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Pool and Spa Lighting

How To Change Or Replace Underwater Lights and Bulbs For Swimming Pools And Hot Tub Spas


Lighting is essential if the pool is to be used at night. External lighting of your pool, spa, or water feature is possible with a variety of high- and low-voltage systems. For installation and maintenance of external systems, it is recommended you consult your local electrician. For lighting the water from within, however, there are also a variety of options. This is where the water technician needs to be an expert.

Figure 15 shows a typical pool or spa light housed in a stainless steel conical shaped fixture, about 8 inches in diameter by 6 to 10 inches deep. The fixture is mounted in the wall of the pool or spa in a container called a niche.

Like the lights in your house, pool and spa light fixtures have a standard, screw-in socket for a bulb (in fact, your household 100-watt bulb will work in a 120-volt pool or spa fixture). The cord that supplies electricity to the fixture is waterproof and enters the unit through a waterproof seal. There are no user serviceable parts in the cord, seal, or fixture except for changing the bulb. Although the correct term is lamp, will use the more common expression bulb. Fixtures and bulbs are available in 120 or 240 volts, but 120 volts is most common for residential use. Bulbs generally run from 300 to 500 watts.

Fixtures are sold with cords of 10 to 100 feet, so you need to know the distance from the light niche to the junction box to determine what you need when purchasing a replacement fixture. A simple rule of thumb is to buy the next longer length than you think you need, because you can always use the cord for something else and the few extra bucks is cheaper than getting one a little too short and making another trip to the supply house.

Smaller versions of these fixtures are available for spas. They come in 120 or 240 volts, but usually employ smaller-based specialty bulbs that might screw in or have bayonet-type sockets. A quartz or halogen bulb will give you the most light from a small low-wattage bulb. These new technology bulbs are very expensive but save energy and need replacement less often than hotter, higher wattage standard bulbs.

You might encounter very old fixtures that are basically designed the same as modern ones, but they have a mogul base. The socket for these are also female threaded, but they are about twice the diameter to accommodate bulbs with that mogul-style base. Replacement bulbs are still available for these fixtures.

Light fixtures are sealed to be completely watertight, so the air inside reaches extreme temperatures unless it is cooled by contact with the water. Never turn these lights on if there is no water in the pool.

Most fixtures have lens overlays available in a variety of colors. These are plastic lenses that snap over the glass lenses to make the light blue, green, or whatever color. Being very thin plastic, these too will quickly melt if the light is operated out of the water.

Fixtures are held in the wall of the pool or spa in a light niche. A niche is a metal can large enough to contain the fixture, cemented watertight to the side of the pool. A waterproof conduit leads away from the niche to above the water level out of the ground to a junction box.


Installation of new lighting needs following;

  1. Access to the electrical connection
  2. Fuse
  3. Sockets
  4. Light fixture
  5. Light bulb

Pool lights require fixtures that have a standard, screw in socket, just like a normal household bulb. A water proof cord supplies electricity to the fixture, and enters through a water proof seal. The only serviceable part inside the fixture is the light bulb. Fixtures and bulbs come in 120 or 240 volts. 120 volts are the most common for residential use. If the fixture becomes rusted or otherwise damaged, it cannot be fixed. The entire fixture has to be replaced.

Electrical work must be perfect and in accordance to local, state and national codes. Codes may vary from state to state. Be sure to hire a competent licensed electrician to complete the work needed.

Since you probably won't be installing too many light niches on new pools, will outline in next section the procedure for replacing a fixture when it rusts out or otherwise fails.

Replacing a Fixture

Fixtures come with attached, water proof cords of 10 to 100 feet. Know the distance from the light niche to the junction box before you purchase a replacement fixture. Buy a longer cord than you think necessary and cut it to fit. As with all electrical repairs, turn off the power to the fixture at the circuit breaker and tape over it so no one turns it back on while you are working.

The steps involved are:

  1. Disconnecting the Wiring
  2. Removing the Old Fixture
  3. Cutting of the Old Fixture
  4. Preparing the New Fixture
  5. Pulling the New Cord
  6. Installing the New Fixture

Subsequent sections describes above steps to replace a fixture.

Disconnecting the Wiring

Turn off the power source at the breaker. Find the junction box. On older pools, this will be in the deck directly above the light niche, often under a 4-inch diameter stainless steel (or bronze) cover plate that is held in place by three screws that probably have rusted or stripped heads, making them impossible to remove.

Later building codes required the junction box to be at least 5 feet from the edge of the water and 18 inches above the surface of the water, so on more recently constructed pools, look in the garden directly behind the light niche and you will often find it sticking up there.

A typical junction box (simply called a J-box). Remove the four screws and take off the cover. Three wires come into the box from the breaker or switch and three go out of the box to the light fixture. The three to the light fixture will be individually insulated, colored white, black, and green, and are bound together with a single rubber sheath that waterproofs the package. This is the cord of the light fixture as described previously. Disconnect the three wires. Unscrew the cord clamp.

Removing the Old Fixture

Lean into the pool and remove the face rim lock-screw (retaining screw) from the faceplate that holds the fixture to the niche. The top of the fixture will float outward, the bottom is hooked into the niche and can be lifted out.

Uncoil the excess cord to give you enough slack to raise the fixture out of the water onto the deck. Go back to your j-box and tug at the cord of the fixture. If you see the cord move at the fixture end, you know the replacement is an easy one. If it's tight, follow the steps outlined later (see tight cords).

Cutting off the Old Fixture

Cut the cord where it enters the old fixture. Strip off the rubber sheath, back about 6 inches. Remove the string or paper threads that run alongside the wires (these were put in the cord to add strength for when you pull on it). Remove the insulation from each single wire back about 6 inches.

Preparing the New Fixture

Remove the new fixture from the box and float it in the pool. Take the wires of the new fixture and strip the cord back as described in next section. Now bind the wires of the new cord to the ones of the old, folding each wire over as if to make a hook, then connecting the two (like two fishing hooks) and twisting the loose end around the base wire. Use electrical tape to cover the exposed wire, wrapping it tightly and thoroughly.

Don't tape so much that you make a connection thicker than the cord itself. It won't pass through the conduit easily. The idea is to make a union of the wires that will not separate when you pull.

Lay the cord out freely into the water. Pull the old cord at the J-box until you have pulled the connection and the new cord through. Some niches have the conduit connector in the top of the niche pointing upward at an angle, so when pulling the cord, it might snag at your connection.

To solve this problem, have someone lean into the pool and angle the cable down into the water, at the same angle as the conduit connector itself. That person can feed the line as you pull from the other end. Keep pulling until you have enough cord left with the fixture for it to easily reach up to the deck for future bulb-changing access. Now untape your connection and remove the old wire.

Pulling the New Cord

If the cord won't budge from either direction, the cord might have swelled from age, heat (electricity creates heat), or moisture. Try pouring tile soap down the conduit from the J-box. You might have to let it sit overnight to slither all the way along the conduit and be effective. Some service technicians use oil, but whatever you use will eventually end up in the pool.

Another trick is to use leverage. Place a long 2-by-4-inch board down into the pool and run the cord up along its length. Using the edge of the pool coping as a fulcrum, try to pry the cord away from the fixture or get your local electrician to help you with his wire pulling levers. Another trick is to cut the cord as low as possible at the J-box side of the conduit. Using your drain flush (blow bag) and the garden hose, try forcing water from the J-box to the pool through the conduit to loosen the cord. Compressed air might also work. Be careful not to exert too much pressure with these techniques, however, because you might crack the conduit, which might be brittle PVC or thin, rusting copper.

Sometimes the cable comes out, but the new one tears off as you are pulling it. Remove the new cord and use an electrician's snake to run through the conduit, starting at the J-box and working toward the pool. When it comes out the other end, hook the wires of the new fixture to it and try to pull them through again.

Installing the New Fixture

Reach into the pool again and coil the excess line around the fixture, then reset the fixture in the niche. Replace the lock-screw on top.

Sometimes, particularly if the fixture is way below the waterline, you might have to get into the pool to loosen or reset the fixture. If you're on the deck and having trouble lining up the face rim lock-screw with the hole of the niche, use a piece of coat hanger wire. Slide it through the hole on the faceplate and into the hole of the niche. Slide the fixture into place and the holes will line up for the screw. Remove the wire and insert the screw. Cut off any excess cord at the J-box, leaving enough to make a good connection with the supply wires. Reconnect the wiring and close the J-box. Test the fixture.

Replacing the Bulb

The most important factor in bulb replacement is to maintain the waterproof integrity of the fixture. Follow each step carefully to avoid leaks that will not only damage the new bulb and fixture, but might also lead to electrical shock of the next swimmer.

  1. Turn off the power, then get the fixture up on the deck as described previously.
  2. Remove the lens that is held in place by a clamp or a set of screws. Gently pry the lens away from the fixture, taking care not to gouge the lens gasket.
  3. Replace the bulb. Inside some fixtures you will find a bare coiled spring wire. This is non-electrical but is designed to break a circuit. Notice that without a bulb in place, the spring lays to one side of the fixture. Hold it up against the opposite side and screw in the new bulb. The spring lays on the bulb itself. If the bulb bursts when in use, the spring sweeps across the filament, cutting the electricity in the circuit. In this way, if water has gotten into the fixture, a live electrical circuit won't stay in contact with the water, ultimately electrocuting someone in the pool.
  4. Now place the fixture on the deck and turn on the light to make sure your new bulb works. Never operate a closed fixture out of the water, but with the lens off, the heat can escape without problem.
  5. Reassemble the fixture. Check you may need a new gasket. After long use, heat, and harsh chemicals, the old one is probably compressed, and if it doesn't fail immediately, it might fail before the next bulb change.
  6. In reassembling the faceplate, if it has the series of screws, tighten them on opposite sides until you have done them all. This applies even pressure and prevents gaps in the gasket that will ultimately leak.
  7. Lay the fixture back in the water. Hold it underwater for several minutes to make sure it doesn't leak. A few bubbles might rise from air trapped under the lip of the faceplate, but a steady stream means the fixture is filling with water. Take it apart again and dry it thoroughly. Go back to step 4 and be more careful.
  8. If it passes the leak test, turn it on for a few seconds before putting the fixture back in the niche. During reassembly or testing you might have banged the unit around enough to break the bulb or its delicate filament, or you might have a bad bulb. Remember, the closed fixture depends on water for cooling, so conduct this test for literally no more than two seconds. Now reset the fixture in the niche as outlined previously.

The steps involved are

  1. Disassembling the Fixture
  2. Replacing the Bulb
  3. Reassembling the Fixture

Subsequent sections describes this process in detail.

Disassembling the Fixture

To remove the lens clamp, loosen the screws that hold it in place. Gently pry the lens from the fixture. Do on gouge the lens gasket.

Replace the Bulb

Unscrew the old bulb, and screw in the new one. Some fixtures contain a bare-coiled spring wire. It is not wired to the electrical current and is designed to break the circuit. If the bulb breaks while in use, the spring sweeps across the filament, cutting the electricity in the circuit. This safety item ensures that if water does get into the fixture, the next swimmer does not get electrocuted.

Before reassembling the fixture, place it on the deck and briefly turn on the light to make sure it works. Normally a closed fixture is not turned on while out of the water. With the lens off, however, the heat can escape.

Reassembling the Fixture

To reassemble the fixture, simply reverse the procedure described in previous sections. In addition, replace the gasket. An old gasket has been exposed to months of chemicals, heat, and compression. Place the new gasket around the lens as if it were a rubber band stretched around a drinking glass. If the faceplate screws into place, tighten the screws on opposite sides to apply even pressure on the gasket and avoid gaps which later cause leaks. Replace the fixture in the niche as described in Replacing a fixture section.

Low Voltage Lights

Designed like their 120/240-volt cousins, low-voltage fixtures employ a transformer to drop the voltage to 24 volts. As a result, the highest wattage fixture does not deliver much light, so they are used in spas or fountains where lower wattage is sufficient to light a smaller area. Installation, repair, and replacement techniques are identical to those described previously.


The recent development in water lighting is the use of fiberoptics. The hardware looks the same, but instead of running electricity to a fixture, the cord in the conduit contains thin plastic fibers that conduct light, not electricity. They terminate in a lens in the water to shed the light into the pool or spa. The light source and electricity are located safely away from the body of water. Most of these are used in smaller bodies of water because manufacturers have not yet developed fiberoptics with enough power to light large pools. The manufacturers are working towards development of the fiber optics light for large pools. Troubleshooting and maintenance of low-voltage and fiberoptic systems are similar to those described previously.


Electricity and water mix only too well, often with deadly results. Therefore, since you can be injured or your work might make you liable for someone else's injury, so be careful when you are working on installing or replacing lights.

  • If a fixture, lens, or gasket looks suspicious, replace it. It's not worth the time, hazard, or money.
  • Use the bulb, gasket, or replacement lens that fits the fixture. Try to get the same manufacturer's replacement parts or use the generic brand designed for that make and model. You might be able to force a bulb, gasket, or lens into place and it might stay watertight for a few days, but what happens when it ultimately overheats and leaks, bringing water, swimmer, and electricity into contact?
  • Stubby bulbs are popular replacements. They are squat, short bulbs so they fit almost any fixture. The problem is that by being short, the heat is brought closer to the end of the fixture than the originally designed long-stem bulb. Also, bulbs with a reflector material painted on the underside of the bulb will reflect more light into the pool, so you get the appearance of a higher wattage bulb. The reflective surface is also designed to direct heat away from the rear of the fixture. This is significant because the resin at the rear of the fixture, that makes it waterproof, can melt.

For the same reason, don't put higher wattage bulbs in a fixture than it was designed to take. If it isn't marked and you can't read the old bulb, don't use greater than 400 watts in your replacement.

When changing a bulb, as with any repair, you are required to work to local building and health department codes. This might mean bringing an older installation up to code by adding a ground fault interrupter (GFCI).


Replacing a bulb or fixture as outlined previously is about all you will need to do with lights and water. But how do you know if it's the bulb, cord, fixture, or breaker? if the light won't come on, try this procedure.

  1. Make a visual inspection. Look at the lens of the fixture (remove any color overlays first). If you can see water or black soot (the result of a bulb bursting in the fixture), you know it will have to come apart. If the water has filled the fixture, it might only look cloudy, so it pays to know what a dry, well-operating fixture looks like underwater.
  2. Turn off the power supply at the circuit breaker. Open the J-box and expose the wiring connections. On old J-boxes mounted in the deck, the gasket often fails and allows water to fill the box. The water shorts out the wiring. Clean and dry out the box and replace the gasket and lid firmly.
  3. If that is not the obvious problem, turn the breaker and light switch on and use your multimeter to verify that power is getting to the light fixture cord. if not, trace back the problem to the breaker or switch. Sometimes there is more than one switch, such as a remote control, and the problem might just be a second switch being off.
  4. If the breaker trips off when you turn on the light, disconnect the light cord from the power wiring at the J-box and reset the breaker. If it still trips off, the problem is the breaker or GFCI, or more rarely, the wires between the breaker and J-box have shorted together. If the breaker stays on, the problem is in the fixture or its wiring.
  5. Set your multimeter to test circuit continuity. Touch one lead to the white wire of the fixture cord and one to the black. If you have continuity, the bulb and wiring are good.
  6. Touch one lead to the green and the other to the white, then the black. If continuity exists between white and green or black and green, the wiring is bad. You can test bulbs that way too-touch one lead to the threaded part of the bulb base and one lead to the tip of the base. A good bulb will have a complete circuit (continuity), a bad one will not.


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