What light is best for your body clock?

When it comes to keeping your biological clock running on time, there's no substitute for natural light - especially in the morning. Photo / 123RF

When it comes to keeping your biological clock running on time, there's no substitute for natural light - especially in the morning.

A wave of new science around the health implications of light has prompted architects, building managers and electronics companies to try to better accommodate what's best for our circadian oscillator - or circadian clock as we know it better.

"We all have biological clocks, and it's really important to obtain light at particular times of the day so that we can adjust our clocks to a daily rhythm," said University of Auckland Associate Professor Guy Warman, who will speak on the topic at a symposium held at Massey University's Albany Campus in Auckland this Friday.

"In the past decade or so, there has been increasing awareness of the idea that blue light is particularly good for shifting the clock but nothing is better than sunlight.

"So there's a real imperative for people who are designing buildings to achieve the kind of lighting that can entrain people's clocks."

In hospitals, this has been found to be particularly important.

There is now evidence to show that hospital buildings designed to gain morning light exposure could actually reduce the duration of stays of patients with issues such as depression, or those recovering from surgery.

"So this isn't just about influencing the time in hospital, but also longer-term issues in the community like mood and seasonal affective disorder, and major metabolic issues that lead to cardiovascular diseases, diabetes and potentially even breast cancer."

With constant sleep deprivation and disruption come risks of high blood pressure and stroke - and even short-term sleep disruption came with a higher risk of weight gain.

"So there's a real imperative for people who are designing buildings to achieve the kind of lighting that can entrain people's clocks," says Associate Professor Guy Warman. Photo / File

Experimental studies have suggested this is because the hormones that regulate our appetite change, altering our levels of fullness and making us more likely to reach for those heavy, carb-loaded foods that pack on the kilograms.

Sleep loss was also the most common cause of driver fatigue and, in 2014, it accounted for more than 500 crashes on our roads - 31 fatal - and around $268 million in related costs.

Until relatively recently, it was thought our biological clocks could only be adjusted by photoreceptors in the human retina that allow us to see, called rods and cones.

But now we understand that there is another part of the eye, called retinal ganglion cells, which include a subset that are directly photoreceptive themselves and are particularly sensitive to blue light.

"We've really understood how the clock is adjusted on a daily basis by light far more in the past decade, and there have been increasing efforts to work out ways to treat people who have clock disorders with light therapy," Warman said.

"But when you compare the effect of light therapy to that of natural light, it is natural light that is far more potent."

While a well-lit building might have between 500 to 1000 lux of light, that was still little compared with the 100,000 lux you could get outside at midday.

"So it's not just about buildings looking nice with views outside, it's actually about getting that light into the building, particularly morning light, to keep you adjusted to a normal day."

The intensity factor meant it was extremely difficult to replicate the effects of natural light indoors, but designers were trying to address the issue through using blue enriched light.

"The counter issue to all of this is that it isn't just light in the morning that is important, but the absence of it at night.

"We now know that working on your blue LED screen or watching your TV late at night can actually cause sleep disruption on subsequent days."

Looking at a blue light smartphone screen can effectively reset our internal biological clock to later time, postponing the release of sleep-promoting hormone melatonin, meaning we find it tougher to get out of bed when the sun is up.

This was why companies such as Apple had moved to "orange" screens at night, and many companies in Europe were now selling orange-enhanced night lights.

"While it's going to be enough to see by, it's not going to be enough to shift your clock."

The take-home message?

"Depending on the particular person and their age, it can differ, but generally, morning light exposure is really important to keeping your biological clock to a normal 24-hour-day - and avoiding light late into the night is also important."

Susan Mander, a lecturer at Massey's School of Engineering and Advanced Technology also speaking at Friday's symposium, said people needed to think about sleep patterns, productivity, alertness, and safety when making lighting choices for their homes and workplaces.

"By gathering together minds from across the spectrum of lighting, we start to understand how we can do things better and where more work needs to be done."

She hoped the symposium would ultimately offer a plan for healthy lighting in New Zealand.