Waterproofing a zoomie

The topic shows up from time to time….
Most zoomies are not waterproof. The reason is that while zooming, they need to move air in and out of the body which doesn’t allow them to be fully sealed.
I wanted to compile a number of ways to let the air in and out while not letting water in. Or to otherwise make the light give at least very basic waterproofing guaranties.

1. Tight o-rings.
With this method zoomie is sealed while the bezel doesn’t move but breaks the seal while zooming


  • cheap
  • simple
  • tried and tested


  • very stiff zoom travel
  • not fully waterproof while zooming

2. Internal zoom, camera-lens style
With camera lenses there is no air movement in and out, so the body can be fully sealed


  • tried and tested (in cameras)


  • expensive
  • bulky

3. Internal zoom, enclosed lens
One can build a regular zoomie but enclose the entire bezel in another box. That other box can be waterproof because again any zoom travel doesn’t change volume of the light


  • works well under water


  • bulky
  • somewhat less throw due to smaller lens

4. Secondary internal lens
Don’t try to waterproof the entire interior but only the electronics. Put a flat waterproofing-lens below the main one, fixed to the main body. The light is much like a mule with a moving aspheric put in front of it. Note: you can use a pre-collimator lens instead of a flat one. Either TIR or spherical.


  • quite simple
  • reasonably compact


  • applicable only to aspheric zoomies, not TIR ones
  • water ingress below the lens may force interior cleanup

5. Fixed lens, moving pill
Volume doesn’t change, so no problems with waterproofing the lens.


  • I fail to find any


  • the light is always in the largest position which adds bulk
  • moving the pill is complex, especially if it’s done in a waterproof way
  • poor thermal path from pill to body

6. Lock-seal
Seal that engages only when the bezel if fully retracted. The light is waterproof in flood mode, but not in throw or intermediate. You probably want to store the light retracted anyway, so it’s waterproof then.


  • quite simple
  • compact
  • cheap


  • not waterproof while zooming

7. Membrane
Gore-tex style membrane allows air to move in and out but keeps water out


  • compact


  • untested, novel, may or may not work well

8. Conformal coating
Let the water in but protect the electronics by:

  • coating the LED and wires with something waterproof (except for LED lens obviously)
  • sealing wire holes and pill (if there’s one) so water can’t enter driver / battery compartment


  • compact
  • lightweight
  • inexpensive
  • does not have to be designed into the light - can be applied by modders


  • any water ingress may leave residue on LED dome so you’d better clean it up with IPA after such event
  • makes LED swaps more effortful

9. Driver seal
Like above but don’t apply conformal coating. Be sure to use a driver with LVP and thermal protection.


  • simple
  • compact
  • lightweight
  • inexpensive
  • does not have to be designed into the light - can be applied by modders


  • any water ingress may leave residue on LED dome so you’d better clean it up with IPA after such event
  • water can cause a short. The light will stop working then and battery may discharge. But current is still regulated by the driver and can be reduced when the light overheats. This should be enough to prevent damage.

10. Variable-shape lenses
A lens that changes shape to provide zoom


  • cool


  • expensive
  • low performance (the working area of the lens is very small)
  • untested

The best zoom would be completely electronic, using no mechanics. An integrated led matrix on MCPCB, and a driver, which can handle it well.
I don’t know if any led producer made this kind of emitter so far, probably would be pretty expensive. This way the emitter surface could be changed between huge limits. 7x7 matrix would be enough for all needs. 3 lm/cd to 147 lm/cd. That would be my dreamflashlight in a simple angle lamp host.

The concept of LED array in a zoomie has seen some discussion already:

Thanks for this thread Agro!

I have some Lidl zoomies to mod and these indications gave me some ideas.

Those are 2xAA that will become/take 2x14500 with XHP50.2 leds, and custom copper heatsink by kiriba-ru. So, it will become an expensive light to damage…

My idea, seeing what you posted above, is to applicate some non-conductive silicone on the top (covering the wires to the MCPCB and other possible water entries aroun the led/board) and on the driver (just leaving the spring “clear”) to avoid any circuit/component to get wet.

I tried the tight o-rings but it makes zooming less effective and stiff.

The other rings, I’ll just lub them.
Thanks for your work!

Ziplock bag.

Just say no to Zumiez. Huh. It looks like Google voice keyboard doesn’t even recognize them.

Thanks, nice thing to read.
I hope flexible surfaced emitter will be available for us in the forthcoming years, would be glad to see.
Nice ideas and broad spectrum of solutions from you though. Looking forward to see them realized as well!
Good luck!

Please report back when you try this method, I would love to see it. :slight_smile:

Is it really worth the agro-vation to try waterproofing it?

One possibility would be to treat the light as 2 pieces. A mule, plus a lens-holding head. Make the mule as waterproof as need be, even with a clear lens + inset bezel to hold it, with a domeless LED almost pressing against the glass.

Then have a snap-on or screw-on head as a separate piece. Lube any screw-threads very well, and it should keep most water out. Might not be waterproof as to be able to use as a diving-light or anything, but should be enough to keep it dry inside even in heavy rain.

Regarding your mule idea:
The mule portion would have its own lens and be fully waterproof.

The sliding bezel could then be intentionally not waterproof. Perhaps put large openings in the side so water can flow out of it. And/or make it easily removable so the back of the aspheric and top of the mule lens can be easily cleaned.

Regarding some of Agro’s ideas to have internal moving lenses:
Having the sliding lens completely internal solves one problem… the light no longer changes volume so air pressure attempting to equalize wont’ cause the bezel to change positions.

But it creates another: If the light is completely sealed and does not change size, mechanically how do you cycle the zoom mechanism?

  • Do you install a motor? … that’s heavy and bulky
  • Maybe use magnets to move the lens? … but that means the light isn’t suitable for EDC in your pocket next to your wallet.

I have a budget zoomie that does not change shape when the zoom is cycled. It has a fixed lens and uses a rotary dial on the outside of the light to move a pill containing the LED back and forth. This is an inferior solution:

  • The entire light is quite bulky since there is a lot of empty space inside the light at all times.
  • It is not waterproof because the dial is connected to a gear mechanism that moves the pill back and forth.
  • This setup has just about the world’s worst heat management for the LED since the LED is on a tiny alumimum pill that is not tightly fitted to the body.

Some of these problems are solvable… add o-rings around the rotary control for waterproof. Have the gear mechanism move the aspheric lens instead of the pill. Place a flat lens ahead of the aspheric lens so internal volume does not change.

But this still wouldn’t fix the problem of the light being very big and bulky due to all the extra empty space inside the light needed for the lens to slide back and forth. In an EDC zoomie is it really worth adding an extra inch of length to the light just to try to make it waterproof? …. it would be much cheaper and easier to make a waterproof zoomie simply by adding screw threads to the bezel and adding o-rings to make the zoom cycling extra-stiff. That solution is already used by many lights and is much more compact.

I believe it’s #4 on the list…or maybe I don’t understand it?
It’s among my favorites as well. :slight_smile:

Please note that that size-pessimization variants (moving pill, flat glass in front of the main lens) are not that much larger when the lens has a very short focal length, f.e. when using a TIR. But then - I don’t really like anyway as they are quite complex and don’t seem strongly advantageous over internal flat glass.
Nevertheless I added the moving pill to the list - it was new to me. :slight_smile:
Out of curiosity, how many zoomies do you have?

BTW I find your idea of having large openings curious. They would add extra surfaces that need frequent cleaning but then it would make cleaning them easy. Maybe this would enable some different assembly techniques…need to think about it some more. :slight_smile:

“Secondary internal lens”? Huh?

No, I mean take a regular SK98 or so. Pop off the head entirely, so that just the tube assembly is left. Make that absolutely waterproof as if it’s a regular tubelight like an S2+. Pot the internals, double the O-rings, do whatever it takes. But instead of having the exposed LED in front, put a plain piece of glass over it, almost flush with the LED, and have an internal bezel hold it in place (as to not increase the external diameter).

Once that tube is waterproof, pop the head back on. Still zoomable.

Or do it backwards. Start with an S2+ as if you’re making a triple. No reflector, no TIR lens, nothing, just a thin ring around the inside of the tube to keep the LED from being squished against the front glass when the pill’s snugged up. (If you’ve ever seen an aspheric kit for a drop-in, you’ll know what I mean.) And the ring would press on the glass around the periphery, just as a reflector would, smooshing the glass up against the sealing O-ring.

So now you got an S2+ as a mule, with a domeless LED (or HI version vs HD, whatever), that’s 1mm or less from the front glass. It’s as watertight as all get-out.

Now you pull the head from an SK98, or G700, or whatever might fit over the S2+, and use that somehow.

Of course, you’d be finagling whatever you got to try to make the tube and head fit together, whether O-rings or whatnot. Point being that no matter how much water got into the head (ideally none at all, but it wouldn’t be catastrophic if some did), the tube itself, with switch, LED, battery, and driver, stays happily dry and waterproof.

Maybe I described it wrong but it seems exactly what I meant. :slight_smile:
I adjusted the description, please tell me if it’s more understandable.

Argo I think you and Lightbringer are on the right path. I can see in my head what you both are talking about. I imagine the difficult part would be finding the right parts that fit together. I am no zoomie guru. I have a handful of single mode SK68’s for the kids when they are running around outside and the Wowtacs A3 and A3S, which I use. The A3 is under construction right now. The Wowtacs are IPX4 rated, which I believe means they are two drops of water resistant. I do notice that when working the zoom, it will get stiff as you are moving back down from full zoom. Opening the tail cap for the air to escape makes it much easier so it may be a bit more water resistant than they claim. I still wouldn’t even use it in the rain.

One of the SK68’s has a SST-20 and a convoy biscotti driver in it. I fixed the lens and tube to full flood. One of my favorite lights. Since it’s fixed I should be able to get it water proof with little work. Keeping a moving object waterproof in a flashlight seems like it’s going to take a little work. I’ll keep up with the thread and see what happens.

Here’s a pretty interesting zoomie….that’s a DIVE light. Not sure if this is what you’re shooting for, but here ya go!


It has a reflector rather than a lens, so it’s very unlikely to be a zoomie. And I don’t see a zoom mentioned in the description…