SeaLife Sea Dragon Mini 900S

Lumens measure the total light output, but they say nothing about how that light is shaped, so a tight narrow beam can look far brighter at distance than a higher-lumen wide beam. Beam angle, color temperature, and water clarity affect what you actually see as much as the lumen figure does. Use lumens to compare lights of a similar beam type rather than as a single score of quality.

A primary light is your main light, usually brighter, larger, and with a longer burn time, while a backup is a small, simple light carried in case the primary fails. Any dive where you need a light to exit safely, such as a night dive, calls for carrying at least one backup. Backups are chosen for reliability and simplicity rather than for maximum output.

Burn time and brightness trade directly against each other, so the same battery run at a lower power setting lasts substantially longer. Manufacturers usually quote burn time at each power level, and many lights automatically step down output as the battery drains or the head heats up. Treat quoted figures as fresh-battery, ideal-condition numbers and plan for more burn time than your dive actually needs.

The o-rings sealing the battery compartment are what keep the light from flooding, so inspect them for grit, hair, and nicks every time you open it, and wipe the sealing surfaces clean. Lubricate lightly with the grease type the manufacturer specifies, using a thin film rather than a heavy coat, because excess grease attracts sand. Replace o-rings when they look flattened, cracked, or dry, and do not over-tighten the cap in the hope of sealing a bad o-ring.

Lithium batteries are subject to airline and regulatory limits that vary by cell chemistry, watt-hour rating, and whether the cells are installed or loose. As a general rule lithium cells travel in carry-on baggage rather than checked baggage, with terminals protected against short circuit, but you must confirm your airline's current policy and any local rules before you fly. Carrying the manufacturer's battery specification sheet helps if you are questioned at screening.

Rinse it in fresh water after each dive day and work the switch while it is submerged so salt does not crystallize inside it, then dry it before opening. For storage, remove or charge the batteries as the manual directs, and leave the cap loose so the o-ring does not take a permanent set. Never store a light with corroded or leaking cells inside it.

Test it briefly as part of your pre-dive check, but do not leave a powerful light running in air, because many are designed to shed heat into the water and can overheat on the surface. Check the manual, as some lights have thermal protection that dims or shuts them down when they are dry. Testing before you gear up is far better than discovering a dead light at depth.

No, batteries are not included. It runs on either two CR123 lithium single-use batteries or one 18650 Li-ion rechargeable battery, and you choose which power source to buy separately based on dive style and desired runtime.

Yes, using the optional SL98104 YS Mount accessory, which adapts this light to any male YS Adapter or YS Mounting system. This lets you attach it to a camera or video tray instead of carrying it as a handheld or BCD-clipped light.

Use a button-top (not flat-top) 18650 cell with integrated protected circuitry, a minimum of 2600 mAh capacity, a minimum 3.5A discharge current, and cells made by Panasonic, Sanyo Japan, or Samsung Korea. Do not use rechargeable CR123 batteries, as their voltage and amperage specs can damage the battery or the light.

It outputs 900 lumens at full power through a narrow 14 degree spot beam (10.5 degree underwater), which concentrates light for long-range viewing and pointing out sea life rather than wide-area flood lighting. Half power delivers 450 lumens and quarter power delivers 225 lumens, with color temperature between 6000 and 7000K.