It's about 2 p.m. in Miramar, Fla. At the far end of a parking lot serving several office buildings, Jorge Hernandez opens the back door of his 2004 Honda Accord and disappears inside.

Twenty minutes later, he climbs out and heads back to his office, alert and ready to battle whatever the rest of the day has in store.

It's a ritual Hernandez follows religiously Monday through Friday.

"I don't know what I'd do without my daily power nap," he says.

Leonardo da Vinci, Albert Einstein and Thomas Edison -- all champion power nappers -- would have agreed. It could be argued that Edison was the first person to turn off the lights for the sole purpose of catching some midday Zs.

Research shows that a 20-minute nap in the afternoon may be just what the doctor ordered to recharge your battery and increase productivity for the rest of the day.

Long And Short Of Naps

The term "power nap" was originated by Dr. James B. Maas, author of "Power Sleep: The Revolutionary Program That Prepares Your Mind for Peak Performance." Maas defines a power nap as a short period of sleep that ends before deep, or slow-wave, sleep kicks in.

Dr. Sara Mednick, a researcher from the Salk Institute for Biological Studies, lists on her Web site improved heart function, hormonal maintenance and cell repair as some of the benefits of power napping. Her research also indicates that power naps can lift your moods, lower stress and improve memory and learning.

But in order to be effective, a power nap must not go on too long.

"I'm a nap junkie,"says Peter Castellanos, a sales and marketing consultant who credits naps for helping him stay focused during workdays that often go beyond 12 hours. "But if I'm asleep longer than 15 to 20 minutes, I get cranky and moody and am worthless the rest of the day."

That's what happens when someone goes beyond stages I and II of the sleep cycle, Maas said in his book. Sleep comes in five stages that repeat every 90 minutes throughout the night. Once you enter stage III, you are in slow-wave sleep and are entering deep sleep. Waking during this stage or later produces what's called sleep inertia.

Naps Don't Replace Long Sleep

While a 20-minute nap is a good refresher, it won't make up for hours lost at night.

Studies show that those if you lose sleep one night, your body makes up for it by increasing the amount of deep sleep you get the next night. But you can't catch up on sleep lost over a long period of time.

If you are often sleepy, or you find that your naps last longer than 30 minutes, it may be that you're not getting enough quality sleep at night.

Despite the benefits of a power nap, you still need an adequate amount of sleep every night to perform at your best, sa Maas. For some people, six hours might be adequate. Others may need eight hours or more. It's up to you to determine what amount is right for you.

The combination of quality nighttime sleep and consistent power naps will keep you alert and consistent throughout your waking hours.

"The return on investment of those 20 minutes a day is amazing," Castellanos says. "Power naps have added hours to my day by increasing the quality of the hours I'm awake."

Nap Tips

While there is no right or wrong way to take a nap, here are some tips for reaping the benefits of this midday ritual.

1. Try to schedule power naps after lunch. Experts say 2 or 3 p.m. is best. If you nap any later, you risk falling into slow-wave sleep or interfering with your regular night sleep.

2. Eat foods that are high in calcium and protein an hour or two before your nap. These foods help induce sleep. Avoid high-fat foods and foods that are high in sugar.

3. Use caffeine wisely. A Japanese study found that a cup of coffee 20 to 30 minutes before your nap may help avoid post-nap grogginess. It takes that long for your body to feel the effects of caffeine. The researchers concluded that by taking a power nap right after drinking a cup of coffee, you enjoy the benefits of the nap and wake up as the caffeine is kicking in.

4. Find a quiet place where you won't be disturbed. If you're not lucky enough to have a private office and a comfy couch, your parked car can work just as well. Remember to turn off your cell phone and, if you nap in your car, crack open a window.

5. Make the area as dark as possible. If necessary, wear an eyeshade. Darkness stimulates melatonin, a hormone that helps induce sleep.

6. Keep the temperature at a comfortable level. Body temperature drops when you fall asleep. Keep a light blanket handy just in case.

7. Relax. Turn off the to-do list in your mind and let yourself go.

8. Set an alarm. This insures you will wake before you enter deep sleep and won't miss an important meeting or appointment.

9. Be consistent. Experts suggest that working a 20-minute nap into your routine will help your body expect it. The more naps become part of your routine, the more you will reap the benefits.

10. Get rid of guilt. Researchers agree that power naps are great for your health and productivity. Taking a nap doesn't mean you're being lazy. So, stop feeling guilty.

Tips based on information from RirianProject.com and Powersleep.org.