The science of landscape lighting

12 Oct The science of landscape lighting

When designed and installed properly, a landscapelighting system enables clients to enjoy their watershapes and landscapes well after the sun goes down.But achieving those satisfactory results, says lighting expert Mike Gambino, requires an understandingnot only of the aesthetics of lighting design, but alsoan appreciation of the technology behind the beautyand an ability to lay components out in ways thatelectrically balance the system. By Mike Gambinosired “halogen effect” therefore cannotoccur and the light output will be significantly dimmed. Conversely,if the voltage is too high, the lamps will burn toobrightly and the desired visual effects willbe distorted by hot spots. Moreover,when lights don’t operate at the propervoltages – high or low – they don’t last aslong as they should. These early burnoutsfrustrate clients,which is one of the mainreasons I receive calls to work on existing systems.The picture is somewhat complicatedby the fact that halogen lamps are available for operation over a range of voltages,with 12 and 120-volt units being themost common. To me, the lowest-voltage (12-volt) option is the best (and safest)option: When installed in properly designed systems,these lamps offer tremendous output relative to energy consumption and will last a long,long time.The specification sheets for most ofthese 12-volt halogen lamps say that 10.8volts are needed to generate enough heatto create and perpetuate the halogen effect. When input falls below that level,these lights can’t work as designed – it’sas simple as that.But as I see it,one of the keys to working successfully with halogen lamps is tostop thinking about them as individualcomponents and instead to see them aslinks in systems of variable lengths,withelectrical balance within any given system being the goal.Working Toward a BalanceIt’s not a perfect analogy, but youmight find it useful as watershapers tothink of lighting systems as being similar in some ways to hydraulic systems:Where every jet in a spa has a recommended operating tolerance relative toflow and pressure and a balanced hydraulic system is one that creates a condition where all jets in the system operate within the proper range, the samegenerally holds true for lighting systems:You want to create a system where everyfixture operates within its specified range.Those who don’t understand the needfor this balance often (and unwittingly)design systems where one lamp mightbe receiving 9 volts and another receiving 13 or more. You don’t have to be anelectrical engineer to get the point that,under those conditions,some lights willbe dim while others will burn too hotand prematurely fail. To avoid theseproblems, I make certain that every fixture in a cluster of lights operates within a half volt of the others within the 11-to-12-volt range.This objective puts a tremendousamount of pressure on the system-designprocess and the way I lay out my systems.In my view, the best place to start iswith the power feed (or “home run”),which is the wire that delivers powerfrom the transformer to the fixtures. Justas with water and pressure in hydraulicsystems,as electricity flows over a lengthof wire, voltage drops or attenuates because of resistance it meets along the way.Therefore, I lay out my systems so thatthese home runs feed small clusters oflights situated no more than several feetapart from each other.My systems are all arranged so that thehome run connects to a fixture that actsas a hub,with all other fixtures on that circuit wired to either side of the hub inwhat’s referred to as the “T method.” Acommon (and incorrect) alternative to thisis the series (“daisy chain”) approach inwhich the home run feeds a single fixture;wires then pass in sequence to a succession of other fixtures along the line. Usingthis option, fixtures at the end of the linewill inevitably receive less voltage than theone wired directly to the home run.I group my systems in sets of three tofive fixtures with lines branching off ofthe hub because this arrangement helpsme equalize the voltage at each fixture.I also take a conservative approach to thestandard manufacturer recommendation that there should be no more than25 feet of wire between the home runand the last fixture on a given side of thehub. In fact, I seldom come anywhereclose to pressing that limit: If a layouthas me putting a fixture any more than15 feet away from the home run, I’ll usea separate home run for that fixture.Yes, this often means my systems become quite complicated in a schematicsense, but it’s the only way I’ve found todeliver the desired,fully balanced resultsmy clients crave.Wired UpAfter appropriate layout, the next keyto good system design has to do with thewires chosen to get the job done.There are several schools of thoughton this,but experience has taught me tostick with 12-gauge wire – and this is despite the fact that many manufacturers48 WATERsHAPES  FEBRUARY 2008In the field, I start the layout process by placing flags where I want lighting fixtures to go, thenwork my way back through each branching series and home run in the system to ensure eachgroup of fixtures will be adequately served with respect to power delivery.pre-install 16-gauge wires with their fixtures as 25-foot leads ready for connection to the home run. As I see it,16-gaugewire leads to a high level of voltage dropthat I can avoid by using 12-gauge wirewith runs of a more conservative length.Without delving deep into electricaltheory, lamp wattage is another factorhere. Most low-voltage lamps operate atbetween 20 and 50 watts, with higherwattage meaning brighter light andgreater resistance (and voltage drop) atthat fixture. Using this consideration tomy advantage,I always connect my homerun to the fixture operating at the highest wattage.If, for example, I have a cluster withfour fixtures, two operating at 35 wattsand two at 20 watts,I’ll establish the hubat one of the 35-watt fixtures. Then I’llrun one wire to the other 35-watt fixtureand the other to one of the 20-watt fixtures and then the next 20-watt fixture,thus balancing the voltage drop to theWATERsHAPES  FEBRUARY 2008 49I’m a firm believer in checking and rechecking voltage outputs and amperage draws at the transformer.  As I see it, a multimeter is to a low voltage landscape lighter what a stethoscope is toa doctor:  It’s the only way I’ve found to be assured that lamps in the system are getting powerat the proper level. (Notice that all cables are color-coded for easy identification in the field.)I typically install the home run of cable directly to the ‘middle’ fixture in any given grouping and test the voltage there to determine the power terminal on the transformer to which I will be connecting that particular wire to achieve an optimal level of 11.4 to 11.8 volts.  As long as the otherfixtures in the grouping are relatively close to this power connection, there’s no need to take readings at the other fixtures.  greatest degree possible for that set offixtures,with 35 watts on one side of thehub and 40 on the other.Again, distance is extremely important: If,using the example just described,the 35-watt fixtures are just five feet apartand the hub fixture is operating at 11.5volts,you’ll probably only lose about twotenths of a volt between those fixtures –well within the target operating range.When the distance is greater and I see avoltage drop of, say, half a volt or more,I’ll sidestep any potential problems by establishing a separate home run.As far as installation is concerned, Idepart from some other lighting expertsin that I don’t typically use junction boxes to create hubs. Instead, I’ll wire thehome run directly to the fixture itself.I do so because, through the years, I’vefound that the added crimp connectionswhere the 25 feet of 16-gauge wire transitions to the 18-gauge socket wire sometimes come apart; moreover, junctionboxes themselves can be hard to find later on,especially if the landscape has subsequently been altered in some way.Transformed RealityThe next key to creating an effective,satisfying lighting system has to do withknowing the capabilities and limitationsof the transformers you’re using.These days, most commercially available low-voltage lighting systems usemulti-tap transformers. These units havemultiple ports or taps that connect at different voltage levels,commonly as 11- to15-volt outputs in single-volt increments.Connecting home runs to the differenttaps enables you to compensate for voltage losses experienced with a given line.The problem with transformers,however, is that they’re not all created equal.Let’s say, for illustration, that you havetwo identical systems wired to transformers that have the same nominal outputs but come from different manufacturers. Experience tells me that onemight deliver the exact specified voltage,but the other could be off by a volt oreven more. That’s a huge difference withthe sort of sensitive systems we’re dealing with: If you’re not aware of the idiosyncrasies of the transformer, you cando everything right and still end up withan out-of-balance system because youdon’t know the actual voltage you’re delivering to the hub.The reason for this supplier-to-supplier variability is the fact that there areno standards for how transformersshould react once loads are placed onthem. Each vendor chooses which sizeof wire to use in their cores and coils,forexample,and each one chooses a systemconfiguration. In addition,when transformers are checked on the assemblyline, they are tested unloaded for proper output despite the fact that a load willchange output to differing degrees.Some might argue the point with me,but this variability in performance hasled me to ignore the charts that accompany transformers. Instead,the only wayto get predictable results is to mock systems up and check outputs with a voltmeter: Only then can you be absolutely sure of the voltage level you’re delivering to the hub.In my own practice,I’ve become so obsessed with controlling transformer outputs that I now work with a vendor thatmakes me units featuring taps at half-voltincrements – that is,11.5,12,12.5,13 and13.5 volts on up to 15 volts. This enablesme to create extremely precise voltagelevels for various lighting clusters whilestaying within the 11-to-12-volt operating range with each of my fixtures.This can be done with single-volt-interval transformers, but I’ve found this50 WATERsHAPES  FEBRUARY 2008This transformer unit is typical of those I use in my projects.  It’s a custom style I’ve worked outwith one of my suppliers and has the advantage of allowing me to adjust voltages at 0.5 voltincrements – a big edge when it comes to setting up groups of lamps so they all receive powerwithin the target range.  In addition, this unit features magnetic primary- and secondary-circuitprotection, bypass of control modules for service, a manual override, LED indicator lights andenough room to hold three control devices, such as a timer, a photocell and a dimmer switch.52 WATERsHAPES  FEBRUARY 2008fine-tuning enhancement to be most helpful, especially whenyou have 11.2 volts at the hub: This will result in less than 11volts being delivered to downstream fixtures, but moving upto the next-higher tap will leave you with an unacceptable 12.2volts at the hub. With 0.5-volt increments, however, 11.7 voltsis just right.The other big variable with transformers is simply how manycables you can connect to them. The units I use have supersized terminals to which I can attach up to eight 12-gauge cables per common tap (of which I have two per 25-amp circuit),thus giving me the capability of connecting 16 cables. Someunits have smaller terminals that handle just three cables – acapacity factor that plays a large role in system design.Also,there are big differences in quality with respect to the connections themselves: Some transformers, for example, enableto you to make internal connections, while others (generally onthe low end) have only external terminals that will be exposedto the elements and other potential types of damage.At the SourceMoving even farther back along the electrical chain of things,it’s important to ensure that the transformers in any given system aren’t overloading the breakers on a home’s electrical service panel. A 120-volt circuit will support a total of 2,400 watts,but it is best never to load them with more than 80 percent ofthat capacity,meaning you can predictably draw approximately1,800 watts from any single 120-amp circuit.On small projects,for example,if you have a dedicated breaker for the lighting system, a single circuit often does the trick asit takes many 20- to 50-watt fixtures to exceed the 1,800-watt level. Obviously,however,if you have a large system with hundredsof fixtures,you need to be aware of circuitcapacity and make provision to tap intomultiple breakers.Some lighting specialists get themselvesinto trouble when their systems share acircuit with other systems – pool equipment, for example. The other systemmight demand a lion’s share of the circuit’s available wattage – so much so thatwhen everything is operating, the loadwill exceed capacity and the circuit breaker will overheat and cut off all power.The best situation is one in whichthe lighting has its own circuit. Failingthat, you need to know the peak drawof all other devices on the line andplan accordingly.In addition, you need to consideravailable amperage. As a rule, I prefertapping into 120-volt circuits that operate at 20 rather than 15 amps. Thereason for this is straightforward: A15-amp circuit is wired with 14-gaugeThe length of a wire run in a lighting system makes a big differencein performance because of voltage drop.  In this case, for example,the need to bury the cable along meandering contours added to thelength of the wire needed to create the home run – not necessarilya huge factor, but enough of one that it required me to recheck voltages once everything was in place.How Low is ‘Low’?What do we mean when we say “low voltage”?These days, there are two schools of thought:  To some, low voltage means anything lower than 30 volts (as in the National Electric Code) despite the fact that theUnderwriters Laboratories (UL) won’t approve transformers operating at levels greaterthan 15 volts.  Indeed, some manufacturers still produce systems that operate at higher voltages, but I’m in the other camp, which means that I believe  low voltage refersto those systems that operate at UL-approved levels of 15 volts or lower.  The biggest problem I see with systems that operate above 15 volts is that, whena light or two burns out, the voltage levels at the other fixtures rise dramatically andwill burn out  remaining lamps in rapid order.  (This happens because a burnt-outlamp offers no resistance in the line, so voltage levels rise for other lamps on the circuit.)  When more lamps burn out, the problems multiply and you have a dominoeffect that will harm every lamp on a particular line.  (This is a particular problem oncircuits connected to taps of higher than 15 volts.  Another issue, of course, is inspections:  Although such checks are rare, landscapelighting systems are sometimes scrutinized and you can run into problems for using equipment that lacks UL approval.– M.G.54 WATERsHAPES  FEBRUARY 2008wire and creates a greater voltage dropon the 120-volt or primary side thandoes the 12-gauge wire used with 20-amp circuits. That’s important andcues us into the fact that we need toconsider the voltage drop on the 120-volt side of the system – that is, lossesthat happen before the power everreaches the transformer.In systems where you can locate thetransformers relatively close to the service panel (as is often the case with newconstruction), this sort of voltage dropisn’t likely to be much of an issue. Butwhere you’re adding lights to an existingproperty, the transformers might be setat some distance from the service panel, making it imperative for you to factor in the voltage drop and design yoursystem accordingly.Again,these electrical-system conceptsare roughly analogous to hydraulic systems and the flow, pressure and resistance found in water lines: You can onlydivide the flow up based on what’s available. Thus, a 12-guage wire connectedto a 20-amp, 120-volt circuit only a fewfeet or inches away from the source delivers more capacity than does one wherethe electricity is flowing over a longerrun before it reaches the transformer.Practical TermsWhen you break all of this down andlook at the lighting process as a methodical set of key steps, it all begins tomake sense. Just as with hydraulics, it’sa case of science and art going hand inhand: If you want to achieve the desired results, you need to know what’sinvolved in both. In my case – and ina basic approach I suspect is used bywatershapers as well – I start by designing projects in aesthetic terms, thendouble back and lay out the electricalsystem to accommodate the results I’mtrying to achieve.Once the artistic game plan is in place,I flag the entire system,locating each fixture so I can see the length of the wireruns and determine the loads within thesystem. Then I break the system up intoclusters based on the layout.To illustrate,let’s consider a large property that requires 120 fixtures and 10 multi-tap transformers. That’s intimidatingon its face,but if you break it all down andlook at it as a series of vignettes, it’s relatively easy to balance the loads on eachhome run. In other words, a big systemis really just a combination of smaller,more manageable parts.Before I get that far, however, I ascertain the balance on the 120-volt side (thatis,from the circuit breaker on the servicepanel to the transformer) and on thelow-voltage side (from the transformerto the hub and the fixtures on that line).The more transformers you add to a120-volt line or the more fixtures to asingle hub, the greater the voltage drop.Thus, what you’re really doing is considering the voltage for each groupingof lights all the way from the service panel and through the transformer to thefixtures themselves.This may all seem terribly complicated,but experience helps – and there’s nosubstitute for starting off with the rightway of looking at these systems on a scientific basis. But where I get the impression that working with all but themost complicated hydraulic systems canbe a matter of some approximation onthe part of a watershaper, my work as adesigner of electrical systems calls for aprecision that can’t be left to habit, supposition or chance.This is why,when I hook up a system,I’ll bury all the connections to the fixtures except for the fixture linked to thehome run: This is where I do finalchecks on voltage levels.Generally,I start by connecting everything to the 12-volt outputs on the transformers, having color-coded every wireso I can keep track of which clusters I’mtesting. If I test the blue wire, for example,and it reads 10 volts at the home runfixture, I know that I need to move thatone from the 12-volt to the 14-volt tap tobump it up by two volts. If the yellow wiretests at 10.5 volts at the hub, I’ll move itfrom the 12-volt to the 13-volt terminalto move it into the desired range.Careful ConsiderationsMake no mistake: This testing processis absolutely critical. If I test a systemand can’t bring the voltages within thedesired range by adjusting the connections at the transformer, then I need toreconfigure layouts so that each homerun operates within the target range.This is why the half-volt incrementson my custom transformers come inhandy: With this flexibility,I can almostalways hit my targets without having togo back to the drawing board.While I suspect some of you out therewill want to take this information and apply it yourselves, as I mentioned at theoutset,that’s not my goal here. Ultimately,what I’m hoping to foster is your increased awareness of the issues involvedWATERsHAPES  FEBRUARY 2008 55in good lighting design and give you aworking vocabulary that will let you speakwith lighting contractors on an informedbasis and be better advocates for yourclients.Indeed, creating perfectly balancedsystems takes experience and a polished,educated,experienced understanding ofhow all the electrical factors involvedin lighting-system design work together. As with many endeavors, there’s abroad range of quality with respect toavailable products and the expertise ofthe designer or installer, so being informed is your best assurance of obtaining good results.As I think you can tell, my own approach involves leaving little (if anything)to chance and doing all I can to apply myknowledge and experience to delivergreatresults. Ultimately,you need someof this sort of understanding to serve thebest interests of your clients and makecertain they’re happy when the switches are thrown and the lights bring yournighttime settings to life.There’s a simple reason why I want my lighting systems to perform to the best of theirtechnological capability for as long an operating life as possible:  When things get thiscomplex, maintenance becomes a huge issue.  No client will be satisfied if there’s a regular need to have someone scamper over therocks to keep things looking their bes