Installing Underwater Illumination

The demand for outdoor living enhancements is growing every year. Water features are popular additions to outdoor living spaces. Lighting these features can be challenging — yet rewarding.

The most common way contractors illuminate water is by using a submersible fixture. Low-voltage underwater fixtures come in several different varieties. Adjustable projection-style fixtures are designed with integrated light sources or a drop-in lamp such as an MR16, MR11, or PAR36. Omnidirectional-style fixtures use miniature drop-in lamps, such as a G4 bi-pin, single contact bayonet, or a built-in LED light source. Both styles of fixtures usually come with a weighted base and a two or three-conductor SO-style cable.

Adjustable projection-style fixtures are very effective when illuminating a waterfall or the underside of a tiered fountain. These fixtures can also be used to illuminate the water flow in a stream. Illuminated moving water creates a dramatic effect on any surrounding architecture or plant material on a property.

Omnidirectional fixtures can be used underneath a waterfall to create a backlighting effect. When placed in the bottom of a pond, an omnidirectional fixture can provide soft, even illumination. Depending on the viewing angle, this type of fixture may need to be shielded with underwater plants or flat rocks.

When selecting an underwater fixture, be aware of the clarity and depth of the body of water. A murky pond will not look any better with a light in it. If the water is deep, you may need to use a brighter lamp or a narrow beam angle to project the light through the depth of the water.

Many mistakes can occur when installing a low voltage underwater fixture. The most common is in the cable connection.

  • Round SO cable is normally used on most submersible lighting fixtures. This is a multi-conductor style cable that contains fiber spacers between the conductors.
  • Proper sealing of the cable ends is very important. The fiber spacers can act as a wick and allow water to be drawn into the fixture.
  • A best practice is to ensure the connections are made away from the water and in a dry junction box.
  • If the fixture must be spliced underwater, use a UL-approved submersible junction box or epoxy filled cable connector.

Always be sure the transformer used on a project is approved for underwater lights; confirm this on the manufacturers’ website. When servicing an underwater fixture, it is critical to change the seal every time you service the fixture.

And finally, be sure to read all the specifications on the chosen underwater lighting fixture. Many of these fixtures are not made for “people water,” like swimming pool waterfalls or splash pads. Check with a local electrical inspector for any special requirements pertaining to the installation of underwater fixtures. Inspectors may require that fixtures be bonded to the control panel, even though the fixtures are low voltage.

The effects of underwater lighting can be quite stunning. Follow these guidelines and keep it safe and beautiful!


Article provided by Brilliance LED, a manufacturer of high-performance landscape retrofit lamps serving both commercial and residential markets, and a leader in the LED and Green Industry. For more information and design tips, visit

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