Imagine a night water entry, a ready dive team, and your flashlight blinking twice before turning off just as you put your head under the surface. Does the dive end there, or does it continue with a single beam for two?
A dive light is chosen with a few simple questions: what is it for, how long does it last, how does it travel, and how do you keep it waterproof.
Our old page piled up promises (“next-generation LED,” “resistance to extreme conditions”) and told of a wreck revealed at 40 meters by 2000 lumens, without any source. We have redone everything. No model was tested for this article, and no brand is mentioned.
Main light or backup light: which one to take?
The main light illuminates your path and the reef. The backup light is used to finish the dive or to surface when the main one fails. For a night dive or in a dark place, logic dictates that you carry both, stored in different places on your gear.
The main light is often bigger, with a handle, a wrist strap, or a separate head connected to a battery pack. The backup fits in a pocket or clips onto a strap. It doesn’t need to be powerful. Above all, it must turn on reliably, even after months at the bottom of the bag, with batteries or a battery charged before departure. Check it on the boat.
During the day, a small light is also useful to look into a crevice or under an overhang.
But the real issue remains failure. A single light is a single point of failure, and the only serious solution is to double the light source rather than hope the battery lasts until the end. Ask the club what it requires for its night dives. Rules vary from one organization to another.
How many lumens and what beam angle?
Lumens measure the total amount of light emitted by the lamp, but they say nothing about the range or shape of the beam you will see underwater. A high number does not replace a suitable beam. There is no good lumen count valid for all waters worldwide.
The angle matters just as much. A narrow beam, called “spot,” concentrates the light and reaches farther. It is used to show something to your buddy, to search a hole, or to signal your position. A wide beam, called “flood,” illuminates a larger area but not as far. It is suitable for photography, video, or reading an instrument.
In water loaded with particles, a powerful wide beam reflects some of the light back to your eyes, like headlights in fog. You then see a white veil instead of the scenery. More lumens can make things worse.
In short, start from your water.
And beware of product sheets that announce lumens without saying how they were measured, or how long the lamp maintains that level before dimming. An adjustable mode, with a strong setting and an economical setting, lets you adapt the light to the day’s visibility.
Why do colors disappear with depth?
Water absorbs sunlight color by color, and red goes first. According to NOAA Ocean Exploration (page updated in 2020), red is quickly filtered as depth increases, and at 100 meters it no longer penetrates at all. A lamp restores these colors because it lights the subject up close.
This is why a goldfish appears gray or brown at a few tens of meters. Its color hasn’t changed. It’s just missing the red light to reveal it. NOAA also explains that many deep-sea red animals become almost invisible because of this filter. With your lamp at short distance, the light passes through little water and returns with its colors. The farther you move from the subject, the more the water takes over.
The exact depths where each color fades vary with water clarity.
Yet, precise thresholds are often read, down to the meter for each hue, presented as fixed rules. We do not repeat them here, lacking a source that holds for all waters.
Battery life, batteries, and airplane: what are the rules in 2026?
The announced battery life depends on the mode used: a lamp can last long in economy mode and much less at full power. For airplanes, IATA (2026 passenger document) sets the key limit at 100 Wh per lithium-ion battery, and spare batteries travel in the cabin only.
| Lithium-ion battery (IATA, 2026) | Spare in cabin | Spare in hold | Airline approval |
|---|---|---|---|
| Up to 100 Wh | Yes, maximum 20 per person | No | No |
| From 100 to 160 Wh | Yes, maximum 2 (have the count confirmed by your airline) | No | Yes |
| More than 160 Wh | No, transport as cargo | No | Not applicable |
Watt-hours are calculated by multiplying the voltage by the capacity in ampere-hours. Check the label. If nothing is marked, ask the manufacturer before going to the airport. Each spare battery must be individually protected against short circuits, either in its original packaging or with a piece of insulating tape on the terminals. A mounted lamp can go in the hold if it is completely off and protected against accidental activation.
Thus, the simplest is to keep the lamp and its batteries in your carry-on luggage.
The page from the Ministry in charge of transport on regulated items on planes (published in 2022) uses the same 100 Wh threshold and reminds that each airline may add its own restrictions. A battery used to charge another device counts as an external battery, limited to two per person in 2026 and never recharged on the plane’s outlets. Always check your airline’s page a few days before the flight, because these rules change from year to year.
How to use your lamp for night diving?
At night, your lamp is used to see, to be seen, and to communicate with your dive group. Check the two lamps on the boat, then review at the briefing the light signals learned during training. Aim in front of you, downwards.
A beam aimed into a diver’s eyes blinds them for a few seconds. The same beam on a sleeping animal can disturb it, and the instruction remains not to touch anything, as explained for the reasons to never touch marine life. The surface marker is a separate matter. To signal yourself to the boat during ascent, the dive parachute is combined with your lamp. The rest is arranged at the briefing.
Some parks also regulate light sources.
At Bonaire, STINAPA prohibits disposable chemical glow sticks, according to its rules consulted on October 3, 2026. If you prepare a shore dive at Bonaire and Lac Bay, plan a rechargeable electric marker instead of a glow stick, and note that dive gloves are also prohibited there except for medical exemption.
Waterproofing and maintenance: how to avoid a flooded lamp?
A lamp almost always floods due to a dirty, pinched, or dry O-ring. Before each dive, inspect the O-ring, remove grains of sand and hairs, then close without forcing. After the dive, rinse the lamp closed with fresh water, let it dry, and only open the housing once dry.
The IPX8 rating does not tell you how deep to go. This class of the IEC 60529 waterproofing standard designates immersion beyond one meter under conditions defined by the manufacturer, so the actual depth is found in the manual and nowhere else. Our previous version presented IPX8 as sufficient proof. We have corrected that.
The O-ring deserves two minutes each time.
However, lubrication is done with the product indicated by the manufacturer, in a thin layer, because excess grease attracts sand. Replace a cracked or flattened O-ring. Also keep a spare O-ring in your parts kit. For long storage, remove the battery and store it half-charged if the manual recommends it. A glance at the pressure gauge and the lamp during the dive prevents running out of air or light. The real cost of a neglected lamp? A canceled dive, sometimes a pair of batteries to replace.
FAQ
Is a lamp necessary for daytime diving?
Not necessarily. A small lamp helps to look into holes and under overhangs, and it brings out colors on a nearby subject. For night diving or in dark places, the main lamp and backup lamp become essential.
How many lumens are needed for night diving?
No single number applies to all waters. Lumens do not indicate the range or the beam angle. In murky water, a lamp that is too powerful and too wide can even reduce what you see.
Can a dive light be checked in luggage?
A mounted light can go in checked luggage if it is completely turned off and protected against accidental activation, according to IATA in 2026. Spare batteries remain in the cabin only. Also check your airline’s rules.
What does IPX8 mean on a lamp?
IPX8 means immersion beyond one meter under conditions set by the manufacturer. The rating does not specify a maximum depth. Read the depth specified in the manual.
Why do photos without a lamp appear blue?
Water first absorbs red, then other colors as light travels through more water. A lamp close to the subject restores these colors.
Sources
- Why are so many deep-sea animals red in color? (NOAA Ocean Exploration, updated 2020)
- IATA Guidance Document for Passengers Travelling with Lithium Batteries 2026 (IATA, 2026)
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