Night Diving Basics: Lights, Signals and Staying Together

What changes when the sun goes down

The water is the same. What changes is how much of it you see at once. PADI's description of a first night dive: "The first thing you'll notice is your vision narrowing to only what is lit by your flashlight." PADI adds that communicating with a buddy is a challenge, finding the entry and exit points is more involved, and staying with your buddy is much more critical at night. Our training guides cover where the night specialty sits.

The other change is how fast small jobs stack up. In a DAN case summary, three experienced divers were at about 20 m (65 ft) at night when one tried to loosen a weight belt he could not see past his BCD. The belt end came out of the buckle, leaving him holding belt and weights, floating up, and calling two buddies with his light from about 15 m (50 ft) behind them. DAN records that he became anxious and at the edge of panic before they saw the signals.

None of that needs darkness, apart from the part that matters: nobody can glance sideways and notice a buddy struggling. DAN's lessons include closer physical proximity at night, a contingency plan agreed beforehand, and practising new gear somewhere controlled. Our guide to panic and anxiety underwater covers the early signs.

Do you need a night diving certification?

No agency stops a certified diver going in after dark, and most sell a night specialty anyway. The common floor is an entry-level certification: SSI, SDI and NAUI all accept Open Water Diver or the equivalent. Past that they disagree, mostly about age and instructor ratio.

SSI sets the minimum age at 10 and allows 8 students per instructor. SDI sets 18, or 10 with parental consent, and caps open water at 4 students per instructor. NAUI wants 15 by the water phase of the course, with junior certification for ages 10-14. PADI's public course page describes the experience without listing prerequisites, so ask the dive centre.

BSAC treats night diving as a practice rather than a certificate, in the night diving section of its Safe Diving guide. Two of its lines are worth memorising: "You and your buddy should have a minimum of one working torch each at all times" and "If your torch breaks, and you don't have a spare, you should terminate the dive."

Primary light, backup light, beam angle and burn time

DAN's primary light should be "powerful enough to cut through the darkness and wide enough to provide a good field of vision", and "carrying at least one backup light on every night dive is advisable". On width DAN splits the job in two: "A narrow beam is ideal for looking into crevices and spotting distant objects, while a wide beam is better for general visibility."

Burn time belongs to a power level, not to the torch. Bigblue rates its AL1300NP at 2 hours on 1,300 lumens, 4 hours on 650, 8 on 325 and 20 on 130. Reading 20 hours off a box and planning a dive on it is how people end up in the dark.

If the primary dies, BSAC decides it for you: end the dive when you have no spare. SDI lists the required student equipment for its night course as "Lights; primary and back up" plus a whistle or audible signalling device, and it puts light failure in the same lesson as disorientation and lost buddy.

Night diving light signals, and how not to blind your buddy

Two signals cover most of a night dive. PADI teaches a large circular motion with the light for OK, and quick side-to-side horizontal movements for a problem. For anything more detailed, shine the beam on your own hand and make the standard hand signal inside it. SDI splits it by distance: hand signals when close, light signals further out.

The beam goes on your hand, the sand or the reef, never on a face. BSAC says avoid shining your torch in your buddy's eyes, and SDI lists "Don't shine light in buddy's eyes" next to night vision in its buddy contact lesson. Agree the set before you get in, because BSAC's point stands: complex hand signals do not work as well in the dark.

• OK, at a distance: one large circle with the beam (PADI).
• Problem: quick side-to-side horizontal sweeps (PADI).
• Anything more detailed: light your own hand and make the normal hand signal (PADI).
• On a buddy line, which SDI teaches for limited visibility: one pull stop, two pulls go or OK, four pulls surface, five or more come quick.
• On the surface: five or more whistle blasts means distress (SDI).

How close to stay, and how the exit gets marked

Closer than you think. SSI's advice for a new night diver is to stay within reaching distance. DAN's is to stay close and check in frequently. PADI asks buddies to agree the distance before descending, because poor visibility loses you a buddy over a much shorter gap than daylight does. The DAN case above puts a number on it from the other side: 15 m was already too far for a diver who needed help.

The exit gets lit before anyone gets in. DAN's boat setup is a light-emitting device affixed to the boat to identify it as the exit, chemlights on the anchor line, and a strobe on the bottom of the ladder to show divers below where the boat is. Off a beach the same logic needs a fixed shore light nobody can confuse with a car park.

For the surface, DAN says carry signalling devices that can be seen in the dark, and notes that some surface marker buoys are designed to take a light source, which lights up the whole tube. Our guide to deploying an SMB covers the deployment itself.

Planning the entry and navigating in the dark

Every agency gives the same first piece of advice, so take it seriously: dive a site you have already seen in daylight. BSAC says being familiar with the site helps with navigation and to explore it in daylight before night diving where possible, and DAN says the same. SSI suggests using the daylight dive to fix the landmarks you will steer by, such as rock formations and coral heads. Getting in at dusk rather than in full darkness gives your eyes a gradual handover, which SSI calls the perfect time to descend as a night diver.

Then the instruments. DAN recommends a reliable underwater compass, preferably one with glow-in-the-dark markers meant for night navigation. SDI's navigation lesson lists what you actually steer by: bottom contour, compass, the boat, the beach or lake shore, and a marker light or strobe. Its second course dive is a fair self-test later on, because it asks for a two-minute swim without a compass, then surfacing to reorient, then descending and navigating again.

Gas and depth planning: why the same dive costs more air

Because more of you is working. DAN's review of gas management incidents states that exertion, stress, anxiety and environmental factors can all increase respiratory rate, and that lobster hunting or spearfishing may use gas five to 10 times faster than usual. One of its cases is a night dive: the diver "introduced new environmental factors (a night dive in cold water) and new equipment (a drysuit), and he failed to make adjustments for any of it".

So plan on a higher surface air consumption than your logbook average. Our SAC calculator uses bar used times cylinder litres, divided by minutes, divided by average pressure in atmospheres; run it backwards for planned time. At 12 m (40 ft) the average pressure is 2.2 ATA, and a 12 L cylinder filled to 200 bar held to a 50 bar reserve gives 150 bar, or 1,800 L, of usable gas.

DAN also suggests building a gas limit into the plan, such as turning for the exit when the first diver has used a third or a half, reserve excluded. Depth is the other lever. SSI's position is that a night dive rarely needs to be deep and that shallow is better in poor visibility, because panic or separation has a shorter route to the surface.

• At a calm 13 L/min: 1,800 divided by (13 x 2.2) is 62 minutes.
• At 18 L/min, which cold water and task loading can produce: 1,800 divided by (18 x 2.2) is 45 minutes.
• A rise of 5 L/min costs 17 minutes of bottom time, before any reserve.

What you actually see after dark

Not the same animals asleep. NOAA Ocean Exploration describes diel vertical migration: billions of zooplankton, including small fish, shrimp and jellies, swim up to food-rich surface waters at night to feed when light is scarce and they are hidden from predators that hunt by sight, then return to the depths before sunrise. NOAA calls it the greatest migration on Earth. Some of the small life in your beam was hundreds of metres deeper at midday.

The feeding happens on the rock too. NOAA's corals tutorial states that most coral polyps feed at night, taking zooplankton and, where the polyps are large enough, small fish, caught with stinging cells called nematocysts in the tentacles. A coral head that looked like stone at noon has its tentacles out.

Bioluminescence is worth switching your light off for. NOAA notes that 80 percent of the animals living between 200 and 1,000 m produce light, usually blue because blue travels best through water. The sparks divers see in the shallows come from something smaller: a 2024 paper in Sensors reports that in coastal regions the main source of mechanically stimulated bioluminescence is dinoflagellates, roughly 15-100 micrometres across, responding to shear around moving objects, with most flashes lasting about 0.1-0.25 seconds. Cover the torch and wave a hand.

Mistakes that show up on first night dives

Most of them are decisions made on land, hours before the dive.

• One light. SDI requires "Lights; primary and back up" plus a whistle, and BSAC ends the dive when a torch breaks with no spare.
• Too many new things at once. A diver treated for a mild CNS bend after a deep night wreck dive told DAN there were "just too many new factors in this dive": a night dive, new gear, a camera and unfamiliar buddies.
• Unfamiliar kit in the dark. SSI's fix is to dive the same set-up in daylight first, so you find the octopus, gauges and inflator by feel.
• Letting the gap open. 15 m was enough to leave a diver signalling for help with a torch in DAN's weight belt case.
• The beam on faces. SSI adds that light in the eyes of sea life stresses the animals too.
• Silt. SSI notes that poor buoyancy kicks sand off the bottom, and at night you are the one lighting the cloud.
• Forgetting the surface. DAN says carry signals that can be seen in the dark, and SSI reminds you there is no sun waiting at the exit.

Pre-dive checklist for a night dive

This is your normal buddy check plus what darkness adds. Run the standard sequence first, using our buddy check guide for the order, then work through the rest while there is still light to see the kit by.

• Primary light tested at the level you will dive, not only on full power.
• Backup light tested, clipped where your other hand can reach it.
• A marker on you: strobe or glow stick on the BCD or valve (PADI).
• Compass, glow markers if it has them, and the daylight headings (DAN).
• Surface signal for the dark: an SMB that takes a light source, plus a whistle (DAN, SDI).
• Signals agreed out loud: OK, problem, turn, surface (BSAC).
• Buddy distance agreed, and what each of you does if the other disappears (PADI, DAN).
• Gas limit and maximum depth agreed, reserve excluded (DAN).
• Exit lit: light on the boat, chemlights on the anchor line, strobe at the ladder, or a fixed shore light (DAN).
• Dry clothes and something warm waiting at the exit (SSI).