Media playback is unsupported on your device Media caption Two experiments with light are trying to help Swedish citizens cope with the long dark winters - Malcolm Brabant reports

Excessive sun exposure is bad for our health. But sun deprivation is also harmful - contributing to ailments from depression to disturbed sleep, obesity and even cancer.

People inhabiting the far northern hemisphere are particularly vulnerable, forced to endure long, dark winter nights and sometimes only seeing the sun for three quarters of an hour per day in December.

But relief could be on its way, with researchers exploring a range of projects that could bring light to the wider population.

The Lighting Research Center at Rensselaer Polytechnic Institute in Troy, New York is developing a system that could transform people's homes and lives by regulating the amount of light to which they are exposed.

In those countries far from the equator such as Sweden, we have a need for light especially in the morning. Prof Thorbjorn Laike,, Lund University

At its heart is a device known as a Daysimeter, which was developed by a team led by Professors Mark Rea and Mariana Figueiro.

"The Daysimeter is a personal light and activity sensor," says Prof Figueiro, who works at the Lighting Research Center.

"It can be worn on the wrist or around the neck and continuously records and stores data for measuring circadian light-dark patterns."

The device is now being developed further as part of the "Healthy Homes" project.

Working with collaborators in Sweden, the plan is to automatically send the data collected by the Daysimeter to a central control hub based at home.

If a person turns out to have received either too much or too little sunlight, a smart system will adjust the lighting in the home to compensate.

By rebalancing an individual's light exposure, the idea is to help people maintain a more normal and healthy circadian rhythm.

Switched on

Humans are programmed to wake and sleep on a roughly 24-hour cycle, and the timing is regulated by exposure to light.

"Disruption of a regular, daily pattern of light and dark can lead to poor sleep, fatigue and decreased performance," says Prof Figueiro.

I come to school when it's dark, and go home when it's dark. Viola Asbaghi,, Student

"It can also contribute to poor health ranging from obesity, diabetes and cardiovascular disease to certain forms of cancer."

In places where sunlight is in short supply, bright electric lighting delivered at the right time of day can act as a substitute.

At Lund University, in southern Sweden, Prof Thorbjorn Laike shows off what he calls an "artificial sun", a collection of bright bluish lights that wouldn't look out of place in a giant's dentist surgery.

Prof Laike is collaborating on the Healthy Homes project and will be testing the lighting system's effectiveness in Sweden.

"We anticipate that this will make it easier for people, especially people working within shift work, to have better lighting solutions in their home," says Prof Laike.

"But also people who have problems coming up in the morning during the dark period. Because we know that in those countries far from the equator such as Sweden, we have a need for light especially in the morning."

Prof Laike believes architects also need to re-examine and perhaps re-employ the building standards of the 19th century when designers were obliged to maximise the amount of daylight penetrating schools and factories.

Bright future

Image caption Bright artificial light can act as a substitute for the sun

One place in Sweden that has embraced this idea is Dragonskolan school in the northern town of Umea.

They have installed full spectrum lights in seven of their classrooms with the hope that it will help increase alertness and reduce fatigue in its students.

In December the sun shines on average for just 45 minutes a day in Umea.

The town prides itself on its museums and the proximity of outdoor activities like dog sledding and cross country skiing.

But in the depths of winter with its almost constant fog of darkness, a supreme effort is required to escape the shackles of the duvet and central heating.

The dancing multi-coloured light shows of the Aurora Borealis aren't sufficient compensation for the absence of the sun.

"During winter you feel tired and it doesn't feel like it's seven in the morning," says one student, Carl Frederik Valverius.

"It feels like it's 12 in the middle of the night. You just want to skip school and stay in bed. You want to do your best in school and be a good student. But at the same time you don't feel like you have the energy."

Fellow student Viola Asbaghi agrees: "I come to school when it's dark, and go home when it's dark. I never see the light in winter and feel permanently tired."

The power of light

Image copyright SPL Image caption A lack of morning light can have a serious effect on health.

Unlike standard lighting that tends to give off a yellow hue, the so-called "full spectrum" lights installed in these classrooms give off a greater proportion of blue wavelengths.

These have been shown to have a greater effect on regulating the body clock if delivered early in the morning. It works by suppressing the production of the hormone melatonin, which causes drowsiness.

The lights are also much brighter, which has been shown in previous studies to increase alertness throughout the day.

"It's too early to say whether grades will be better but what I'm hoping for, of course, is improved attendance and improved results," says Stellan Andersson, headmaster of the 2,000-student Dragonskolan.

The lights were the gift of a local renewable utility company and run from stored solar energy harvested during a heatwave in July and August last year.

The corridors and other rooms that are conventionally lit are Stygian in comparison.

"It's nice. It's much brighter. I feel rejuvenated," whispers Viola Asbaghi, 18, during a tough English exam in room C151, at just after nine in the morning, when it's still dark outside.

"I feel sharper, more alert, more focused," says Carl Frederik Valverius, also 18.

Bleary eyes

Image caption "You just want to skip school and stay in bed", Carl Frederik Valverius on getting up in the dark.

Previous studies have shown that exposure to bright light can have a marked affect on alertness.

However, Dr Baba Pendse, a senior consultant psychiatrist at Skane University Hospital in Malmo, south Sweden, warns against excessive use at the wrong time of day because it keeps the body wide awake, when it should be slowing down in preparation for sleep.

"If you get light in the late afternoon or evenings, then you are shifting your body rhythms to the other direction, which is pathological. And that's going to cause you problems."

While the students hope to keep bleary eyes at bay, the Healthy Homes researchers plan to kit out the first experimental home within two years, although it could be a decade before the system becomes widespread.

In the meantime, deprived northerners will have to grab light where and when they can.