Being tired 'makes you more likely to tell lies'
People who rise with the lark are more likely to lie and cheat in the evening, American researchers have found.
And night owls are more likely to behave "unethically" in the morning.
So it might be a good idea to enjoy your full eight hours, because when a person's energy levels are depleted, dishonourable temptations become harder and harder to resist.
A summary of the findings, published in the Harvard Business Review, stated: "There is mounting evidence that good people can be unethical and bad people can be ethical, depending on the pressures of the moment."
The researchers examined the relationship between energy patterns and ethics.
They focused on the circadian rhythm, which controls wakefulness and sleep and varies across individuals.
And they predicted that these different sleep rhythms would be reflected in different patterns of ethical and unethical behaviour throughout the day.
Researchers tested behaviour in the morning by asking participants to complete a matrix task in which they were paid extra money for each additional matrix they said they solved.
They discovered that night owls were more likely to cheat than early risers.
Researchers suggested that businesses could learn from their findings by allowing employees to work hours that best suit their circadian rhythms.