset’ that travels through illuminance levels and colour spectrums from a warm colour spectrum (2,700K) to brighter, cooler (6,500K and upwards) and back again.

The thinking is that, by providing appropriate-intensity blue-spectrum light during main daylight hours and warmer spectrum when the body is gearing up or winding down, you create a suitable environment for melatonin suppression (alertness) and cortisol release to control body temperature.

In part three, I look at what the latest research in circadian lighting tells us, and explore the ethical questions we should be asking.