“The effects of light in the evening

This pattern has been seen in other studies too. The General Services Administration is the largest landlord in the United States. Many of the public buildings it manages either were designed to try and boost indoor daylight levels or have been remodelled, so its leaders were keen to find out if this had made any difference to the health of those working inside them. Working with the Lighting Research Center’s Figueiro, they picked four such office buildings, plus the GSA Regional Office Building in Washington DC – a converted warehouse which had little access to natural daylight at that time. Workers were asked to wear a device that collected light data around their necks, as well as to complete daily mood and sleep questionnaires for a week during summer and again in winter.

When the light data started to come in, it was initially disheartening. Despite efforts to boost daylight in the workplace, many GSA workers weren’t receiving it. “Our study revealed that if you are three, four, five feet from the window, you lose the daylight,” Figueiro says. “It’s not just your distance from the window that matters. You have partitions, people pulling the shades. Having a window doesn’t necessarily mean you’re going to get good daylight.”

Probing further, Figueiro’s team divided the office workers into those who were receiving a high circadian stimulus – light that was bright or blue enough to activate the circadian system – and those who were receiving a low stimulus.

Those who received a high stimulus took less time to fall asleep at night and slept for longer. Morning light seemed to be particularly powerful: those exposed to a high stimulus between 8:00 and 12:00 took an average 18 minutes to fall asleep at night, compared to 45 minutes in the low stimulus group. They slept for an extra 20 minutes. Their sleep efficiency was 2.8% higher. And they reported significantly fewer sleep disturbances. These associations were stronger during winter, when people may have had less opportunity to receive natural light during their journey to work.

Until recently, scientists had assumed that our urge to sleep was driven by two independent systems: the circadian system, which affects sleep timing, and a ‘homeostatic system’ which keeps tabs on how long you’ve been awake and ratchets up the pressure to sleep.

Light was known to alter the timing of sleep via the circadian system. But recent work by Samer Hattar at the University of Maryland has suggested that the light-sensitive cells in the eye, which control the circadian system, also connect to the homeostatic system. “We propose that the timing and intensity of light exposure doesn’t only modulate circadian-driven aspects of sleep, but also homeostatic sleep pressure,” Gordijn says.

Daylight also affects mood. Those GSA office workers who were exposed to brighter morning light scored lower on a self-rated scale of depression. Other research has shown that morning light, as well as light during the day, can improve symptoms of non-seasonal depression.

“It probably has to do with being more entrained to the light/dark cycle and sleeping better,” says Figueiro. In her study, those who recorded a high circadian stimulus in the daytime tended to be more active during daylight hours and less active once it got dark, suggesting their sleep was more aligned with their internal clock.

These data are in accordance with office studies in the UK. In March 2007, Dijk and his colleagues replaced the light bulbs on two floors of an office block in northern England, housing an electronic parts distribution company. Workers on one floor of the building were exposed to blue-enriched lighting for four weeks; those on the other floor were exposed to white light. Then the bulbs were switched, meaning both groups were ultimately exposed to both types of light. They found that exposure to the blue-enriched white light during daytime hours improved the workers’ subjective alertness, performance, and evening fatigue. They also reported better quality and longer sleep.

This also fits with my own findings. Immediately after waking and before going to bed each night, I filled out a questionnaire to assess how positive and negative I was feeling. The results suggest that my early-morning mood was significantly more positive during the intervention weeks compared to when I was living normally. There was also a trend towards less negative feelings in the evening.

And although I didn’t officially assess my mood at any other time of day, I felt more energetic and uplifted on those weeks when I spent more time outside. Because of my experience, I’m a convert to outdoor exercise. I’m also learning to embrace the long winter nights: seeing the season as an opportunity to make the house cosy with candles rather than bemoaning the darkness.

Even my daughter is a convert. Towards the end of the experiment, I asked her if she was looking forward to switching the lights back on. "No," she said. "It has been wonderful, because the candles are really relaxing." Instead, it was my four-year-old son who insisted: he wanted to see what he was eating at dinnertime.

Although none of my cognitive test results achieved statistical significance, there was a trend towards faster reaction speeds during the intervention weeks, as well as slightly better performance in a test that involved remembering where a token was hidden in a series of boxes.

Studies by Gilles Vanderwalle at the University of Liège in Belgium and Dijk have shown that exposure to bright light activates brain areas involved in alertness – although in these studies, the effects weren’t long-lasting.

However, in a separate study, researchers at Charité Universitätsmedizin in Berlin discovered that the energising effects of light continued for the rest of the day. When participants were exposed to bright, blue-enriched light in the morning, they reported feeling less sleepy during the evenings, and their reaction speeds were maintained, rather than declining as time wore on. Also, the bright morning light seemed to buffer their body clocks against the effects of blue evening light – a finding which is in accordance with current mathematical models of how light affects the human biological clock and sleep.

It supports the idea that brighter and blue-enriched morning light could be a useful countermeasure to artificial light in the evenings especially during the darker seasons, when less daylight is available. It means we don't necessarily need to spend our evenings in darkness, or stop using our computers and gadgets.

“The effects of light in the evening highly depend on the light you were exposed to in the morning,” says Dieter Kunz, who was involved in the study. “When we’re talking about kids looking at iPads in the evening, it’s having detrimental effects if they’re spending their daytimes in biological darkness. But if they’re in bright light during the day it may not matter.”

It’s ridiculously simple. But spending more time outdoors during the daytime and dimming the lights in the evening really could be a recipe for better sleep and health. For millennia, humans have lived in synchrony with the Sun. Perhaps it's time we got reacquainted.

Linda Geddes is the author of the upcoming book Chasing the Sun: The astonishing science of sunlight and how to survive in a 24/7 world. It will be published by Wellcome Collection in January 2019.

We've barely scratched the surface, and I mean that quite literally – countless fungi will be underground and inside other organisms. These microscopic fungi, or more simply "microfungi", are invisible to the naked eye, and so for a long time have remained under the radar. But that doesn't mean they're unimportant. Quite the opposite.

Yes, some will be pathogens, which can cause disease in plants and animals. These tend to be the fungi that get the most attention, both in terms of public awareness and scientific research, and not without some good reason. With our increased global travel and trade, not to mention our contributions to climate change, we're creating a perfect opportunity for new fungal pathogens to emerge and thrive.

But there's so much more than just the pathogens. There are also the recyclers ("saprotrophs"), which break down organic matter and return nutrients to the soil in the continuous cycle of life and death. We live on a planet of finite resources, so it's thanks to these little fungi doing the work to recycle them that our natural world can exist at all.

Countless fungi play key roles in modern society: they can be a source of medicines such as antibiotics and immunosuppressants, industrial enzymes for detergents and manufacturing and new biomaterials to replace plastics. Even the humble baker's yeast, which underpins our everyday food and drink, can be used in the lab to study human genetics or modified to produce important compounds. And these are just the fungi we already know about – imagine the useful properties awaiting discovery in the fungi we are yet to find.

And maybe most famously there are the symbiotic partners known as mycorrhizal fungi, which form a relationship with plant roots, usually for mutual benefit: they can help the plant take up water and nutrients in return for carbohydrates. These fungi can form vast underground networks of nutrient exchange between plants, popularly known as the "wood wide web". As if that wasn't enough, mycorrhizal fungi also help to increase the amount of carbon stored in the soil, and so play an important role in regulating global climate.

Life as we know it would, quite simply, be lost without fungi.

Hidden hitchhikers

Which brings me to the fungi I study. Mycorrhizal fungi aren't the only ones to be found when we look at plants. All plant tissues contain fungi, in much the same way that us animals have an array of microorganisms living inside us: our "microbiome". These microfungi of plants are called fungal endophytes (endo=in, phyte=plant), and are defined by the fact that they live inside plants without causing any visible symptoms of disease.

The sequencing revolution, which has enabled us to detect otherwise imperceptible organisms from mere traces of their DNA, has transformed our awareness of these microscopic fungi. A single plant individual is capable of hosting countless different fungal species.

As always, however, it's not all that simple. When we find fungal endophytes inside healthy plants, some may be latent decomposers or pathogens – in other words, they are in a dormant state, waiting for the plant to die so that they can decay it, or for an opportunity to cause disease. At the same time, there are other fungal endophytes which we know can actually help their plant host, for instance by improving germination and seedling growth. What we call the endophyte lifestyle is really more of a spectrum of interactions between plants and fungi, with both good and bad consequences for plant health.

It was these fungi, with all their mystery and potential, that captured my interest at the Millennium Seed Bank, which is part of London's Royal Botanic Gardens, Kew. If anything, the term seed bank probably conjures up an image of the Svalbard Global Seed Vault: a vast concrete monolith emerging out of the Arctic snow like some sort of super-villain base.

The Millennium Seed Bank, nestled in the grounds of Wakehurst Place in the UK countryside, is rather less imposing to look at, but perhaps even more impressive inside. Coordinated by Kew, the seed bank is both a physical building – the largest seed bank in the world with over 2.3 billion seeds from almost 40,000 species – as well as a global partnership dedicated to the collection and conservation of seeds worldwide.