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PHILADELPHIA (CBS) — The TV is off, the bedroom is cool, and you’re about to get a good night sleep but an important question still needs to be answered.  How many hours before that alarm starts buzzing?

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Neuroscientists from the Brain and Mind Institute at Canada’s Western University say that they’ve wrapped up what they’re touting as the world’s largest sleep study and found 7 to 8 hours of nightly rest is the perfect amount of sleep for almost any adult. No more, no less.

“That’s really surprising. I don’t think most people get that at all. We’re all too busy to get that amount of sleep in our day,” chimes in one viewer.

The study analyzed 40,000 people and found those who slept more than that magic range were impaired. They suffered short-term memory loss and had poorer reasoning skills.

Those who clocked in less than 4 hours a night performed in tests as if they were 9 years older than their actual ages.

“It takes about 90 minutes to go through one cycle so if you can do 3-4 cycles, that adds up to 7-8 hours,” explains Marc Johnson the clinical director at Drexel’s Sleep Center. He says the 7 to 8 range has to do with the number of restorative sleep cycles your body needs, which averages 4 per night.

And unfortunately, naps don’t count.

“Naps should only last 20-40 minutes at a time. Anything more than that you’re getting into sleep really,” explains Johnson.

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If you’re having trouble reaching that goal and counting sheep isn’t working — turn off the electronics.

Turning off the television and phone can make a big difference in falling asleep sooner rather than later.

Just simply focus on that deep doze and remember that you need to get that sleep.