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Make a DIY underwater canister dive light for scuba diving

Making an L.E.D dive light? New design for LED's in a Mag-Lite and Check out the LED Genie LED Driver

Page 1 Page 2 Page 3
What you need to know before ordering parts and building the light.
How to build the canister dive light with lots of pictures.
Dive Light Genie Electronics Info.

Copyright: All pictures, electronic design and concepts on this site are copy written. Copyright Matthew Skinner 1st May 2005. Please contact me before reproducing any contents from this web site.

Here is my first DIY dive light after its first SCUBA dive. More pictures at each step of the building process are on page two.

DIY homemade dive light.


Design Requirements

After seeing a few HID and MR16 halogen canister underwater dive lights I wanted to build my own. The main reason for looking at DIY dive lights was that commercial lights cost around us$500+ here in Australia for basic models which were far from perfect for my needs. After searching the internet I came across a few different designs and none were foolproof or well thought out in the existing DIY dive-light pages. Either the designs required expensive tools like a lathe, took a long time to custom make parts, or the light was not strong enough to withstand enough water pressure.

I wanted an under-water dive light for scuba diving which was.

  • Brighter than a 10 watt HID canister dive-light.
  • Outputs white, not yellow light with even light coverage for good photography and true colors underwater.
  • Small and streamlined as I hate gear hanging off me underwater.
  • Cost effective.
  • Quick to make with common parts.
  • Reliable to at least 40m / 130ft deep.
  • Flexible to suit all diving conditions.
  • Good burn time, with enough power for 1 to 2 hours of burn time.

I dived with others who owned 35 watt halogen canister dive-lights which used SLA batteries, however they produced less and yellowish light when compared to HID dive lights for numerous reasons which was not the fault of the globe. After multiple dives it was clear that 40 to 50 minutes was all they would run for which was not enough time to walk to the shore, wade out and snorkel to deep water, go for a 1 hour dive and then swim back to shore and find the car. Most shore dives at night that I do regularly needed 1.5 hours of torch life from the moment I leave the car to when I have packed the gear back into the car, so the cheap lights did not fit my needs and the ones that did cover my needs were well over 4-5 times more than what I could build a much better custom underwater canister dive light for.

The quest had begun..

Globe / Lamp / LED

Having a background in professional stage lighting for years I know a lot about lamps, from how to look after them for optimal life, to choosing the right one for the job. For primary diving lights there are three commonly used types, Halogen, HID and now LED. LED technology is now bright enough to easily overpower both a 10 watt HID and 50 watt Halogen. LED has many advantages then the other two mentioned, so I have now added instructions on how to install LEDs into this maglite build if you do not wish to use Halogen which is a cheaper solution. Halogen when over driven (more on this below) is an excellent choice when you need to use a light for both narrow beams on one dive, and then a wide flood as a video light on another. Being able to change is probably Halogens only advantage over LED.

LED Globes

I get a lot of people emailing me asking what the LED globes that are sold in stores are like, the answer is not very good. LED's need to be kept cool otherwise they will overheat and stop working. The globes sold in stores are designed to replace halogen globes around your house using air cooling in places with very little air movement. Because they are designed to work in fittings which were designed for hot halogens, they need to limit the performance of the LED's to prevent them from over heating and failing to work. This means the globes are producing less light so the globe does not overheat and then stop working after a few minutes of use. Luckily for divers we have water all around us to keep the LED's cool, and this allows us to make an LED which far out performs anything you can buy ready made in a shop. Getting rid of the heat does require a special heatsink, and I am now producing and selling these so you can make a high performance LED dive light with no special tools.

Disadvantages of HID when compared to LED

I'll speak very generally about the most commonly used lamp and ballasts in HID dive lights at the moment, advances are being made as HID are used in car headlights which is forcing them to be improved and developed. LED's are being improved at a much faster rate.

  • HID's start 1000 times best case, so you can not turn the light on and off a lot of times before the globes life is over, regardless of the hours the globe has done. The ignition of the HID globe is very harsh and the life of a HID is a combination of running hours, the number of starts as well as a lot of other factors. LED can be started and stopped as many times as you like without damaging the LED or reducing their 50,000+ hours of life.
  • To get close to the 1000 starts, the HID ballast needs to take around a minute to turn the globe fully on, up to correct color and to stop flickering. If the ballast does it faster then the start-up ignition of the globe is more damaging and you'll find your globe blows after less starts then 1000. This means you can't get lots of light quickly. LED's can start instantly with no flickering and without reducing their life.
  • When you turn a HID globe on you should not turn it off again for at least 2 minutes to look after the expensive globe. So for looking in ledges during the daytime where the light is turned on and off for a quick look the HID globe will blow very quickly. LED's can be turned on and off as much as you like without a reduction in life span.
  • The globe will not re-strike when hot. This means if you turn the HID off you can't turn it back on until the lamp cools, which can take a few minutes if the ballast looks after the globe correctly. Most ballasts will allow a re-strike after 20 seconds or less, once again at the loss of lamp life. Some ballasts also support hot re strike but these are not common and always cost a lot more and once again are at the expense of less life from the expensive globe. LED's can be turned on and off as much as you like without a reduction in life span.
  • When the HID globe exceeds its life span there is a small but very real chance of the globe exploding, which could break a thin lens and flood the light. Video projectors use timers to keep track of how old the globe is to warn owners when to replace the globe to avoid damage to the video projector. I have not seen any dive lights with this feature yet as thick glass solves the problem. LED's do not explode.
  • Very difficult to source spare HID globes when over seas in remote places. LED's with 50,000+ hours are likely to out live you in a diving light.
  • Very costly to replace or keep a spare HID globe. LED's with 50,000+ hours are likely to out live you in a diving light.
  • They run on a few thousand volts making them more dangerous to use around water. LED's run on low voltage, some as low as 3 volts.
  • HID are less reliable and more expensive than halogen. LED's are even more reliable and will also be cheaper when you factor in the life span of the light.

These are the reasons why most manufacturers have stopped producing 10 watt HID dive lights in favour of LED technology. Shortly they will also take over the 18 and 24 watt HID part of the market.


Over Driving a Halogen, lamp life and cost.

As mentioned above a Halogen based light still has a few advantages over LED, by being easy to change the globe between dives. When on a budget the ability to change from a normal dive light to a video light can save you a lot of money and the need to have two different lights. Halogen based lights are also easier and cheaper to build then LED, although this is quickly out weighed by the extra burntime a LED will give from the same sized battery pack. Halogen can be made to create white and lots of light that will over power a 10 watt HID, you can do this at the cost of reduced life of the $2 halogen globes by over driving them. This can be done without reducing reliability by using a Dive Light Genie.

A HID will last <1000 hours in ideal conditions when creating white light, and a halogen will last around 200 hours (depending on how high a voltage you use) when creating the same white light under ideal conditions. HID lamps cost us$100 and up, compared to us$2 for a cheap halogen lamp. It makes halogen lamps overdriven very good value for money, especially when you consider how many hours you are likely to go diving with a torch in a year. Another good reason is if the light head is flooded which may happen, a cheap mr16 is not a big deal to replace and all stores keep them in stock even in remote places. ie on a diving holiday. All globes including HID will produce nice light when new, and as they get older will dullen and change color, an old HID lamp will no longer be as bright and white as it once was when new, the same is true of halogen. The cost of putting in a new globe makes halogen very attractive.

Beam angles is another consideration I took into account when choosing the lamp to base my DIY dive light on as a narrow beam (spot) looks/is brighter and penetrates dirty water without backscatter much better than a Flood (wide angled globe). This is the reason why commercial HID lights look to be so much brighter than halogen lights as the HID globes normally have a much narrower and tighter beam of light. People rarely compare apples with apples and think HID is the best you can get which is not really the case depending on what your needs are. As some dives I would want a flood 38 degree to light up a huge area evenly, and other dives I would want a spot 10 degree light to reach further, I found cheap halogens allowed me to change the light to suit the dive and conditions. A 10 degree spot in dirty water not only allows you to see further it also makes signaling to a buddy much easier. Try doing an OK signal with an underwater flood dive light, it just does not work and you end up blinding your dive buddy with your underwater torch. Sorry to anyone who dives with me when I take the light and camera :)

To give you an idea of the life of a halogen globe at different voltages.

10 cells = 12.0 v = 6,000 hours
12 cells = 14.4 v =1,500 hours
14 cells = 16.8 v = 350 hours
17 cells = 20.4 v = 120 hours
18 cells = 21.6 v = 50 hours

The same is true of dimming the globe below the rated voltage.

Lamp Life
2 x
4 x
20 x
> 20 x

This table shows the amount dimmed does not translate into a linear energy saving, this is why the overdriving works so well at the expense of lamp life. The current stays roughly the same as you increase the voltage, so the burn time is not reduced and extra light at a whiter color is created. It will turn a 50 watt halogen globe into a 70+ watt globe due to the extra voltage.

Torch head

Choosing the underwater dive torch head was an easy task, I wanted a very bright canister dive light and this meant HEAT and lots of it, so an aluminum light head and glass would be needed to conduct the heat away from the globe. To deal with the heat a modified aluminum Maglite torch was the best solution to making the torch fast and cheaply. The picture below shows the C sized Maglite (any C or D sized Maglite will work) end with a MR16 halogen globe inside. Below are diagrams for two different ways to seal the light, the first being easier to source the parts (1 piece of glass and 2 orings) and build with the second method being stronger. I personally went with the second method which requires two pieces of glass to be glued together as I felt this would withstand more water pressure and be more reliable due to only 1 oring. Getting some glass that's the right size can be difficult for the smaller diameter to form the step, but if your keen and ring around some places have some scrap that they allow you to have.

Good news is that no mods are needed to change from one design to the other, so you could always build the easy mod first and upgrade to the second way in the future. The standard zbattery lens by itself should be fine to < 30m depth but please do your own testing and let me know how you go.

To protect the globe and lens from heat when its used out of water, I used the Dive Light Genie which will allow you to dim the light to create less heat when above water or else you burn yourself on the Maglite after a few minutes of use at full power. The larger top piece of glass can be purchased from www.zbattery.com or anywhere that sells police or army supplies. The smaller lens for the second design is custom made by a local glazier for not much money as I ground it smooth on the edges myself. The advantage of this stepped lens design is that the water pressure sucks the lens onto the Maglite the deeper you dive and improves the seal. The same design is used to seal the otter box and just about every dive light on the market, its a very proven design. The glass is also suspended by orings and not hard against metal which is yet another reason to go with the stepped lens.

This picture shows the EZ Maglite mod drawn by "fhman" which is easier and cheaper to build however I feel it's not as good as the harder to build stepped lens which is shown below and also shown in more detail on page 2.

ez maglite mod for an easier water tight seal.

How to fit a halogen mr16 into a maglite for a dive torch..

Here's the stepped lens design which does not show the original o-ring above the glass to fully shock mount and isolate the glass from metal to glass contact if its dropped or the metal is not perfectly flat. See page 2 for more pictures on this design.

maglite with mr16 globe modified for a scuba dive umbilical torch.




(Schurter Part # 1241.2411.7 )

To my knowledge I was the first person to use a piezo switch in a dive light and had to do a lot of emails with the engineers at Schurter before purchasing one for my light. They are great as they are designed to be used in vending machines where vandals are going to try and break the machine. Very robust, machined from a solid piece of metal and have no moving parts or air spaces. They may cost the most, however they have no maintaince and installation is as easy as drilling a hole and using JB weld to glue the switch in place and create a water tight seal with the glue.
Reed These are cheap however they are harder to install and get working as there are a lot of variables to think about. I spent a long time fine tuning the premade light heads that I sell to give a good tactile and reliable action. Huge advantage is the switch does not require a hole or any weak point that can leak. Using a magnet that's too strong will interfer with your compass, not strong enough and the switch won't work and that's only 1 of many considerations with a reed.
Toggle I dislike toggles as you rely on a thin rubber boot to keep your light water proof and you can't really mount these on the light head. The rubber perishes and needs to be inspected and replaced every few years, also one little cut from a metal wreck and the light leaks. They are easy to install and also cheap to purchase however for a zero maintaince light I prefer the above two types of switches.




Choosing the battery.

Since I am aiming at a 50 watt globe this means for a 1 hour dive, a 4.5ah battery pack will be needed roughly as a bare minimum as batteries don't give you the full ratting over 1 hour, but over a 10 hour drain. The faster you drain a battery the less efficient it is at giving you back all of the stored charge. To work out the ah rating for a 1 hour burn time you use the formula, Watts / Voltage = Amps. When overdriving you don't use much more current so base all your calculations as if you are using 12 volts to make things simple. The globe is designed to be 50 watts at 12 volts so we use these for any calculations. For an example, 50 watts divided by 12 volts is 4.2 amps. If you were to use a 4.5 ah pack without my dive light genie electronics you would find you would only get around 46 minutes of burn time this is due to the efficiency mentioned above, however due to the voltage regulation and other unique features the DLG, my electronics gave me back the time I needed for a 1 hour dive without needing to use a smaller globe or larger battery and hence canister. I find the battery lasts >30% longer just by having a Dive Light Genie installed. This is explained on page 3 of this guide as to why this happens.

As Ni-Mh and Ni-Cad have very flat discharge curves, they are difficult to measure how much charge is left in them, they also very quickly drop to 0v not giving a warning that they are almost discharged. This makes it difficult to ensure the battery is not over drained which will damage a battery, and that you have enough time to finish your dive before the light goes out. I designed the dive light genie to overcome this, to give some warning and to protect the battery.

So a good choice for an underwater dive light battery pack is either SLA because they are so cheap and are already available in 12 volt packs, Ni-Mh for their small size and weight and greater life, and also LiFePO4 batteries. The more advanced a battery is, the more care they need to have a long life and hence why I designed the electronics to take care of these considerations for the scuba diver.

In the end I wanted a small dive light canister to keep me streamlined underwater, so NIMH was chosen over SLA due to their size and weight. I didn't consider Li-ion, LiPo and LiFePO4 packs because of the complications a charger for these cells present which can be overcome with PCB's inside the battery pack. If you do not have a PCB inside a lithium pack then you really need a charger to charge each cell by itself so that each cell will be discharged at the same time in the pack. What can happen is that one cell becomes empty, but the combined voltage of the other cells is still above the voltage of an empty pack. With Ni-Mh this happens but is solved by slow charging or a fast charger like my design which will fast charge and then use a slow charge at the end to balance the pack. This is why slow chargers for nimh are so popular as they eliminate the pack from going out of balance and this is why I think NiMh is still better suited for most people doing DIY.

With LiFePO4 cells having the advantages of Lion/lipo without the disadvantages, they are promising and worth considering as some cells allow you to screw them together with no soldering making them great for DIY. If your interested then have a look at these cells LiFePO4 with M6 screw thread. Two of those cells would work really well with some LEDs and would make for a very small light.


Ni-Cad Lion and LiPo LiFePO4
Cost, weight and overall size of pack.
Very cheap to buy, but very large and heavy.
Good balance of size, weight and cost. A big jump in price when compared to SLA.
Cost half the price of Ni-Mh but the size will be around twice the size of Ni-Mh to get the same output. Size and cost would both be somewhere between the SLA and NIMH. Cost around twice the price of NiMh, but these are light weight and also very small for large Ah packs. Around half the size of a Ni-Mh pack. If the light gets flooded its a lot of money to loose. Cost around the same as Ni-Mh when comparing the same Ah size. The packs will be only slightly smaller and 30% lighter so these are a good choice for divelights.
Storage and Usage considerations
Don't like to be stored fully discharged as this can damage them. Keep them 70% or more charged when stored. Don't like to be deep cycled, ie fully drained and charged which is what happens in a dive light.
Prefer to be used often which gives them a larger capacity or left empty which reduces their capacity until deep cycled a few times. Very Sensitive to being fully discharged and also overcharged.
They are way more robust and wont be damaged as much as Ni-Mh will be by 100% discharge or overcharging. Don't like to be stored at full charge and like to be deep cycled. Need to be stored charged or else the protection circuit can prevent the pack from being re charged. These are much safer then Lion as these are said to not explode if abused like Lion packs can. Can be made up with no protection PCB if a Dive Light Genie (or LED Genie) is used to prevent over discharge.
Storage Continued.
they lose 5% of their charge per MONTH. read above as you need to top them up every few months in storage.
They lose about 10% of their charge in the first 24 hours, then about 10% per MONTH after that. In warmer weather the faster they discharge.
About the same self discharge as Ni-Mh Slow self discharge rate. Slow self discharge rate.
Voltage drop over the use on a dive.
The voltage drop is very linear to the % of charge left, easy to work out how much charge is in a SLA. A 12 volt SLA will be at 12 volts when its 20% full.
The voltage is very constant over the discharge curve. Ie around 1.2 volts for 80% of the discharge. Almost no warning light will fail.
About the same self discharge as Ni-Mh Almost no warning light will fail. Even more constant a voltage when discharged at 3.6v per cell, almost no warning. Even more constant a voltage when discharged at 3.3v per cell, the least amount of warning.
Life cycle
300 - 500 charges in a lifetime
1000+ charges in a lifetime although the requirements for a light means they will be easily damaged if totally discharged or overcharged.
About twice the life of Ni-Mh, although they don't get damaged as easily so most likely they will last even longer. The technology is very new and every few months the chemistry is changed and improved. I don't think these will last anywhere near what the spec sheets claim. Mobile phone LION batteries only ever come with a 6 month warranty for a reason. >2000 cycles and the pack will still be 80% of it's Ah rating. Better cycle life than nimh making them better value. Still too new, nimh is very mature technology and proven over time.
Charging and Discharge Considerations.
Easy to charge, every car has a charger built in. Simply plug the SLA into the cigarette lighter to get a top up on the way to the dive site. They don't like to be heavily drained too many times.ie a 5ah pack should not be drained faster than 2.7amps over an hour. But they don't mind being drained at 40 amps ! for up to 5 seconds at a time. The light will give a good warning that the batteries are low and about to die, Ni-Mh and Ni-Cad give almost no warning.
Very very sensitive to overcharging and also over draining the cells. Must stay above 1 volt per cell or they get damaged. This means the instant the light begins to weaken the light should be turned off, you don't notice its getting low until its too late most of the time. Also difficult to charge if in a made up pack of lots of cells paralleled together. High risk of being damaged in a torch application.
Can be damaged by overcharging or over discharge but are robust enough to take the demands of a torch without any special electronics. You could use the light until it no longer has enough power to make the filament glow and still not do serious damage to the batteries. Charging and discharging is very critical for lion, so much so they normally come with protection circuits fitted as the packs can explode or create fires if used wrongly. I won't go into LION in depth here as there is simply too much to list and the info is changing all the time as the lion chemistry is being improved. Very sensitive to both over charging and discharging, but will not explode like Lion. Can be made up with no protection PCB if a Dive Light Genie (or LED Genie) is used to prevent over discharge and the correct charger is used that will balance the cells when charging. Some PCB's that you add to the battery pack will balance the cells and prevent the pack from being used for 30minutes after a charge. Ni-Mh is a lot simplier to use.


A huge saving can be made if the larger SLA type batteries are used so if cost is important read the section of battery types above and make a choice on what you find more important. Here's a picture of a cheaper SLA dive light using the otter box 3500 as a canister to hold a SLA. The switch is a magnet which moves over a reed switch inside the Maglite, this means no holes are made for a switch. SLA are much larger and are only 12 volts so the light is not as white, only two of the reasons I spent the extra to make a Ni-Mh version.

Here's a light built by Claustrox using the otterbox 3500 and a SLA. After a few months of diving he made a Ni-Mh version as its worth paying to get smaller and lighter NIMH cells.

Cheap SLA dive light using a otterbox for a canister.


This picture shows how my dive light fits 14 C sized batteries inside my canister before the umbilical lead is fitted for the torch head. The cd is showing the size of the largest side of the dive light canister as this is very small and the whole canister fits inside my bcd pocket ! Please be aware that it does not show the way my pack is wired. After building my own and a lot of people emailing and asking for this pack to be pre made, batteryspace have now started to offer this pack pre made. Click here for details.

nimh battery layout for diy homemade scuba dive light.


Dive Light Canister Choice

For the canister I considered making my own out of PVC pipe, however the time spent building and sourcing the pipe with a thick enough wall was difficult in Australia at local hardware stores. Sewerage pipe was a good candidate, however I really wanted a clear canister for the backup LED lighting in the canister that I had in mind with the electronics. After a lot of searching I came across the www.otterbox.com range of pre made water proof cases. They are rated at 30 meters or 100 feet and could easily be pushed much further as plenty of people including myself have already done many times to 50m. Advantages of the otter box range is they come in clear or colors, were ready made, pressure tested, had a belt clip and lanyard pre installed, and not to mention the latches for holding the lid down was already supplied and fitted. The price of stainless clips and the cost of glue and plastic would probably end up more and I would have to do a lot of extra work, possibly needing a lathe which I don't have access to. For the asking price of these I couldn't justify wasting time making my own. I worked out the otter box 8000 could be used for a 12 volt battery pack, or if I wanted to overdrive the globes, more room would be needed and the 9000 model was then the perfect size. The result was a cost effective ready made canister that didn't lower the quality of the home-made dive light. As I wanted a high performance and very bright light, the dive light canister needed to hold 14 C sized batteries to over drive the globe.

At first I was worried about a plastic canister however on one of the first dives I dropped the canister with battery inside 4 feet onto a large rock. I was worried about cracks as it was a nasty fall onto a sharp rock, however on inspection the plastic was not even marked. I am surprised just how tough the plastic is which I think it is made from poly carbonate which is a strong material.

Dive light parts and sources



JB Weld Kmart stores across Australia, Wal-Mart in the USA.

www.otterbox.com you can find cheaper online stores if you look but being from Australia it's hard to find a store willing to send OS.

9000 model otter box for Ni-Mh C cells, or the otter box 3500 fits a 7ah SLA very nicely.

Selley's Araldite Ultra Clear glue for glass lens. Hardware store.
52mm Maglite Lens www.zbattery.com
49mm inner lens local glazier, custom ground.
sand paper, wet and dry Hardware store.
Batteries, shrink wrap and terminals etc. BatterySpace Pre made pack
Cable Glands IP68 I now stock better glands than the ones used in this guide, see below for a picture and pricing.
Phillips MR16 lamp Hardware or lighting store.
Mag-Lite ebay for a second hand one since it was going to get cut into pieces.
Piezo Switch RS Componets Use the site search to look for "1241.2411.7" which is the Schurter part number or the RS Part number "456-1852". They have 4 colors to choose from. Stay away from any model with a LED ring of light or a tactile feel as they are not machined from a solid piece of metal without any seals that can fail.
Charger I used a DIY NIMH Smart Travel Charger Kit to build my own.
Cable, submersible grade. I have this in stock and can send it to anyone who orders another product from me. Electrician suppliers carry mains cable, just choose a cable rated to go under water.


A pair (two) of cable glands with strain relief to suit cable between 6.5mm to 8.8mm. Thread is M16x1.5 and is 6mm long.




Tools Needed

  • Drill Press.
  • Clamp or vice for drill press.
  • Metal hand file or angle grinder which is faster.
  • Drills.
  • Hole Saw with sprung teeth in multiple sizes.
  • Hacksaw
  • Soldering Iron or you could use crimp or screw terminal blocks to join wire.


Custom Electronics

Please note all information on the dive light genie HALOGEN electronics can be found here. The LED Genie is a driver for LED's with some unique and handy features.

I've now uploaded a video demo of my electronics in operation, to keep it a small download I didn't show off all the features only how simple it is to change the level of light. Download or watch underwater canister dive light demo video.

The electronics I designed for my light are useful in any light, even if the light is running at 12 volts and is not being over driven with a higher voltage. All of the features will benefit any dive light and can be retro fitted to any DIY dive light or commercial dive torch which has been store bought. The electronics are now available in kit form and pre-made. The design is copy written and patent's are applied for.