Hack a $4 LED Flashlight Into a Scuba Diving Light With a Laxative!




About: I have had a few careers so far, soldier, school teacher, arborist, millwright. I love change and I love learning.

I honestly thought that this would not work because it is way too simple and easy for me to be the first person to think of it. (or at least the first person to publish)  A normal scuba light will run you about $100-$150, renting one usually goes for between $9-$15.

I made a video podcast for the project below.
Please check out my other instructables as well.

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Step 1: Materials

All you need for this project is:

LED Flashlight (I got 3 for $9 from Home Depot and made 2 dive lights)  The lights should also have a push-button switch with a rubber seal and rubber seals at the threaded joints.
A drill with a small bit (I used a 3/64")
A small tupperware container
A small bottle of mineral oil (its a laxative so get it at a pharmacy for a few $)

Step 2: Theory

My idea was triggered by two things...

The first was the movie the Abyss.  Remember when they were breathing an oxygenated liquid?  This allowed them to go to incredible depths because liquids are not compressible like gasses are (see my video for a slightly more detailed explanation)

The second idea was from looking at pictures of people overclocking their computers.  Basically they make their computers run faster than they are supposed to but this causes them to heat up and even melt.  One way they combat the heat is to put the computer into an aquarium and fill it with mineral oil.  The mineral oil does not conduct electricity or corrode components and just happens to be clear.

So if we can fill a flashlight or other device with oil, we can take the pressure off of the seals, the most work they will do is keeping the oil inside on the surface.

Step 3: Filling

The hardest part was getting access to the area between the LED's and the lens.  I was starting to damage the aluminum trying to open it up so I just decided to drill through the back instead.  I used a 3/64" bit and drilled two holes through the circuit board that holds the LED's.  Be careful not to damage the copper traces or the LED's on the other side.

Now as I learned, mineral oil does not want to flow through a 3/64" hole.  I came up with the idea of sticking the drill bit back in one of the holes and running it in reverse so it works like a pump.  You will see air bubbles coming out of the other hole, when they stop coming out, there is no more air inside (provided you are holding it straight)

I put everything in the tupperware and poured the oil in.  Make sure there are no trapped air bubbles as you start to re-assemble the light.  When you are screwing the last part on; push and hold the button in to turn on the light.  Otherwise, when you turn the last few turns on the threads, the rubber will start to push out like a balloon.

Once everything is together, wipe it off, rinse it off and put the remaining oil back into its container.  (I spilled a bunch accidentally and still only used about 1/5th of the container.)

Now due to temperature changes the aluminum and oil will expand and contract very slightly which may cause some seepage. There also might be a bit of oil trapped in the grooves, threads and knurling.  I didn't have a problem with the lights sitting for 2 weeks but I stuck them inside a ziplock during transportation to be safe.

Step 4: The Money Shot!

I was actually down below 95ft, but this is the deepest footage I took at about 88ft

The second light I made was mounted to my camera.

Thanks for reading!

If you have Ideas for other things you could take underwater like this, let me know in the comments, I'd like to try it! Next time I'm going to do a larger flashlight.

Before anyone says it!  I don't think cameras will work well for a few reasons,
1) they are not sealed at all to begin with and would be hard to do so.
2) the index of refraction through the oil would be different than air which would screw up the way the lenses work.
3) the lenses have lots of little gaps inside that would be hard to purge of air.
4) waterproof housings are not that expensive considering what they protect.

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    34 Discussions


    9 years ago on Introduction

    This is great, but I think the greatest part of it is figuring out you could use a drill bit as a pump! Genius, even. Thanks.


    3 years ago

    Thanks for sharing.

    Recently I bought this Powerful Mini Flashlight, looks great and can also adjust the focus range for different usage, Strobe light option for flashing Emergency Signal. http://patriotdeals.com/coupon Use this code "PD10"and save 10%.


    3 years ago

    Great idea, Recently I bought this Powerful Mini Flashlight, looks great and can also adjust the focus range for different usage. http://patriotdeals.com/coupon Use this code "PD10"and save 10%.


    4 years ago on Step 4

    easiest way to get the mineral oil in is to take the air out with a vacuum.

    Great idea! Thanks for taking time to publish this



    4 years ago on Introduction

    it works, but your average 4 dollar led flash light isn't that bright to being. maybe if the local supermarket has 10 of them on sale and you make a chair of them or something


    5 years ago on Introduction

    I've spent a ton of money on flashlights and they all fail due to corrosion and water intrusion. I'm going to give this a try because it makes a lot of sense.


    5 years ago on Introduction

    Well, cool idea, but kind of a pain to change/recharge the battery every time.


    6 years ago on Step 4

    A very simple but very good idea!!!

    I should definitelly try...


    7 years ago on Introduction

    This is genious!! I love ME SOME SCUBA diving!!! And what a cool way to save money!! Thank you for publishing!

    I,m making a super-bright scuba light rated at 1200 Luments, like the $1,000 ones but at a cost of about $300. It includes the batteries ad has a 20 watt LED as the light source.

    9 replies

    1200 lumens WOW. Thats amazing, only 300 dollars too, thats so cheap.

    In case you couldn't tell I'm being sarcastic. Very sarcastic.

    I have a light which caused $50 to build, and is 2200 lumens.

    Another light which was about $70 dollars and is roughly 5000 lumens.

    The lower lumen one is a sst 90 and throws better

    The other one is 5 cree xm l leds and has some throw but mostly flood.
    Both are waterproof.


    Reply 7 years ago on Introduction

    Scuba light need not only to be waterproof as you claim but to withstand at least three times the atmospheric pressure. Yes, may be there are cheaper light out there but yo will not be able to say you did it yourself, would you?


    Reply 7 years ago on Introduction

    i machined my light out of aluminum. its not meant to be a dive light but I think it could take the pressure. I would have to swap out the switch for a piezo. It has a 66mm aspheric lens and an sst90 at 9 amps, powered from 2 lifepo4 26650 batteries. aspheric lenses have problems under water so it has a removable 1/4" piece of plexiglass in front of the lens, but recessed behind a bezel. i don't have a lux meter or a sphere to measure lumens but i'm guessing around 1500-1700 otf and around 2500 emitter lumens based on the binning.

    dave spencerTazo

    Reply 7 years ago on Introduction

    Why would it need to withstand 3 x AP? The concept is like having a water bottle filled 100% with water dyed red. You can take it down to infinite pressures but the red water will never leak out into the surrounding water as long as the lid is on tight. The video in the instructable explains it well.

    UPDATE: my new version is actually going to be 2,174 luments, have a smaller, lighter, li-ion battery and me more energy efficient, AND it's going to be cheaper!

    what type of led? It sounds like your taking the specs off a sst 90. is that otf lumens or rated for the led? What size battery? multiple 18650 batteries? or a d sized lithium? or a square pack? c sized? Copper or aluminum for the body? Modified maglite or custom? Specs?

    it is a luxeon star 7 LED array, it consumes 1 amp and gives out 2174 Luments, the battery is a 13x6x5 cm (approx) Li-Ion Block. it is rated for 18 Amp/hour at 12 VDC


    7 years ago on Introduction

    Nice! Get yourself a bike inner tube and make yourself a sleeve to go over the cylinder, one more layer of waterproofing and it will hold your oil in.