36 | New Scientist |1 June 2019
message that it is night, including to parts of
the brain that promote sleep. A 2016 study
found that people living in areas with elevated
levels of light pollution tend to go to bed and
wake up later than those living in darker areas.
They also sleep less, are more tired during the
daytime and are less satisfied with the quality
of their sleep. That is a worry when the area
of Earth’s outdoors that is artificially lit is
increasing by more than 2 per cent a year,
according to a recent study of satellite images.
Experiencing a marked contrast between
day and night is important. Our light exposure
influences the amplitude of our biological
rhythms: they become flatter under more
constant light conditions, which has been
associated with poorer sleep. So what can
we do about it?
The General Services Administration is an
independent agency of the US government
that oversees the management of
government-owned buildings, making it the
largest landlord in the US. Its bosses wanted
to establish whether designing more daylight
into their buildings affected the occupants’
well-being, so they asked Figueiro to study it.
The results were initially disheartening: just
a metre or so away from the windows, the
illuminance dropped sharply. When Figueiro
compared office workers’ sleep, she found that
staff who got more bright light during the
day – perhaps because they sat next to a
window, walked to work or spent their lunch
breaks outdoors – fell asleep faster at night
and slept for longer than those who got less
light. Workers exposed to more bright daylight
between 8 am and noon took an average of
18 minutes to fall asleep at night, compared
with 45 minutes in the low-light exposure
group. They also slept for around 20 minutes
longer and had fewer sleep disturbances.
Such improvements have been recorded
elsewhere too. Dutch researchers fitted
20 people with devices to record daytime
light exposure and then assessed their sleep
on subsequent nights. Greater daylight
exposure was found to be associated with less
fragmented sleep and more deep sleep, which
you need to feel refreshed in the morning.
Also, “if they did wake up at night, they were
less sleepy the next morning”, says Marijke
Gordijn at the University of Groningen.
There are other benefits as well. In the
General Services Administration study, greater
daylight exposure was associated with lower
scores on a self-rated scale of depression. That
is consistent with other findings that bright
morning light can help treat seasonal and
other forms of depression. That was assumedOvercast
nightWaiting roomsClassroomsSupermarketsOperating theatres100,0000.110,00010001001010.010.0010.0001StarlightQuarter moonFull moonDeep twilightTwilightLight intensity
(lux)Very dark dayOvercast dayDAY
NIGHTDaylightDirect
sunshineHomes
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LaboratoriesSOURCE: NATIONAL OPTICAL ASTRONOMY OBSERVATORYThe light in our lives
Even the brightest indoor spaces are dim compared
with the outdoors in daylightto be because light strengthens body clocks,
nudging them earlier, which helps to improve
quality of sleep by becoming more aligned
with when we have to wake. But the link may
be more direct: a recent animal study showed
that the same ipRGCs that feed into the brain’s
master clock also connect to the thalamus,
a brain area related to mood. “It is a hugely
important finding,” says Katharina Wulff,
a daylight researcher at Umeå University in
Sweden. “It shows that light not only affects
the clock, it can directly act on mood.”
Then there is alertness. A 2017 German
study suggested that exposure to bright light
in the morning boosted people’s reaction
speeds and maintained them at a higher level
throughout the day – even after the bright
light had been switched off. It also prevented
their body clocks from shifting later when
they were exposed to blue light before bed.
“The effects of light in the evening highly
depend on the light you had in the morning,”
says Dieter Kunz of the Charité University
Hospital in Berlin, who led the study.People in glass houses
Some researchers are taking it to extremes.
Petersen, in a reversal of his basement flat
days, is one of 12 volunteers who spent three
nights on a Danish island in a glass dwelling
designed to provide inhabitants with full
exposure to the 24-hour light-dark cycle.
The volunteers stayed during autumn
and spring, when the hours of daylight and
darkness are roughly the same. Wulff, who is
leading the study, found they had significantly
higher levels of morning alertness after
sleeping in the glass house. Also, the drop in
melatonin levels in the morning – marking the
end of the biological night – arrived an average
26 minutes earlier, presumably because the
dawn light flooded their sleeping quarters.
“Exposure to light at this time is setting up
the body to be awake, causing the whole
neurochemistry of the brain to be better
synchronised,” says Wulff. She wants to recruit
more people to live in the so-called Photon
Space, including during summer and winter.
For those of us who don’t live under glass,
getting more sunlight in the morning is a
good idea. However, it is still unclear how
much daylight is necessary to optimise health,
and it may well differ depending on what you
are trying to achieve. Half an hour in the
morning may be enough if you want to
stabilise your circadian system, says Figueiro.
“But if it’s for alertness, you may need bright
light exposure for the whole day.”