Comparison Bailong Police BL-Q2888-T6 vs Bailong Police BL-Q2800-T6

General type of flashlight.

Hand lamps for general use are divided into full-size and compact. However, in addition to this, on the market you can find many models with a narrower specialization and/or specific design and mounting features: headlamps ; touring devices, including self-contained dynamo lights, L-shaped lights, and diving models; powerful hand lamps and ultra-compact key chains ; auxiliary lighting systems ; as well as underbarrel models and baton flashlights widely used in law enforcement agencies. It should be noted that one model can belong to several types at once. For example, most underbarrel flashlights are equipped with a removable mount for mounting on a weapon, and without such a mount they turn into hand-held or hand-held compact ones; and L-shaped models, in principle, are not an independent type of flashlights — most often this is a design feature of hand-held compact or head-mounted devices (or even models that combine both of these applications).

— Manual. Full-size hand-held flashlights over 20 cm long and weighing over 200 g represent a kin...d of "middle class". They are designed for those for whom compactness does not play a decisive role and functionality is important first of all. Such lights can carry on board more than 1 LED and powerful power supplies, providing a good luminous flux; they are often supplied with various additional functions.

— Manual compact. This type of flashlight is somewhat larger than key fobs, but can still be classified as compact devices: hand-held compacts look like a tube up to 20 cm long and weighing up to 200 g. They rarely install more than one LED, but their dimensions and weight already allow the use of fairly powerful sources supply, which has a positive effect on the characteristics of the luminous flux (see "Maximum luminous flux"). In addition, a number of additional functions can be used in this type of flashlight, such as focus and brightness adjustment (see below).

— Lantern on the forehead. Flashlights designed to be mounted on the head — usually with special elastic straps that can be adjusted to fit. Mounting features impose restrictions on the weight and dimensions of the lantern, which affects the functionality. When purchasing such a flashlight, it is worth considering that high brightness in this case may be a disadvantage — if you need light to work with objects in close proximity, excessive brightness quickly tyres your eyes. In this case, it may make sense to pay attention to models with brightness control (see below for more details). Typically, such models have the ability to adjust the angle of the beam, but the possibility (and features) of such adjustment needs to be specified separately.

— L-shaped. Lanterns in which the beam of light is directed perpendicular to the body; the body itself, usually, has a cylindrical or close to it shape. Most of these models, according to the main format, belong to hand-held compact ones, and many also allow use in the headlamp format (see above for both). Anyway, L-shaped lanterns with the possibility of manual use have a characteristic clip on the body — on the opposite side of the lamp. Such a clip allows you to hang the device on a belt, the edge of a pocket, an element of an unloading vest or other overalls, etc.; in this case, the light beam will be directed forward, the vertical position of the case will ensure the stability of the device, and the user's hands will be free. (Note that the first L-shaped lanterns designed for such wearing appeared as an element of army equipment — back in World War II, the US military fully appreciated the merits of such a design).
As for the forehead installation, in such cases the body is placed horizontally, and its mount is made movable. Turning the lantern in such a mount, you can set almost any angle of the beam; at the same time, regardless of this angle, the position of the lantern remains equally stable (whereas in some headrests with “heads” of an inclined design, such a “head” may tend to roll forward as the mount wears out).

— Manual lamp. The most powerful type of hand lamps, which can even be called "hand spotlights". Most of these devices are designed to give out a long-range and at the same time sufficiently thick beam of light — much wider than in many other types of lanterns. Actually, the illumination range of hand-held lamps often exceeds 100 or even 200 m, while the large beam width makes it possible to very effectively detect individual objects even at such large distances. Another, less common type of such devices are models that have a short range, but are capable of illuminating a vast area.
Anyway, flashlights of this type turn out to be quite large and heavy, so initially they are not designed to be constantly carried with you (although even one and a half to two hours with such a device in your hands usually do not cause much discomfort). It is worth paying attention to hand lamps in cases where the effective detection range (or bright illumination of a vast area) is of the most fundamental importance to you. In particular, such devices are very popular in rescue services: a powerful beam of a "portable searchlight" is indispensable for search operations at night. Also among the lamps of this type there are so-called "inspection" models, well suited for inspecting machines, industrial equipment, communications (cables, pipelines), etc.

— Tourist. Tourist lamps are mainly lanterns that were originally intended for organizing lighting in a camp, at a halt, etc. Such devices provide diffused light with a coverage of 360 ° horizontally and most often allow installation directly on the ground. In addition, most of them have a hook for hanging, sometimes supplemented with a built-in magnet (see below for both). Thus, such a lantern can be mounted on a tree branch, under the ceiling of a tent / awning, etc., significantly expanding the area of illumination — or hung on a backpack or other equipment, illuminating the path for several people at once.
Most tourist lanterns have only this specialization; however, there are also models that allow other applications. Usually these are hand-held compact devices of a special design — with a retractable diffuser made of white matte material. Such a device allows you to turn the directional beam into diffused light with full horizontal coverage; and when such a beam is not needed, the diffuser can be hidden in the housing. However, some of the more traditional travel models also have a folding design — it makes it easier to carry after hours, especially if the device needs to be hidden in a backpack or bag with other things.

— Dynamo flashlight. Lanterns equipped with a built-in generator (dynamo) that generates energy due to the user's muscular strength — usually for this you have to swing or twist a special lever. Thus, it is possible to recharge the built-in battery even in the absence of power sources (and such lights most often work from batteries). Such features are especially relevant for those who often have to be "far from civilization": tourists, military, researchers, etc. At the same time, dynamo lights can have different specializations — compact, tourist, etc.

— For diving. Lanterns originally designed for diving and long stays at great depths — usually from 50 m or more. Such models, by definition, have a sealed waterproof housing (see "Dust and water protection"). In addition, diving lights are often designed with specific features designed to provide additional convenience and safety. For example, the body can have bright colours or additional inserts that increase visibility under water, as well as be made of lightweight material so that the flashlight released from the hand floats to the surface and does not sink. Often, the device is supplemented with a carabiner for attaching to equipment or a hand strap (see "Complete set"). It is because of these additional features that not every flashlight with a high level of water protection is considered diving. Therefore, it is worth looking for a lamp specifically for diving among the models of this category.

— Auxiliary lighting. Lanterns designed to organize additional stationary lighting where there is no light or it is not enough. In a sense, such models are similar to tourist camping ones (see above), they can also be used in a parking lot or in a tent. However, the matter is not limited to this: many auxiliary lamps are originally designed for use in workshops, garages, etc. Some of them can also be hung on the open hood of a car, which can be very important for field repairs. But such models are not designed for carrying in hands: it is technically possible, but not very convenient.

— Trinket. This category includes the most compact models: their weight, usually, does not exceed 50 g, and the length is 10 cm. Hence the name — most of these lanterns can be worn instead of a keychain on a keychain. Actually, the convenience of wearing is the main advantage of key rings: you can always have such a flashlight at hand. The main disadvantage is low power: key fobs are usually equipped with one LED (see "Number of diodes"), and any "solid" power source in a compact case will not fit. At the same time, such lamps are quite enough for simple everyday tasks — for example, to illuminate the road on an unlit section of the street or find a keyhole if a light bulb has burned out in the entrance.

— Underbarrel. Flashlights designed to be mounted on a weapon are most often under the barrel, but installation on the side is also technically acceptable. Many of these models are essentially hand-held compact flashlights (see above), supplemented by a removable weapon mount (or the ability to install on such a mount — see "Packaging"), as well as, in most cases, a remote button (see below) ; however, there are also purely underbarrel models in which the mount is not removed. In both cases, the mount is usually designed for a standard Weaver / Picatinny rail, but this point needs to be specified separately. This also applies to the possibility of full-fledged use with firearms: the fact is that some underbarrel lights are intended for airsoft drives and are simply not designed for powerful recoil.

— Lantern-baton. Lanterns with a baton or baseball bat body and are strong enough to strike. Such a flashlight can be a very useful addition to the equipment of a watchman or law enforcement officer. Note that some so-called patrol lights, hand-held lights in a large and durable body of traditional design, also allow the use as a “percussion tool”. However, for them, such an application is an extreme case, while baton lamps are initially created as reliable and impact resistant as possible. Therefore, patrol models in our catalog are still not assigned to this category, but to ordinary hand lamps.

The maximum luminous flux provided by the lantern.

Luminous flux (denoted in lumens) can be described as the total amount of light produced by an LED or other light source and distributed in all directions where this source shines by itself (without lenses, reflectors, etc.). In fact, this means that the capabilities of the flashlight depend not only on the luminous flux, but also on the angle of illumination (see "Angle of illumination (light)"). For example, a relatively weak stream can be concentrated into a narrow beam, providing good range; and a large number of lumens will inevitably be needed to effectively cover a wide area.

Note that the coverage angle is not always specified in the characteristics, and even with such data it is difficult to immediately assess the real capabilities of the flashlight. Therefore, for such an assessment, it is best to use information about the actual illumination range (see below), and also take into account the general type of device (see above). For example, for the same number of lumens, a handheld flashlight with a reflector to form a directional beam will give a noticeably greater range than a tourist lamp with 360 ° coverage.

It should also be borne in mind that the high brightness of the flashlight is far from always justified, and it is worth choosing according to this parameter, taking into account the actual conditions of use. S...o, when working at short ranges, bright light can become a hindrance: it tyres the eyes and can blind others. In addition, an increase in brightness usually requires more powerful sources of both light and power, and the weight and dimensions of the lantern increase accordingly.

The maximum range at which the flashlight provides any effective illumination of objects. Different manufacturers have different criteria for this efficiency when measuring ranges, and therefore it is only possible to unequivocally compare among themselves in range only models of one manufacturer. At the same time, this parameter allows us to compare models from different manufacturers with some certainty: for example, flashlights with a lighting range of 15 m and 100 m will clearly belong to different range classes, regardless of manufacturers.

Note that the range of illumination depends not only on the maximum luminous flux provided by the lantern (see above), but also on the features of its design: the narrower the beam is provided by the reflector of the lantern, the greater the range will be, and vice versa — scattered light does not spread far. Some models allow you to adjust the beam width depending on the requirements of the situation (for more details, see "Adjusting the focus").

It is also worth bearing in mind that models with the same claimed lighting range can cover different spaces. For example, a hand lamp (see Type) with a reflector diameter of 20 cm will be able to provide a wider beam than a conventional hand lamp with a 5 cm reflector. And although in both cases the objects that fall into the light spot will be illuminated in the same way, however, in the first case, the size of the spot itself will be larger, and the actual efficien...cy of the flashlight will be correspondingly higher (in light of the fact that it is easier to "feel" individual objects with a wide beam, especially at a considerable distance).

Maximum runtime of the flashlight without changing batteries or recharging the battery.

Note that in models with brightness control, this time is indicated for the most modest and, accordingly, economical mode. For example, in a flashlight with a maximum luminous flux of 1000 lm, the claimed operating time of 20 hours can be achieved at a brightness of only 30 lm, and at maximum battery life may not exceed half an hour. These nuances should be clarified according to the detailed characteristics. However, also note that additional modes of operation (see below) are not taken into account in this case: for example, if the flashlight from our example in SOS mode can operate for 30 hours, the characteristics will still state 20 hours.

It is also worth bearing in mind that for models with replaceable batteries, the actual operating time will also depend on the quality of such batteries. For example, for flashlights for AA and AAA elements, battery life is most often given when using high-quality alkaline batteries; if instead of them inexpensive saline ones are used, the operating time may be several times shorter.

In general, when choosing a flashlight according to the maximum operating time, it does not always make sense to focus on “long-playing” models: they often have either low power or impressive weight / dimensions, and the price can significantly “bite”. Flashlights with a long battery life will be useful first of all to those who have to s...tay “away from civilization” for a long time: extreme tourists, rescuers, military, etc. And for most everyday tasks in a modern city, and even for trips to nature for several days, up to 10 hours is enough.

The number and types of additional modes of operation provided for in the flashlight.

Additional modes include all modes in which the flashlight operation format differs from the standard “constant luminous flux in the visible range without pronounced coloration”. Namely strobe, SOS, beacon, flicker, light, low / high beam, infrared (IR), ultraviolet (UV), red light, blue light, green light, etc. More details about each:

- Stroboscope. Fast flashing mode - several flashes per second. One of the most popular applications of this function is disorientation of the enemy in an extreme situation; in light of this, a stroboscope is often provided in underbarrel flashlights (see "Type"), as well as manual models of "tactical" specialization. In addition, fast blinking is well suited to distinguish yourself on the road - especially in cloudy weather or at night: such a light is much more visible than constant light, including with peripheral vision. At the same time, we note that when using a stroboscope, some caution should be observed: due to the specific effect on the p...syche, this mode can provoke exacerbations of certain diseases - for example, seizures in patients with epilepsy.

— S.O.S. The mode of operation is "three short flashes - three long - three short", which corresponds to the international signal "please help" (letters SOS in Morse code format). This eliminates the need to send such a signal manually and allows you to leave the flashlight to work autonomously, and take care of more pressing problems (which often accompany situations that require the "SOS").

— Low / high beam. Possibility to switch between far directional beam and near diffused light. This switching is most often accomplished by using multiple sets of LEDs; at the same time, in some models, each of these sets is responsible for its own mode, in others, all diodes work in the high beam, and only a part of them work in the low beam.

— Infrared (IR). Illumination in the invisible infrared range. It is used, in particular, to improve the efficiency of night vision devices and IR sights. Note that many of the LEDs responsible for this mode also glow in the visible range (red light) during operation; however, this glow is quite weak and, as a rule, is noticeable to the human eye only when looking directly at its source from a short distance.

- Ultraviolet (UV). Illumination in the ultraviolet range is mainly used to identify objects and traces that are invisible under normal lighting. One of the most popular ways to use this feature is with a makeshift currency detector: most modern banknotes have markings that glow under UV light. Also, such light can be used to detect inscriptions with “invisible” ink (including marks on the same banknotes), some biological (for example, blood) and chemical liquids (in particular, UV-sensitive compounds can detect leaks in pipes and liquid contours), etc. Note that the UV emitter usually glows in the visible range - with a characteristic bluish tint; this allows you to accurately determine whether such a light is on or off.

- Red light. One of the more popular complementary colors in modern flashlights; can be used both in combination with blue and green (in the so-called RGB models), and as the only auxiliary shade. One of the features of red light is that it practically does not affect night vision, does not penetrate through the eyelids, and even after complete darkness does not blind the eyes. This makes such lighting the best option, for example, for clarifying map data during a night hike, when you need to quickly restore vision after turning off the light, or for emergency lighting in a sleeping room, where you need to see the environment and at the same time it is undesirable to disturb sleeping people with the light. . Another way to use red light is signaling: this light travels farther than blue or green, and stands out prominently against most landscapes and man-made objects. Hue change can be carried out both due to the light filter on the main light source, and due to a separate LED.

- Blue light. One of the shades used in the main three-color "RGB-lanterns" - along with red (see above) and green. This light is intended mainly for situations where you need to effectively illuminate the space in front of you, but it is undesirable to use ordinary white light. Human vision is most sensitive just to blue and green shades; therefore, a relatively weak blue light flux allows a large amount of detail to be revealed. And in some situations, such lighting can be even more effective than white. For example, if at night a white lantern is pointed at a light object, then the space behind this object will be hardly noticeable due to the bright reflected light; and a weak blue light will evenly highlight both the "foreground" and the "background". But using this shade at high brightness, on the contrary, is undesirable - reflection from bright blue light will dazzle even more than from white, and even more so red. And if a blue beam, even a weak one, hits directly into the eyes, it will instantly knock out night vision, and it will take quite a long time to restore it.
Note that the choice between blue and the similar green (see below) depends on the specific situation: different shades may be optimal in different situations.

- Green light. Hue, most commonly used in tri-color RGB lights, but sometimes used as the only complementary color. In many ways it is similar to the blue described above - in particular, in some situations, a weak green light can clearly reveal details that are invisible in other shades (even under the same blue light), but high brightness is undesirable for such a beam. In addition, this color has its own specific feature: many animals almost do not react to green light, so it is especially convenient for hunting.

- Lighthouse. The mode of infrequent flashes with a repeating amplitude, most often at a relatively low brightness (with some exceptions to the rule). In some models of lanterns, you can even meet more than one version of the lighthouse. The mode is designed to detect and observe the user at a distance; at the same time, the beacon not only consumes battery power more economically than a constant light of the same brightness, but is also better visible from afar. We also note that in headlamps, the flicker mode performs a similar function (see below).

- Flicker. In this mode, the flashlight emits short pulses or shines with a variable, "pulsating" brightness. This format of work is not intended to illuminate the surrounding area, but to make the user more visible to others: a person reacts to flickering light reflexively, even if its source is far in the peripheral vision zone. The flicker mode will be useful primarily on the roads - for example, when walking or cycling at night: in the same city, such a warning for surrounding drivers will not be out of place, and there is no need to talk about dark country roads.

— Red blinking (red blinking, red beacon). This mode allows you to make the flashlight as noticeable as possible: the red light, especially the flashing one, catches the eye even in the daytime. And in the dark, this shade is also useful due to the fact that it does not harm night vision (for more on this, see "Red Light" above). But the specific specialization of the red flashing may be different, depending on the specialization of the flashlight. For example, in tourist models (see "Type"), this mode allows you to give a signal, indicate the location of the camp, collection points, etc.; and in headbands, it is used to highlight the user on the road and make him as visible as possible to others (primarily for car drivers).

- Lamp. The function is found, as a rule, among hand lamps and in tourist models of flashlights (as an addition to the main directional light). In fact, we are talking about a scattered light mode - as opposed to a directional beam that provides the main light source with a reflector. Diffused light does not differ in range, but it allows you to cover a significant space - for example, to illuminate an entire room.

- LCU. Laser pointer mode: the flashlight emits a laser beam, the mark from which points to the intended point of impact. It makes sense to provide for such a regime only in underbarrel models (see "Type").

Note that this list is not exhaustive: modern flashlights may provide for other, more specific modes of operation. In such cases, the features of the functionality should be clarified according to the manufacturer's documentation.

- Flashlight charger. A device for charging batteries directly in the flashlight. Note that models with both non-removable and removable batteries can be equipped with such a “charger”. In any case, such devices are extremely easy to use: you do not need to remove the batteries and put them in a separate device, just connect the flashlight to an outlet, auto outlet or USB port (memory devices can use different power sources, this should be specified separately). In addition, some flashlights with this function are able to work even while the battery is charging (in fact, from the mains). At the same time, chargers of this type are not as universal as "chargers" for individual batteries (see the corresponding paragraph).

- Car memory. The presence in the kit of a device for charging a flashlight from a car cigarette lighter (or a standard auto socket of the same size). Typically, such a device has the form of a simple plug with a cable; the cable can be made detachable. And in some models, a separate car charger is completely absent: to charge the battery, the flashlight itself is inserted into the cigarette lighter socket, and the body of the device plays the role of a plug. See "Power - Cigarette Lighter" for details.

- USB cable for charging. The presence in the kit is separately only a cable for charging, but without a...complete plug into an outlet. At the same time, you have the possibility to charge, for example, from Power-bank.

- Battery charger. A device for charging the batteries supplied with the flashlight. Only models with removable batteries are equipped with such a device - in fact, the battery must be removed to charge. This may create some inconvenience. On the other hand, batteries are usually made in a standard size, which gives many additional options. For example, you can buy a spare set of batteries and use it while the main one is charging, or even put disposable batteries instead of "native" batteries; The charger can be used not only for flashlight batteries, but also for other compatible batteries.

— Power element(s). A battery is included with the flashlight. This feature allows you to use the flashlight immediately after purchase, without buying additional batteries separately. Note that the presence or absence of a battery in the kit does not depend on the type of battery itself (see "Power"): for example, models for the original battery are not always equipped with such a battery. Therefore, if readiness for work “out of the box” is critical, you should choose a flashlight for which the battery is directly declared in the kit. At the same time, it does not hurt to clarify which element the product is equipped with - a disposable battery or a rechargeable battery.

- Light filters. Removable filters, commonly used to color the beam of a flashlight in one color or another - red, blue and / or green. See "Additional Modes" for more information on such colored lighting; Here we note two points. Firstly, the set of light filters can be different: for example, red light is common, but green and blue are much less common. At the same time, for some lamps, additional light filters are produced separately, they can be purchased in addition if necessary. Secondly, if a flashlight with colored light does not have filters in the kit, it means that this model uses separate colored diodes or, much less often, built-in filters. Both the one and the other option turns out to be more convenient from the point of view that to switch colors you do not need to mess around with interchangeable accessories (which you can forget somewhere or lose). On the other hand, additional equipment somewhat complicates and increases the cost of the design of the entire device.

— Clip for carrying. The presence in the design of the flashlight of a special clip (clips) - similar to that used in portable players, ballpoint pens, etc. This clip allows you to fix the flashlight on clothing, for example, on the edge of a pocket. This function is intended primarily for ease of wearing: a flashlight fixed with a clip will always be in one place, without getting lost or confused in your pocket.

- Bicycle mount. Fastening for installation of a lantern on a handlebar of a bicycle. Allows you to use the lighting device as a source of head light and indicates the presence of a cyclist on the road at night. As a rule, the holder is fixed on the steering wheel by means of a screw clamp, and the flashlight is held in it due to the elasticity of the mount.

- Strap. The presence in the design of the lantern strap for mount on the hand. It protects the device from falling: even if you accidentally open your fingers, the strap will hold the flashlight on your hand (or at least delay the fall so that you have time to react). And in diving models (see "Type"), such a device can, on the contrary, keep the flashlight from floating up. In large-sized hand-held lamps, the strap may be designed for ease of carrying on the shoulder, but such options are quite rare.

— Case. Existence in a set of delivery of a special cover for storage and transportation of a lamp. Such a case protects the device from excessive contamination and provides some degree of protection against damage. In addition, it can come in handy for protecting surrounding fragile items - for example, if you have to transport them along with a flashlight in a tightly packed bag or backpack.

- Underbarrel mount. Attachment for mounting an underbarrel flashlight (see "Type") on a weapon. Most often, such a mount is designed for a standard Picatinny / Weaver rail, but other options are possible; This point does not hurt to clarify before buying. In any case, this equipment is convenient because the mount does not need to be looked for separately; on the other hand, it may not be suitable for non-standard "seats".

- Without mount. The absence of a mount on a weapon in the delivery set of an underbarrel flashlight (see "Type"). Such models were originally intended for use for a different purpose - usually as hand-held compact ones (see ibid.), and the possibility of installation under the barrel is provided as an option. Also, you should pay attention to this option if the weapon has a non-standard way of installing flashlights - the mount for such an installation is easiest to buy separately from the flashlight.

On / off button, placed outside the body of the lamp and connected to it with a wire. A similar button is found exclusively in underbarrel flashlights (see "Type"): when installed on a weapon, it is attached under the shooter's hand, which allows you to turn the light on and off without removing your hands from the weapon and without changing your grip. At the same time, some models with this function are turned on and off only by a remote button, in others it is provided in addition to the switch on the case. At the same time, some models with this function are turned on and off only by a remote button, in others it is provided in addition to the switch on the case, and in others it is possible to replace a conventional switch with a separate button and vice versa.

Additional resistance of the flashlight to various kinds of shocks and shocks. The specific degree of shock protection for different models varies, sometimes quite noticeably; This point should be clarified according to the official documentation. At the same time, the vast majority of shock-resistant models are able to transfer at least a fall from their hands onto a hard surface without consequences, and anyway they are more durable than unprotected flashlights.

It is recommended to specially select a shock-resistant model, first of all, if your activity involves a corresponding risk — for example, extreme tourism, speleology, military affairs, security activities.

This feature is indicated for flashlights whose housings have an increased degree of dust and moisture protection. The degree of such protection may vary: for example, some models can easily withstand heavy rain, others “survive” being caught in a sea wave, and the most advanced ones can even be used when diving with scuba diving (see “Type - For diving ”). The features of protection should be clarified in each case separately; however, if you need a flashlight that can withstand adverse conditions, you should definitely look for it among the models that explicitly state dust and moisture protection. Such models will be useful primarily for those who often have to work in difficult environments: climbers and other “extreme” tourists, rescuers, military personnel, sailors, etc.

The level of protection is indicated by two numbers according to the IP standard ( IP65, IP66, IP67...). The first number corresponds to dust protection (maximum 6). The second number indicates the degree of protection from water; here in protected models, level 7 (the ability to immerse under water to a depth of 1 m for half an hour) or 8 (the ability to work for long periods of time under water at a depth of more than 1 m) is usually found. Thus, the maximum degree of protection according to this standard is IP68, completely sealed. There is also a marking like IPX8, where the first digit is not indicated - this only means that the flashlight has not been officially certified for dust resistance. In the above example, this is not necessary - water resistance 8 automatically means a sealed case, impenetrable to dust.

It is worth considering that even completely sealed models may have different restrictions on the maximum immersion depth. So if you are going to intensively use the flashlight underwater, you should make sure that it can withstand diving to the planned depth.