ABOUT DIVE TORCHES AND LIGHTS
Our Advice: Primary = LED canister light with rechargeable battery pack; Backup = 2x LED backups with non-rechargeable lithium ion batteries.
With so many different lights to choose from, both in type and technology, it is a confusing area for divers to make an informed decision. Let’s help by clarifying a few terms and technologies, then looking at a few things to consider.
Primary light – the light you use as your main light. Usually a canister type with separate light head and battery canister with a Goodman handle to slip over your fingers, keeping your hands free. May be either LED or HID.
Backup light – a secondary light carried for emergency use (such as a primary light failure), stored on the harness or in a pocket and not used unless necessary. Will be LED for longer battery life.
Note: Recreational divers will use a backup light as their primary light and eventually move it to the secondary position as they progress into more advanced diving.
Pistol grip light – a recreational design featuring a pistol style grip suitable for early single tank diving. Often the first light we buy and usually fails or floods due to cheap plastic manufacture. Will be LED.
Video light – a light with wide beam spread for video, equipped for mounting on underwater camera arms. May be either LED or HID.
HID (High Intensity Discharge) – The light source is a xenon globe, which is contained in a glass tube with a stainless steel reflector located behind the light source. This allows the focus point to be altered from a very tight spot to a wider beam by the diver as needed on the dive. There is virtually no loss of light energy. HID is a fully matured technology and further development is unlikely.
LED (Light Emitting Diode) - A newer technology where the light is produced on an electronic circuit board with optics placed forward of the light source. There is a loss of some of the light energy as it passes through the optics, which are often made from acrylic plastics. LED light optics are more difficult to use to achieve tight focus and the beam does not project as far as HID. LED is an ever evolving technology and 1000 lumens from one company may be equivalent to 1500 lumens from another. This all depends on how it is measured and also at what distance.
Note: Some LED manufacturers achieve apparently high lumens by stacking multiple LED globes in parallel, however, the distance projection, focus, and intensity of 5x 200 lumens LED is not by any stretch of the imagination equivalent to 1x 1000 lumens LED. High quality electronics beat quantity every time.
Rechargeable packs – best for primary lights because you use them every day and charge them overnight. May be recharged in the light itself (preferred) on an external recharging device.
Rechargeable batteries – individual NiHM or Lithium batteries capable of being recharged using an external recharging device. These do not retain their charge well over time.
Non-rechargeable batteries – individual single use alkaline or lithium batteries. Non-rechargeable batteries are not suitable for regular use due to waste and expense. For example it is wasteful and expensive to replace 8x C batteries in a pistol grip light after every 20 hours of use. However, non-rechargeable batteries retain their charge over time and are the best option for backup light and spares kit batteries that you do not intend to use unless necessary.
Rechargeable battery technologies
NiMH (Nickle Metal Hydride) – long battery lifespan (typically 1000 charge cycles) and easy to travel with in carry on or checked luggage.
LiPo (Lithium Polymer and other variants) – compact and powerful with a medium battery lifespan (typically 500 charge cycles). Must be put in checked luggage in most countries.
Midday sun = 5500-6000 Kelvin (Kelvin is the measure of light colour temperature).
21-watt HID = 6500-7000 Kelvin.
LED = 5000-6500 Kelvin.
A higher Kelvin rating is better for underwater use, as lower numbers have a higher content of the red light wavelength, which is absorbed by the water sooner than the bluer light wavelengths. This is one of the reasons HID lights tend to penetrate further than LED lights.
Brightness in watts and lumens
Watts are a measure of power and lumens are a measure of light on a surface (typically at 1 metre).
21-watts HID = 1450 lumens
(Note: Not the typical measure of brightness for HID but shown for comparative purposes.)
21-watts LED = 1100 lumens at a 12 degree beam focus
Many LED lights boast much higher outputs than this, but it all comes down to how tight the beam focus is and how much light is lost in the optics. LED’s are seldom measured in watts due to the light losses as they pass through the optics. Lumen ratings are measured typically at 1m | 3ft and in open air, not water. The 1 metre lumen rating is really only a useful measuring distance for video lighting as most primary lights are required to be used between 5-20m | 16-66ft.
With the LED’s lack of tight beam focus, a 2000 lumen LED may only be a few hundred lumens when measured at 10m | 33ft due to the spread of the beam focus and we find that a 1450 lumen HID actually appears brighter at this same distance.
Here is where it gets interesting and allows you to compare HID and LED. Based on the same 21-watts, you can see that the tighter the beam angle, the further the light will travel. Typically:
8 degrees = an HID canister torch.
12 degrees = an LED canister torch.
70 degrees or more is what is used in video lighting systems, either LED or HID.
*Indicative picture only
Wattage / Voltage = Current used per hour.
Battery capacity divided by current used per hour = expected burn time.
21-watts / 12-volts = 1.75 Amps per hour battery use.
9 Amp battery pack / 1.75 Amps per hour = 5.14 hours use.
This last equation is not linear however. As a battery pack voltage drops, the current used per hour will increase, so the above figure of 5.14 hours may end up being closer to 4 hours.
It is best to allow for 100% more burn time than what you will actually use as battery packs degrade over time. If you will use 2 hours a day, plan for 4 hours burn time when selecting a dive light.
So what does all this mean and what is the best light to choose? It is recommended to buy the best light you can afford for the type of diving you are doing. You will never regret buying a better light.
Recreational divers – canister light LED or HID? If you can’t afford these, you should buy a backup light that takes AA batteries and use rechargeable batteries while you are using the light regularly. As your diving matures, you can replace it with a primary light and move it to the secondary position fitted with non-rechargeable batteries for longevity while you do not expect to use it except in an emergency.
Technical or cave divers – HID canister lights are still the number one choice for primary lights due to tight beams, high colour temperature, and good penetration through silt and water particulate. Tight beams are absolutely essential for clear signalling on a technical dive or in a cave. Rechargeable packs are the best battery configuration for a primary light which should be recharged after every dive, and you will also need good backup lights fitted with reliable non-rechargeable batteries.