Finally, workers have a new excuse for stealing pens from the office or using someone else’s milk: early risers and night owls are more likely to display “unethical and deviant” behaviour if forced to work outside their natural rhythms, and should be able to set their own hours accordingly.

Speaking at the Hay festival on Monday about light and circadian rhythms, science journalist and author Linda Geddes called for more workplaces to introduce “flexi-working” to accommodate different chronotypes, which are most often split into two groups: larks, who peak in energy and mood in the mornings, and owls, who perform best later in the day.

Studies have found that logical reasoning peaks mid-morning, problem-solving improves in the early afternoon and all of us experience a post-lunch dip in alertness in the afternoon, she said. However, these peaks and drops were on average, with larks experiencing them earlier and owls seeing them later.

“That’s kind of a problem because research suggests if your manager is a lark and you’re a night owl, they’re going to judge your performance more poorly,” Geddes said. “Lark managers tend to perceive more owlish workers who start later or just don’t get going until 10am, they judge them as less competent. And if you’re an owl forced to start work early, you’re going to curb your sleep.”

Citing a study published in Psychological Science, Geddes continued: “And if you don’t get enough sleep, research suggests you are more likely to engage with unethical and deviant behaviour, such as being mean, bullying your fellow employees or falsifying receipts. But it’s not just owls: the larks tend to behave more unethically in the evening, and owls in the morning. So ideally, you want to introduce flexible working.”

A different study also found that workers who got less than six hours’ sleep per night were also more likely to engage in similar behaviours, with researchers identifying a link between sleep deprivation and glucose levels in the cerebral cortex, the brain region responsible for self-control.

In her book Chasing the Sun, Geddes proposes that flexi-working would “help to level the playing field, it could boost workplace productivity and employees’ health and happiness … such an approach could create a more harmonious and morally sound workplace”.

Describing the British relationship with light as “perverted”, she said that Brits were likely to be deprived of light during the day, spending 90% of their average day inside, while also exposing themselves to too much light at night-time through artificial light sources.

Geddes suggested using gentle light sources like candles and specially designed lightbulbs would “help the body detect natural sleep signals like melatonin and listen to sleep cues”.

“We should be getting more exposure to bright light, ideally by getting outdoors, but if we can’t do that, using artificial lights. And, in the evening, we need to dim the lights,” she said.

In an experiment on their workforce cited by Geddes, the General Services Administration in the US found that employees who were exposed to more daylight, particularly in the morning, took less time to fall asleep, slept longer, and reported better moods. Workers who saw more light between 8am and 12pm slept 20 minutes longer and took just 18 minutes on average to fall asleep – compared to their colleagues’ 45 minutes.