Transformers for Pond Lights

When it comes to pond lights, we want to be very careful.

We're putting electricity into water and if that doesn't come with a slight risk, then I don't know what does.

If you constructed your pond as per suggestions, you've had a licensed electrician run the power lines to your pump area. This is a good start.

And that person has also installed ground fault interrupter boxes that will instantly kill the power if it detects any moisture in the circuit.

This is good.


Because now what you're going to be doing is stepping that 120 volt power over to a transformer that will lower the voltage to 12v. The wattage will depend on the transformer you pick.

The higher the wattage, the more lights and 12v accessories you can run.

Measuring Lighting Load

A gentle reminder from grade 12 physics to help you figure out which unit of measurement you can use to determine your lighting load. :-)

Volts x amps = watts. Or amps equals watts divided by volts

This means your voltage is always the same at 12v. If you total up your wattage needs, and the transformer is sold by amperage, you can figure out the amps needed.

Ten 15-watt lightbulbs will require 150 watts divided by 12 so a 12.5 amp transformer will do the job. In practical terms though - always buy bigger than you need.

Reverse Engineer

This is why it is better to reverse engineer the entire pond lighting system before you go out to buy the stuff. If you know you want 10 light fixtures in your garden area and you know that each one of those fixtures needs 15 or 5 lights of 100 watts each, you'll be able to figure out the amperage needed to run the system.

In practical terms, total the wattage of all the light bulbs, throw in a few extra light bulbs for good measure and then always buy upwards of your requirements.

You might have to spend a few extra bucks but in the long run, you'll only buy one of the 100 amp systems while you might have to wind up buying 2 of the 50 amp systems to handle the next garden pond light project you want. Because you'll only need one transformer to handle the pond as well as the garden lighting. (Once your better half sees pond lighting, be prepared to install garden lighting.)

Always Buy Certified

I know I don't have to tell you this but I will anyway. Always buy safety certified pond rated equipment. Even 12 volts out of place can kill your fish pretty quickly.

Extra Wire

And when you're laying your pond lights into place, leave two or three feet of wire at the fixture that will be long enough to lift the pond light fixture totally clear of the water.

Changing light bulbs (yes, they blow out) is so much easier when you can lift the fixture clear of the water to change the bulb. Doing it underwater or draining the water out to change a light bulb is a royal pain in the anatomy.

Did I mention that you unplug the transformer whenever you have to do this?!!

The specific pond lights you use and how you design your night lighting system is a subject for another page. But get that transformer right and you'll be well and truly on your way to happiness with pond lights.

Shopping Resources for this Article

This is an example of a programmable 60-watt (4 light) transformer