Sleeping less than six hours every night can be as dangerous as not sleeping at all, a new study found. But that's not all. The study participants who slept just six hours a night thought they were fine, which means they thought they weren't sleep-deprived.

A team of researchers analyzed the total cognitive responsiveness of 48 participants every two hours in the period of two weeks. The participants were divided into four groups and had different sleep durations from eight, six and four hours and no sleep at all.

At first, the people who slept six hours did fine but on the 10th day, they became as unproductive as those who didn't sleep for two nights in a row. What's interesting is that the six-hour sleepers weren't aware that their levels of sleepiness were gradually increasing.

In the participants who slept only four hours a day, their daily performance showed a slow decline. Naturally, people who slept eight hours each night performed best. The researchers found that sleep-deprived people normally cope with the condition through denial.

The research was published in the journal Sleep. While the study revealed what we already know – that not getting sufficient sleep is bad for the health – some experts expressed concern about the findings.

"There's nothing magical about number. Everyone has different sleep needs," said psychologist Joyce Walsleben from the New York University. Walsleben added that people will know if they're getting enough sleep if they don't feel like dozing off during a boring situation in the middle of the day.

The National Sleep Foundation said people have varying needs for sleep. These needs are governed by one's health and lifestyle.

To find out how much sleep you need, it's important to check where in the "sleep needs spectrum" you belong, which details the recommended hours of sleep needed depending on one's age. However, it's just as important as looking into the factors that affect sleep quantity and quality, such as work schedule, stress levels and environmental factors.

In a recent study, researchers found that light pollution at night affects both sleep quantity and quality. Researchers from California's Stanford University found that reduced exposure to darkness can mess up one's sleep patterns. Light sources from the neighborhood such as street lamps can make it harder for people to sleep at night.

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