Getting to work before sunrise and leaving after sunset during winter months can lead to serious mental health problems, a charity has warned.
Going without daily sunlight can lead to feelings of lethargy and depression which may develop into seasonal affective disorder (SAD), Mental Health Research UK (MHRUK) said.
The warning comes as a poll found that three in 10 adults rise before sunrise during the winter months and return home from work after sunset.
The charity's survey of 2,000 British adults also found that half were concerned that their workplace had little natural light.
And almost one in 10 said they had no access to natural light at all while at work.
Dr Laura Davidson, mental health barrister and trustee of MHRUK, said: "It is estimated that one million working hours are lost each year due to SAD.
"The common unhealthy work culture where lunch breaks are frowned upon is a likely contributor to the increasing numbers of SAD sufferers.
"Employers and educational establishments need to take on board just how important natural light is to good mental health.
"They have a responsibility to ensure that work and study environments have sufficient windows to flood the building with as much natural light as possible.
"Darker areas must be well-lit to address the negative effects of light deprivation."
Seasonal Affective Disorder: The Symptoms
The charity hopes to raise awareness for SAD and depression during its annual wellbeing and awareness campaign Blooming Monday.
On the third Monday of the month, workers are challenged to dress brightly in a bid to combat ''blue Monday'' - researchers claim that the third Monday of January is the most depressing day of the year.
MHRUK said that thanks to a combination of bad weather, debt, the need for Christmas detox and poor motivation, the nation's collective wellbeing is expected to sink to an all-year low on January 20.
It is calling on people to dress in colourful clothing to highlight the plight of those who suffer from the condition and to raise money for research into treatments.
:: To find out more about the campaign visit www.blooming-monday.com.