Power naps, the post-lunch snoozes advocated by Winston Churchill, Albert Einstein and George W. Bush, can be as refreshing as a good night’s sleep, according to a study.

Scientists have shown that a 60- to 90-minute siesta can charge up the brain’s batteries as much as eight hours tucked up in bed. But in order to get the full benefit, dozers need to spend some of that time dreaming, the study found.

The findings come from psychologists at Harvard University, who tested the visual learning ability of volunteers.

The tests, which involved watching and then recalling the position of bars on a computer screen, were carried out at 9 am and 7 pm, and again at 9 am the following day. Test scores of volunteers not allowed to sleep during the day fell by the evening of the first day. But the reaction times of people who took a 60- to 90-minute sleep during the day improved in the evening, the report in Nature Neuroscience said.

Short naps only worked when they included two kinds of sleep — slow-wave sleep and rapid eye movement sleep. The two kinds of sleep are categorised by different brainwave patterns and are thought to help the brain rehearse and process new skills and information learnt during the day. The scientists, led by Sara Mednick, said: “From the perspective of behavioural improvement, a nap is as good as a night of sleep for learning on this perceptual task.”