One of my all-time favorite underwater experiences was a spur-of-the-moment night dive in Summersville Lake in West Virginia. We were diving off of a small boat at a place called Long Point, and the conditions were just right. The water was clear and the lake surface was flat calm. We were finishing a nice dive, exploring a very familiar site when we came to the flat rock where we would usually hang out during safety stops. We paused on the rock and looked up at the surface. The full moon was bright in the sky and we could see it clearly reflected on the surface of the water.

Instinctively, we all leaned back on the rock and watched our bubbles rise to the surface and enjoyed this unique view of the moon. I don't remember anything else about the dive, but that image of the night sky through the water will be locked in my memory forever.

I often tell people if I had to choose between day diving or night diving, I would probably dive exclusively at night--it is that much fun--but a surprising number of divers shy away from night diving out of fear or a belief that it's more trouble than it's worth. In reality, nothing could be further from the truth. Here are 10 night-diving tips that will help you stay safe and get the most fun out of your next after-hours excursion.

Stay close and shallow

Night diving is special because even a familiar site looks different at night. When you make a day dive, you normally scan the entire dive site looking at your surroundings. At night, you see only the area of the dive site that is lit by your light. This forces you to slow down and concentrate on that one area.

"When we take divers out for a night dive on our boats, I always tell them they don't need to travel far from the boat," says Spencer Slate, owner of Captain Slate's Atlantis Dive Center in Key Largo, Fla. "Your sight is limited to the beam of your lights. There is so much to see differently at night, you just don't need to go that far."

His advice: Find a coral head on the sand, park yourself on the bottom and systematically search the individual crevices and crannies for life. "Shine your light under ledges to see all the 'eyes'--lobster, shrimp and fish--that come out at night," Slate says.

Night dives tend to be shallow, so you'll have plenty of bottom time to go slow and take it all in. Colors, for example, are much more vivid on a night dive than they are during the day. It's simple dive physics. If you're making a daytime dive in 66 feet of water, sunlight gets absorbed, stealing away the colors. On a night dive, your light source is never more than five or 10 feet away, so the water doesn't take away any of the light spectrum.

Redefine "night"

When the sun is low in the sky, very little light penetrates the surface, making it pretty dark underwater even when there is still a fair amount of light above. Diving at dusk is a good way to start your night diving career. You have the convenience of gearing up when it is relatively light, but get the full effect of making a night dive. On ocean dusk dives, you also have the added benefit of watching the reef creatures migrate through a kind of "shift change" as the day animals disappear and the night animals come out to play (see "The Night Shift").

Get the right gear

You'll need a primary dive light and a backup light. The primary light should be the larger and brighter of the two. How large and how bright? That's up to you, and your choice may vary depending on the clarity of the water. When shopping for a light, try out several as some have different grips and handles to suit your personal preferences. (For details on 17 of the newest dive lights on the market, see our Scuba Lab Review)

Your backup--or pocket--light should be small enough to stow easily, yet bright enough to help you find your way back home. Most lights designed for this purpose are smaller and typically shaped more like a traditional flashlight. Remember, though, that if the primary light fails and you switch to your backup, it's time to end the dive.

Many divers also take glow stick marker lights or blinking strobe lights that they can attach to their dive gear. This allows the dive leader to find them easily, even when they are pointing their lights in the other direction or their dive lights go out.

Tie one on

Most dive lights come with a way to attach a lanyard or wrist strap. Get one. It's cheap insurance against dropping and losing your primary source of illumination. Most dive lights are negatively buoyant; if you drop one in deep water it may be gone forever.

Know the signals

If there's one aspect of night diving that is more complicated than day diving, it's communication. You and your buddy should review hand signals before entering the water and agree on the ones you'll use. You have two options: One is to shine the light on your hands so your buddy can see what you're saying. The other is to make signals using your light, explains Phil Graff, owner of Omni Divers and a dive instructor trainer in Washougal, Wash. "You can signal 'OK' and 'Yes' or 'No' by moving your light in a circle, or up and down, or side to side. You can even get your buddy's attention by circling or 'lassoing' his light beam and then pulling it toward you. If you've practiced this beforehand, your buddy will know what you're doing."

Should you become separated from your buddy, get vertical and shine your light outward while turning a full circle. Your buddy should do the same and chances are you'll spot each other. If you surface far from the dive boat, point your light at the boat until you get the crew's attention, then shine it down on your head so the crew can see you clearly.

Aim carefully

On any night dive, you should treat your light like a loaded gun. Never shine your light directly into another diver's eyes--you can ruin his night vision.

Go easy on the light

First-time night divers tend to buy the biggest, brightest beam they can find and cling to it like a security blanket. As you gain experience diving at night and get comfortable, you'll find smaller primary dive lights do just as well, particularly in clear water. On some night dives, lights of other divers, the boat and the moon can provide so much ambient light that you may leave your torch off for much of the dive.

If you do need a light, you may not need its full power. Some LEDs have a half-power setting you can use to dial back the brightness. Or try dimming your light by cupping your fingers over it. In any case, you'll see more natural behaviors if you use the edge of the pool of light, not the hot spot, to pick out fish and critters.

One of the unique things about night diving in the ocean is bioluminescence. Some varieties of single-celled plankton give off light when they are disturbed underwater. Your fin kicks or a wave of your hand can create an explosion of undersea sparks, but you'll miss the show in anything but dark conditions.

Do reconnaissance

Before you make your first night dive on a site, you should dive it during the day. This allows you to learn the layout of the site and get comfortable with it. "When I take students night diving, we always dive the same site earlier in the day. I point out certain features of interest," Graff says. "On the night dive I point out the same features so my students can see if they've changed or if their perception of them has changed."

Mark the way home

If you're diving from shore, rather than from a boat, you should also place lights on the beach. It's a good idea to have two lights close together at your entry/exit point and then a third farther away. This gives you something to swim for after the dive when you're swimming back in. "Have someone on shore monitor the shore lights," suggests Graff. "People will walk along the beach and see a light and take it with them, rather than realizing someone might be out in the water."

Making a night dive from a boat brings with it a different set of concerns. The boat should be marked with a flashing strobe you can use to find your way back. When surfacing near the boat, shine your light toward the surface and watch carefully to avoid colliding with the hull.

Have fun!

Most importantly, relax and enjoy the dive. It's natural to be a little anxious before stepping in the dark void of an unlit ocean or lake, but it's also exciting. When you overcome your anxieties about night diving, you get another eight hours of each precious dive day to explore and create new and lasting dive memories. Eric Douglas is the training director of Divers Alert Network (DAN) and the co-author of a new book, Scuba Diving Safety.

The Night Shift

According to the book The Coral Reef at Night by Joseph Levine, here’s what to expect on a Caribbean reef when the sun goes down.

At Dusk: Hunters from both daytime and nighttime shifts look for quick kills in the confusion. Reef sharks, for example, hug the reef so their prey is silhouetted against the twilit surface. As daytime fish settle in for the night, defenses go up. Triggerfish dive into crevices and erect dorsal spines to lock themselves in place. Parrotfish wrap themselves in a blanket of repellent mucus. Mating also takes place in the fading light. Surgeonfish, grouper and wrasse engage in "spawning rises," ejecting bursts of eggs and sperm into the water.

During Prime Time: In full darkness, corals and gorgonians expand their bodies and blossom with flower-like polyps and stinging tentacles, hoping to catch drifting plankton. Nudibranchs, unprotected by shells, come out to graze. Crabs, lobsters, brittle stars and urchins leave their holes to feed and mate. Octopuses and seahorses become more active.

After Midnight: As dawn approaches, the movie spools in reverse. Grunts and groupers return to their holes, while sleeping parrotfish begin to stir. Soft and hard corals wilt and retract as the light grows stronger. Twilight hunters assault the morning rush hour, but soon lose their edge over the daytime reef fish streaming from their cracks and caves. The familiar daytime population reappears and the cycle begins anew. --John Francis

September 2007