LOW-VOLTAGE LIGHTING

By Constantine Pergantis, Nite Lites, North Potomac, MD

Question 1: Installing lights in trees and on buildings

Question 2: Charging for fixtures

Question 3: The circuit breakers on low voltage system keep tripping

Question 4: Lamp size relation to light intensity

Question 5: Basic types of lamps

Question 6: What is the difference between lamps for enclosed and open fixtures?


Question 1: Is the extra difficulty of installing lights in trees and on buildings to shine down upon a landscape worth the effort?

Pergantis. Ask anyone with a pulse and they will have an opinion on what effect is better, uplighting or downlighting. Let's compare uplighting and downlighting and you be the judge.

The first major benefit of downlighting, that is locating the fixture above the landscape in a tree, eave or on a pole, is the light beam illuminates a larger area. Light shines through the branches and leaves of plants casting interesting shadows onto the ground. This technique is commonly called moonlighting.

Because the fixtures are out of reach, vandalism is greatly reduced. Once the lights are set, little repair or adjustment is needed.

On the down side, more cable is needed. As a result, the amount of voltage reaching the lamp is slightly less. To compensate for lower voltage, increase the size of the wire.

Keep in mind that trees are constantly growing. Leave some slack in the cable and use an adjustable lag bolt to secure the mounting hardware. Also, do not hammer tacks all the way into the tree to secure the cable. The tree will grow over the cable and tacks with time.

Since downlighting can be used for spotlighting or cross lighting, plant growth can impact both the angle of the beam and any foliage blocking it. Downlighting resembles natural light due to its origin.

Uplighting is easier to accomplish, however it is rarely seen in nature. It gives a slightly mysterious appearance which demands attention. Uplighting illuminates the bark, innerworkings of the branch structure, and the under-sides of the leaves.

Maintenance of ground fixtures is easier, however debris can fall on top of the lamp and vandalism is more likely. You will need less cable during installation and will have the benefit of more voltage and brightness.

Fixtures are generally well-type or accent floods. Since these fixtures are within reach of any curious bystander, the threat of shock is important. Low-voltage lamps for uplighting eliminate this threat.

As you can see, there is no clear winner between uplighting and downlighting. They both have their own special place in an effective lighting design. Professional lighting contractors should be skilled at installing and maintaining both types of lighting.


Question 2: My first-time lighting customers are sometimes shocked when they see what I charge for fixtures. They say I charge as much for one fixture as they could pay for an entire prepackaged kit in discount stores. How do you deal with this problem?

Pergantis: Prepackaged kits typically have low wattages and very short cable runs. When they are installed along sidewalks or paths they end up looking like miniature runways. The kits contain a single type of fixture, usually constructed of black plastic. They provide very limited design flexibility and require more maintenance than professional fixtures.

A professional lighting contractor uses a variety of fixtures made of durable materials and installs them so they will be low maintenance. The appearance of professional fixtures during the day is much richer. A wider range of lamps can be used in professional fixtures to make the night landscape more dramatic.

The bottom end of the spectrum are the prepackaged plastic kits. The next step up is steel. They are more durable, but will eventually rust and cause more problems than they are worth.

The minimal increase in cost to upgrade to aluminum is worth the benefit in quality. For the past few years, manufacturers have been getting away from steel and producing aluminum fixtures.

There are two types of manufacturing methods used to produce aluminum fixtures. Spinnings are the least expensive because the dies are cheaper to make and there is less material involved in the final product. Spinnings give you that tinny feeling and are very light.

Castings are more expensive, but the overall weight and sturdiness of the fixture give the appearance of a high quality product. You will be able to command more money with cast aluminum fixtures.

Copper, brass and bronze fixtures are the top of the line in cost and quality. Steel rusts and aluminum oxidizes in harsh environments. That is why copper, brass and bronze fixtures are found mainly in coastal areas. Copper, brass and bronze change color in a natural weathering process. Many people like this weathered appearance. Aluminum fixtures can be painted to resemble weathered fixtures.

A big justification for quality fixtures is the construction of the interior parts, such as brass sockets and mounting brackets. Manufacturers are starting to use PVC and similar composites for the parts of the fixture that contact the soil.


Question 3: The circuit breakers on my low voltage system keep tripping. For some reason I can't seem to locate the problem. I've checked switches, wiring, lamps, and the transformer. They've all checked out, but the problem persists. I'm at a loss.

Pergantis: Low voltage systems are safe and relatively simple to install and maintain. However, during installation and after a few years of use, there are a few trouble-shooting questions that invariably come up.

A problem that frequently occurs is tripping of circuit breakers. On a single circuit system, if the breaker trips immediately (after power is turned on), the problem is either a nick in the wire, the pins in a connector are touching, or there is a bad lamp socket. If it takes a few minutes for the circuit breaker to trip after the switch is thrown, the transformer is probably overloading. In this case, you need to get a larger transformer, eliminate a fixture or two, or lower the wattage of some of the fixtures.

Another common problem is that the lights will be on, but will be very dim. Usually, this is caused by too many fixtures or too much wattage demand on the transformer. Another possible cause is that the cable run is too long, causing too much resistance; or the cable gauge is too small and unable to carry the load. Rarely checked, but very important, is the line voltage outlet. If you are not receiving 120 volts on the primary side, then the transformer will not produce 12 volts on the secondary side.

On a two-circuit system, if you have more than one cable attached to the transformer and are making a loop, be sure to have the "ribbed" or "lettered" sides of the cable together, the middle wires together, and the smooth sides together, otherwise the polarity will be out of balance and the circuit breaker will trip. If only half your lights are out and the circuit breaker has not tripped, it probably means the switch on the transformer is bad; probably due to a burned up or broken wire inside. The solution is to get a new switch and wire or bypass the bad switch directly to the primary (the switch is merely a convenience).

Here are some preventive maintenance tips you can use to minimize the need for trouble-shooting. Use clear silicon on transformer screw terminals and lamp sockets to reduce corrosion (this makes it easier to remove lamps without breaking them). Try to keep transformers at least 12 inches above the ground to keep out insects and debris that splash up when it rains.


Question 4: How does lamp size relate to light intensity?

Pergantis. Because low-voltage lamps have smaller filaments, they produce a more controlled beam spread and a high main beam lumen output. More focused distribution of the light output enables smaller filaments to appear to have the same intensity as larger lamps. As a result, the smaller lamps can be used in designing smaller fixtures.


Question 5: What are some basic types of lamps?

Pergantis: One of the most commonly used lamps is the single contact S8. It resembles a car tail light lamp and is used for most path/area type fixtures. The S8 is available in five wattages and lasts 1,000 hours.

The T3 bi-pin halogen lamp is beginning to replace the S8 because of its 3,000 hour lamp life and color of the light beam. It is also generates more lumens per watt of electricity.

MR16s and MR1s are widely used because of their size and punch. They resemble a projector lamp and are available in seven wattages and six beam spreads per wattage.


Question 6: What is the difference between lamps for enclosed and open fixtures?

Pergantis: Most early low-voltage lamps could not get wet and could be used only in enclosed fixtures. New lamps that resemble auto headlights and don't require an enclosed fixture are available for low-voltage systems.

One example is the PAR36 lamp that comes in seven different wattages and four beam spreads. Both General Electric and Osram Sylvania are now producing halogen PAR36 lamps. The life of halogen lamps is twice that of traditional models, up to 4,000 hours. The center beam candlepower of the Osram Sylvania 36 watt halogen lamp is actually greater than the 50 watt standard PAR36. Using the 36 watt lamp instead of the 50 watt lamp allows you to install more fixtures on your transformer.

There are many other lamps to use in your designs. They include PARs, As, Rs, ALRs and wedge-base lamps. Low-voltage PL fluorescent fixtures are also available from 5 to 13 watts. However, like indoor fluorescent fixtures, they require a ballast to operate at 12-volts.

Visit your low voltage lighting supplier to get the latest on lamps. You might be able to use fixtures with lower wattage than before. That measures more fixtures per transformer and more design flexibility.



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