Introduction: Underwater Lights - Insulated in Old Jam Jars

By Christian Liljedahl
About: I am creating interactive installations and performances. Inviting the spectator to participate in various ways I use any media possible to bring "the idea" to life. Electronics, computers, wood, rope, water…

At the art ship Illutron we often use lights under water. For illumination and decoration. It is a beautiful effect, and it gives a touch of magic to performances on water.

Leave the lights on for a few hours, and millions of little fish will be attracted and circle the lights.

I recently went to Linz to the art ship Eleonore. I did an underwater light workshop, and that resulted in the images here.

It is really very easy and takes about ½ hour to make

  • Stick a light bulb in a jar
  • Run the cable through the lid using a cable gland
  • Fill the jar with cooking oil and close it
  • Dump it in the water and... Lights!!

Materials

  • A jam jar (any jar with a big lid and large enough to hold a light bulb)
  • A cable gland
  • Light bulb with socket
    • Any type is fine. LED, compact fluorescent or classic. But you want as much power as you can get.
  • Cooking oil

Tools

  • A step drill (unibit)

Skills

  • How to mount light bulb sockets and plugs on a cable

Step 1: Drill a Hole and Mount a Cable Gland

Drill a hole in the lid using a step drill / unibit.

If you don't have a step drill, buy one. You can use other types of drill to make the hole, but because the metal of the lid are so thin, it is not easy to make a nice hole without the metal ripping.

Smooth the edges of the hole with a file.

Mount the cable gland

Stick it through the hole in the lid and tighten the plastic nut on the back side.

If you, like us, did a poor job drilling a nice hole you might want to add a rubber gasket on each side of the lid to make a better seal.

A piece of old bicycle tube makes an excellent gasket

Electricity and water

Around now, you are probably wondering if it is safe to use 230 V electricity under water. As long as everything is properly sealed and insulated from getting in touch with water, all is good.

Getting a jam jar and a cable gland water tight against pressure can be difficult. If we just had air in the jar, water would easily be able to squeeze in and flood the jar because air is compressible.

We fill the jar with cooking oil (cooking oil is a very fine insulator) to make it impossible for any water to squeeze in. Cooking oil is incompressible, and, since we place the jam jar upside down, should a little drop of water come in, it will stay around the gland and not get up to the electric wires, because oil is less dense than water.

  • If you don't feel confident with using 230 V this method works just as fine for 12 V bulbs.
  • Make sure your power outlet is protected by a

    GFCI (Ground Fault Circuit Interrupter). In some contries, a GFCI are mandatory on all installations, but if this is not the case where you live, consider getting an inline GFCI. Thanks

    user Scarecreaux for pointing this out to me.

Step 2: Mount the Socket and a Plug and Fill the Jar With Cooking Oil

Run a piece of cable through the cable gland.

  • Use at least 20 meters of cable, to have more freedom of placement.
  • If in doubt, use a longer cable. You can always make it shorter.

Mount a light bulb socket on the inside, and a plug on the outside.

  • Do this as you normally would do.
  • If you don't know how to mount sockets and plugs, get someone to show you. It's easy.

Fill it and close it up

  • Fill the jar with cooking oil
  • Close the lid
  • Tighten the cable gland around the cable.

We use cooking oil, but any oil could do. Cooking oil is just more eco-friendly and harmless to the environment, should you spill a drop.

Mount the jar upside down

Make sure you get the jam jar hanging upside down. We just used a couple of zip-ties around the jar.

We want the jam jar upside down to keep the oil inside, if the seal at the lid or cable glad leaks a little. Oil floats on water and will stay at the top and not escape.

Step 3: Test the Light and Dump It in the Sea

Make sure all is working.

I suggest trying the lights in a bucket first. This will also rinse of any excess oil.

Then find some nice places around your boat or whatever you have on water to place the lights.

Don't sink them too deep. 1-2 meter is fine. The water dims the light a lot, and the lights will look quite puny at 8-10 meters depth.

Variations

There are a lot of possibilities for variations and combinations. RGB-leds with color control. Placing many lights over a larger area etc.

All these experiments are easily done, because this method is so quick to assemble and reassemble.

Photos

Most of the photos here where taken by Rosa Angora during a workshop I did at the art ship Eleonore in Linz, Austria in late 2014.

Photos from Illutron in Copenhagen are by Mathias Vejerslev

Step 4: Update: Halogen Tube in an Old PET Bottle

If you want immense power on the light, you need something like a halogen tube.

Trouble with halogen tubes is, that they burn so bright, that they easily overheat and die.

And, handling is difficult, if you touch them, the sodium from the salt-sweat on your hands will destroy the crystal glass at temperature. Same goes for salt water, obviously.

But, the oily trick works for these too!

  • Solder wire to the ends of the tube
  • Stick the tube in an old plastic bottle
  • Run the cable through the cap using a cable gland
  • Fill with cooking oil

Will the solder not melt in the heat?

  • Yes it will! - and that's good.
    • If the oil for some reason does not cool properly, the tube will heat up, the solder will melt, and the wire will fall of. Built in thermal fuse.

So far I have tried a 250 W tube in a 500 mL bottle. That worked fine.

A 1000 W tube in a 1000 mL bottle overheated. Probably needs a 1.5 L bottle to have enough circulation and cooling inside from the oil.