June 18, 2012

All lamps (incandescent or LED) start to degrade the second they are turned on; some lamps are engineered to live longer than others and their price points typically reflect their robustness and longevity. (LED = Light Emitting Diode). For incandescent lamps, “average life” (usually written in the specs or on the box) is determined in a decidedly unscientific manner. Usually 100 lamps are installed in sockets on a large board, and when 50% of the lamps have burned out, that sets “average life.” Units 1 – 49 clearly failed beforehand, while units 51 – 100 could operate significantly longer. Longevity has a lot to do with the lamps’ manufacturing processes, the quality of materials used, and certainly the environment in which they’re operating. There are conditions that cause lamps to die before their average life span is reached.. Anyone who installs and maintains lighting systems will benefit by understanding what affects lamp life.

Over-Volted

If the voltage supplied is below or above the designated voltage range for a particular lamp, then its life will likely be compromised. (Over volting is typically worse than under volting.) Operating voltages over 12 volts are common in landscape lighting systems and this is a leading cause of premature lamp death. This occurs when installers don’t use a volt meter to confirm the voltage on each run. Electricity supply can fluctuate so it’s important to understand that and compensate for it in the design.

Over-volted lamps can be caused by several factors. Using the wrong voltage tap, not replacing burned out incandescent lamps (Thus causing voltage to increase at remaining lamps which in turn causes them to burn out. This is called “cascading failure”), or higher-than-normal voltage on the primary (120V) side can be factors. Essentially a low voltage lighting transformer doesn’t magically produce 12 volts at the 12 volt tap. What it does do is reduce the voltage from primary to secondary at a 10:1 ratio. So if the primary voltage is at 120V, then in theory the 12V tap should have 12 volts. There are mechanical inefficiencies in all equipment so voltage could be gained or lost just in the copper windings inside the transformer. Thus you might get 11.8 volts or 12.3 volts. It all depends on the primary voltage and the efficiency of the transformer itself. The only way for an installer to measure the voltage is by using a volt meter. Poor system layout is a common flaw resulting in lamps being over volted. Care must be given to insure wire paths and wire gauges are suitable to deliver the desired voltage to each fixture. Everything electrical has a limit, and if those limits are exceeded then wire can overheat, melt, trip breakers, cause lamp failure, etc.

A volt meter, amp meter, or multi-meter (measures both voltage and amperage) is essential to properly install a low voltage lighting system. Without it you have no idea how much voltage is being supplied at a fixture.

(Cascading Failure explained: Instruct property owners to call for service when they notice a burned out incandescent lamp. Otherwise, teach them how to replace lamps themselves and sell them the correct lamps to use. Failure to replace burned out lamps in a timely manner means that all remaining lamps are now receiving more voltage since one or more burned out lamps aren’t using up their share. This could result in elevated voltage and faster failure of remaining lamps. Remind property owners not to touch lamps (the glass envelope which surrounds the filament) with bare skin as skin oil can concentrate heat at those points and compromise the lamp.)

Under-Volted

When voltage supplied is lower than 10.8 volts lifespan can be reduced. This can be caused by poor electrical supply, inappropriate wiring, selection of wrong/too small transformer type and/or selection of too small of a wire gauge.

Poor connections can also be the culprit. Make sure lamp bases and sockets/forks are in tight contact. Loose connections either don’t come on or they can cause arcing (see below). Apply silicone or di-electric grease liberally to all lamp bases and sockets/forks to protect them from moisture-causing corrosion and seizing.

(Ideal Lamp Voltage Explained: For any incandescent lamp the minimum voltage should be 10.8 volt and the maximum should be 12.0 volt. The ideal “sweet spot” is 11.0 to 11.5 volt.)

In-Rush Current

In-rush current may occur when power initially comes on and travels the length of wire, through a fixture’s wiring and comes into contact with a lamp’s filament. This initial burst of voltage can be elevated enough to break the filament.

Install a minimum of 20 feet of wire between a transformer and any given wire run’s first fixture so that in-rush current has a chance to dissipate before coming into contact with the filament.

Additionally, slightly under-volting a 12 volt incandescent lamp will allow more of a buffer to absorb small voltage fluctuations.

Load Impact

Voltage can vary based on season, time of day, day of the week, equipment efficiency (e.g. neighborhood transformers), and even the overall load on any given circuit. All of these parameters can fluctuate on the primary (120V) side, so as a result they will vary on the secondary (12V) side, too.

A transformer is a device that reduces voltage 10:1 (from 120V to 12V), it does not magically produce 12V at the 12V tap. The 120V supply and any fluctuations it experiences are directly passed through to the 12V side. This can affect lamp life.

(Maintenance Tip: Take all voltage and amperage meter readings with every lamp on. If a lamp is missing or broken then any reading taken will be incorrect since the loads of those lamps will not be included.)

Arcing

Spikes in voltage due to loose connections, damaged wire, etc. can create excessive heat and damage the filament and socket and lead to premature failure. Arcing can also melt connections and terminal blocks, too.

Fixture Quality

Poor quality sockets that don’t maintain contact with lamp bases can make a lamp fail.

(Maintenance Tip: Do not push the metal tips of a volt meter into any bi-pin socket. The tips are bigger than most lamp pins and they can damage the interior of the socket or widen it so that lamps only come in intermittent contact. This damages a socket and can lead to arcing between the lamp and socket. In addition, if a measurement is being taken at a fixture without a lamp in it, then the full load is not being measured.)

Low quality materials will burn and/or melt when a hot incandescent lamp comes too close to them. Cheap products are that way for a reason.

Bad Fixture Application

Using a fixture in an unintended or incorrect manner can compromise lamp life. Examples of this include:

When one installs a fixture without appropriate gaskets (poor sealing)
By installing a down-light as an up-light (water can get in)
Installing a well light too deeply in the ground can allow debris to enter the sleeve and cover the lamp thus trapping excessive heat or igniting mulch/pine straw.
When one installs a well light in clay soil without allowing for proper drainage (water accumulation)
Installing a path light right next to an irrigation spray head which allows water to spray under fixture hat and it could flood the socket compartment

Lamp Quality

When using poor quality lamps changes in ambient temperature and humidity can cause the interior reflective coating to fail. This results in the coating flaking off thus allowing light to escape out the back of the lamp. Also, uneven or poor pin placement can occur making the socket not match up to the pins. Poor quality filaments and poor seals can also be a result. This can cause air to seep in or specialty gases to leak out allowing the filament to burn up. Poor seals can also lead to moisture or water penetration which can crack or break a lamp or simply burn it out.

You always get what you pay for. Buying a cheap lamp guarantees less life.

(Halogen Explained: Filaments are usually made from Tungsten, a brittle metal. When drawn into a fine wire it becomes very delicate. Many filaments have carbon particles attached to them, and the specialty gases inside the glass envelope force the particles to re-attach as the filament burns thus making the filament and lamp last longer.)

Halogen (and other gases) perform this function by forcing the particles to re-attachto the filament through a process referred to as the “Halogen Regenerative Cycle.” This process works when the lamp receives voltage between 10.8 and 12.0. If you over or under volt a halogen lamp outside of this range, its life span can be reduced. Bottom line, use halogen lamps if you’re installing an incandescent system, otherwise use LED (Light Emitting Diode) to incorporate the longest lasting lamps possible (as compared to standard incandescent).

Excessive Vibration

Some lamps are subject to vibration or abrupt movement due to their mounting locations (near doors, in planting beds where sports balls can hit them, kicked by deer running through landscape beds, etc.), and this can compromise the filament and cause premature failure.

The vibration from rough handling of a fixture while its lamp is on can cause the filament to break. It’s not feasible to protect a fixture from every possible thing that can happen to it, but at least for installation it is best to install a fixture while it has no lamp. Lamps installed prior to mounting the fixture can be knocked loose from the socket and might not come on or may start arcing.

Water

Water contacting an exposed hot lamp can also cause a lamp to crack due to sudden, extreme temperature changes. (e.g. direct hit from irrigation spray). PAR36 lamps are built for direct exposure to the elements. They are able to handle normal exterior exposure, but it’s best to avoid large, direct hits of cold water while a lamp is turned on just to avoid this sort of thermal shock.

Wire Connections

A properly installed UL486D-listed connector (or equivalent) is also strongly recommended as these are the most robust, direct-bury connectors. These connectors have high quality silicone or di-electric grease in them and can protect the connection if properly installed.

A wire connector is a lighting system’s most vulnerable point, so using a high quality, robust connection is a good practice to establish, and it’s insurance against call-backs and system failures after a system is installed.

If moisture can get inside the wire jacket either through a knick in the jacket or a poorly installed wire connector, then the copper wire will start to corrode. This corrosion will impede electrical flow, thus increasing the voltage drop and decreasing the voltage at the lamp.

Lamp Field Testing

Set a Volt/Ohm meter to Continuity Test (so your hear a tone when a pathway exists). Touch the probes on both metal contacts on an incandescent lamp. If you hear a tone that means you have a complete circuit, thus a good lamp. If you hear nothing, then the filament is broken and the lamp is bad. This is handy to field test a lamp at any time whether you have electricity available or not.