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Eternal Flame Indestructible LED Lantern

Build simple, rugged, floating LED lanterns that glow for days.

Eternal Flame Indestructible LED Lantern

If you’re like me, you’re the bane of hardware store employees. I wander through the whole place picking up everything, looking at possibilities more than parts. Can they help me find anything? “No thanks,” I answer. What am I working on? “I don’t know yet,” I say. They move on, keeping a suspicious eye on me.

Some things just seem useful, even if I can’t think of how at the moment. One time I found matched pairs of PVC caps and plugs that fit together into little airtight pods of various sizes. For what, I didn’t know until I wanted a way to float lit LEDs down a stream.

The result: simple, rugged, floating LED lanterns that glow for days. They’ve survived being submerged for a week, frozen, and laundered in the washing machine. I even hit one with the lawn mower, and it still works. When they get dirty, just hose them off.


Step #1: Drill the hole for the LED.

Eternal Flame Indestructible LED LanternEternal Flame Indestructible LED LanternEternal Flame Indestructible LED LanternEternal Flame Indestructible LED Lantern
  • Drill a hole in the top center of the cap using a 3/8" bit; it’s just under 10mm and will make a watertight fit for the LED.
  • Use a drill vise to prevent kickback. To protect the cap from scratches, you can line the vise jaws with tape or cut a V in 2 pieces of scrap wood.
  • In the original article, author Steve Hoefer was pictured wearing gloves while using a drill press, which is a safety hazard. “Gloves are a no-no around rotating tools,” Steve admits. Thanks to reader Tim Kemp for pointing out the error.

Step #2: Prepare the LED.

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  • Cut about ½" (13mm) off the end of each LED lead, so they’ll fit easily inside the lantern. Use pliers to bend a small dogleg in the longer, anode (+) pin. This will keep the shorter, cathode (–) pin from accidentally shorting out the side of the battery.
  • Finally, for watertightness, put a single wrap of thread sealing tape around the base of the LED.

Step #3: Insert the LED.

Eternal Flame Indestructible LED Lantern

Place the LED in the pliers so that their blunt nose is flush against the bottom of the LED lens. This will let you push the LED firmly without mangling it. Push the LED through the cap from the inside until it’s flush with the inside of the cap. If the fit is too tight using just your hands, use the open end of the plug as a backstop and gently tap the handle of the pliers with a rubber mallet.

Step #4: Insulate the binder clip.

Eternal Flame Indestructible LED Lantern

The enamel coating on the binder clips can insulate but tends to chip. To avoid shorting out your LED, apply electrical tape inside the clip. The pliers can help hold it open.

Step #5: Power on.

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Slide the coin cell battery between the 2 LED leads, with the smooth (positive) side against the longer lead. The LED should light up. Clip the binder clip over the top to hold the leads securely to the LED.

Step #6: Close it up.

Eternal Flame Indestructible LED Lantern
  • Wrap the top edge of the plug once with a strip of sealing tape to keep any water out. Then squeeze the plug into the cap.
  • If you plan to use the lantern in water, make it easier to retrieve by drilling a small hole in the edge of the plug and tying in some fishing line. The lanterns tend to float upright; but if you want them to sink, add some fishing weights or steel nuts before final assembly.
  • When the battery or LED has reached the end of its useful life, a firm twist will loosen the assembly for replacement.

Step #7: Illuminate.

Eternal Flame Indestructible LED LanternEternal Flame Indestructible LED LanternEternal Flame Indestructible LED LanternEternal Flame Indestructible LED Lantern
  • Use your LED lanterns anywhere you’d like some durable illumination. They’re better in large numbers, and you can get interesting effects by using flickering or color-changing LEDs.
  • I’ve used them to light up a yard party and to mark the trail for night hiking. I’ve floated them downstream, frozen them in ice, even used them as ammo in a pneumatic cannon. What you can use them for is limited only by your imagination.

Steve Hoefer

Steve Hoefer is a creative swashbuckler, freelance writer and inventor. He regularly contributes projects to the pages of MAKE and his inventions have appeared internationally on TV, radio, and print. He lives on his family farm in Iowa.


  1. Steve Hoefer says:

    Thanks for the comment on safety Tim. I’m super aware of lose clothing and hair around power tools, but I had always considered my skin-tight, extra grippy gloves a feature that made working around power tools safer (material and hands less likely to slip, etc.)

    Your comment spurred me to consult with a few machinists and found that ”any” gloves are a no-no around rotating tools. The OSHA guidelines are [|here] (See page 37 for the hand/arm protection.)

    I stand corrected!

  2. Steve Hoefer says:

    No, there is no current regulating resistor in the circuit. Using one would extend the life of the battery, but it’s not necessary and most LEDs will give days, if not weeks of light when attached straight to the battery. For more on why (besides that it would double the complexity of the project) see the excellent Evil Mad Science Labs research on [|LED Throwie-like circuits].

  3. Steve Hoefer says:

    If you’re worried about littering waterways with plastic and batteries, take note of step 6 where I recommend attaching some monofilament line so they can be easily recovered. (All of the lanterns used in the photos were recovered and have been reused multiple times.)

  4. Tim Kemp says:

    Gary, that is a very good point. The reason it doesn’t burn out the LED or start a fire is that lithium coin cells have quite a bit of internal resistance. I searched on-line and found [|this explanation].

  5. Steve Hoefer says:

    I added a few fishing weights to the lantern before I closed it up so that it would sink, then dropped it into a plastic container full of water and froze over night.

    If you want the water to be more clear try using distilled (not filtered) water and boil it 3 times to remove some of the disolved gases that cloud it up.

  6. Goli Mohammadi says:

    That sounds gorgeous, Tracie! We’d love to see pics of that.

  7. Goli Mohammadi says:

    What a great idea, Peter! We’d love to see pics of that in action!

  8. Peter Natale says:

    Well, I’m trying my best, but I just can’t seem to get the battery to stay put. I tried a binder clip, but it’s not working. Any other thoughts?

  9. Peter Natale says:

    So, here I am, a week later. I have ten color changing lanterns that sink to the bottom of my pool and are waterproof. I upgraded from teflon tape around the plug to an o-ring because the tape kept ripping off. The only problem I’m having is getting the battery to stay. Binder clips won’t work for me because it gets pushed by the hot glue and BBs I used to weigh them down. So far, I’ve been using cellophane tape to hold the batteries in, but it’s a pain and not exactly reliable. Does anyone have any thoughts?

  10. Tim Kemp says:

    A releasable cable tie with some inner tube rubber under it to keep it from sliding?

  11. Steve Hoefer says:

    The spacing is pretty tight. You can use pliers to remove the handles from the binder clips (just squeeze them together) to give you more space.

  12. Steve Hoefer says:

    Evil Mad Science is the go-to source for these.
    The ones used here are their 10mm diffused warm white
    They won’t be nearly as bright as other LED’s but they produce a very effect.