A Practical Approach to Engineering the System (Low-Voltage Lighting)
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A Practical Approach to Engineering the System (Low-Voltage Lighting)

Sep 21, 2018
Video Length:  52:24
Presented By:  Brian Qualls
Many designers will only create a fixture placement plan when it comes to landscape lighting. Aimed at landscape architects and other designers, this webinar will show the engineering side of a low-voltage system. We'll move past the idea that "we are not electrical engineers" and show you how low-voltage lighting has the same design fundamentals as irrigation systems. Once you've viewed this presentation, you'll have a better understanding of how low-voltage lighting works and will no longer need to rely on “others” for a complete lighting system design.

Webinar Contents:

Note: The following catalog of content covered in this webinar is time stamped to allow you to follow along or skip to sections of the video that are relevant to your questions. You can also search for content on this page using the FIND command in your browser (CTRL + F in Windows, Command + F in Mac OS.)


  • Intro/TOC
  • Definitions
    • Lighting Equipment in Comparison with Irrigation Equipment
    • Watt vs. Amp vs. Volt
    • Irrigation Rates vs. Low-Voltage Lighting Rates
  • Ohm’s Law
  • Voltage Drop
  • Wiring Methods
  • Connections
  • LEDs

0:00 – 4:05 : Intro/TOC

Brian’s contact info:

Brian Qualls, RLA

Business Development Manager, Unique Lighting


Phone: 480-381-6901


What is low-voltage landscape lighting? (2:45)

  • Easiest method of providing lighting to the outdoor property for the purpose of enhancement, atmosphere, safety, and security.
  • The systems are based on 12 vs. 120 volts.
  • It’s one of the fastest-growing segments in the green industry.


Why do we light? (3:18)

  • It visually enhances your designs well into the night.
  • If you don’t light it, you can’t see it.
  • Lighting alters the way outdoor space is used.
  • Lighting changes the feel of space.
  • Lighting can visually connect spaces together.
  • There is no sense of space without light.
  • Why would you let someone else decide what to light?


Other reasons to light (3:40):

  • Promote safety and security
  • Create emotion
  • Create direction
  • Get noticed
  • Our clients want to enjoy their landscapes well into the night.

4:06 – 8:10: Definitions

National Electric Code (NEC) Article 411-2 (4:06):

Lighting systems operating at 30 volts or less: A lighting system consisting of an isolation power supply operation at 30 volts or less, under any load condition, with one or more secondary circuits, each limited to 25 amperes maximum, supplying lighting fixtures and associated equipment identified for the use.


Lighting Equipment in Comparison with Irrigation Equipment (4:49)





Spray heads






Point of connection (POC)






















Primary power






Watt vs. Amp vs. Volt (5:45)

Watt (6:10)

A unit of electrical power. Lamps are rated in watts to indicate the rate at which they consume energy. We recognize this on how bright a lamp is perceived at its proper voltage.


Amp (6:20)

A measure of electrical current. In lighting, the current is related to voltage and power as follows: watts (power) = volts x amps (current)


Volt (6:27)

A measure of “electrical pressure” between two points. The higher the voltage, the more current will be pushed through the wire. The volt specification of the lamp is the electrical “pressure” required to illuminate the lamp at its ideal brightness.


Irrigation Rates vs. Low-Voltage Lighting Rates (6:30)





Gallons per minute (GPM)




Velocity (FPS)








Low-voltage lighting







8:11 – 10:51: Ohm’s Law

Ohm’s law: Watts / Volts = Amps


Helps with:

  • Pre-planning
  • Figuring the max allowable amps on a transformer
  • Double-checking your work


Examples of Ohm’s Law applied (8:55)

  • 240 watts / 12 volts       =      20 amps
  • 240 watts / 24 volts       =      10 amps
  • 240 watts / 120 volts     =        2 amps
  • 240 watts / 240 volts     =        1 amps


(As voltage goes up, amps go down.)


In regards to low voltage, the amp is the most important aspect of Ohm’s Law. Everything we touch, design, and install has a max amp rating.

10:52 – 34:27: Voltage Drop

What is voltage drop? (10:52)

Voltage drop is the rapid decrease in voltage as a result of several factors on a system, including resistance of wire, lamp load, wire sizing, incoming voltage, and much more.


Why do we care about voltage drop? (12:30)

  • Dim lights
  • Lamp life shortened
  • “Ugly” lighting portrait


Visual example of voltage drop (12:40)


How to overcome voltage drop? (13:35)

  • Correct sizing of transformer
  • Correct wiring design & wire size


Voltage drop examples (14:38)

12-volt halogen

Minimum: 10.8 volts

Maximum: 12.0 volts


= 1.2-volt window


12-volt LED

 Minimum: 10.0 volts

Maximum: 15.0 volts


= 5-volt window


How do designers compensate for voltage drop? (17:20)

  • Use larger wire (less resistance)
  • Limit the circuit length / locate transformers closer to the lights
  • Let the electrical engineer worry about it
  • Use a multi-tap transformer
  • Lower the lamp load (LED)
  • Some don’t realize there is a problem – let the contractor figure it out.


Voltage drop rule of thumb (19:00)

What is the voltage drop of a 12-volt, 40-watt lamp, 100 feet away from the transformer on 12/2 cable?


Brian’s Unique Lighting Systems Transformer and Wire Sizing Formula (“Wiring Wizard”) (19:45)

(available for download from the Unique Lighting website) 


More about amps (21:45):

  • 10 ga wire = 30 amps or 300 watts
  • 12 ga wire = 20 amps or 240 watts
  • 14 ga wire = 15 amps or 180 watts
  • 16 ga wire = 10 amps or 120 watts


Most transformers are built with a 25-amp breaker.


Where does voltage drop occur? (26:05)

  • Power source (120 – 240 volt)
  • Transformer
  • Wire length
  • Wire size
  • Lamp load
  • All connections
  • Tarnished wire


Primary power (28:48)

  • The primary (120-volt) power is not always perfect.
  • The more load you put onto circuit, the more voltage drop you will have.
  • The primary voltage can change throughout the day.


Transformers (29:33)

12-volt transformer:


10:1 ratio

Or divide the primary power by 10.


Example: 120v / 10 = 12


We solve voltage drop at the transformer. (30:58)

34:28 – 41:50: Wiring Methods

Much like irrigation design, lighting design includes several types of “mainline” wiring methods.


Daisy chain wiring design (the most common method) (34:38)

Daisy chain wiring can cause considerable voltage drop along the wire.


Poor connections will ruin any system.


“T” method wiring (37:05)

“T” method wiring can help with voltage drop, but it adds more potential failure points.


Loop wiring design (37:25)

The loop method adds more wire and can often create a dead short at the end of the loop.


Hub method (37:40)

This method reduces the number of connections to two and puts them inside a protective valve box with a fuse that can replace the transformer as the safety catch for the entire system.


Expanded hub method (38:35)

This method incorporates a master hub and satellite hubs, resulting in only one run back to the transformer, reducing failure points. It’s also easier to install.


Comparison of methods (40:23):



Wiring method


Daisy chain




Loop method


Hub method

# of connections









# of connections in the ground









Equal voltage to lamps?












Troubleshooting a hub system (40:35)


Advantages of a hub system (41:10):

  • Quality control of wiring infrastructure for an outdoor lighting system
  • No connections buried in the ground
  • Connections are protected in a box and can be used with in-line fuse protection.
  • Easy to troubleshoot and/or maintain (i.e., check voltage, amperage, etc.)
  • Maintains quality long-term connection
  • Equal voltage distribution to every fixture


Hub installation detail (41:23)

41:51 – 44:15: Connections

  • A loose connection creates heat and can melt the connection device and/or the cable.
  • A loose connection creates voltage drop.
  • If your connection is not sealed, it will allow moisture to wick through your wire.


Examples of bad connection and placement (42:00)


Wire nuts are made for solid copper wire – they are threaded and thus create threads on the solid wire that prevent the nut from being pulled off. Low-voltage systems are wired with stranded wire (i.e., a wire consisting of several individual wires), so they don’t provide anything for a wire nut to grab onto.


Examples of good connections (44:30)

  • Allen head screws
  • Flat-head screws
  • Buchanan crimps (copper crimps)

45:16 – end: LEDs

About correlated color temperature (CCT) – measured in Kelvin (K) (45:16)

  • 10,000K: A very high CCT used in horticulture and aquarium applications
  • 6,000 – 6,500K: A high-CCT daylight source used to simulate average outdoor lighting conditions
  • 5,000K: Enhances blues, dulls reds, and imparts a bluish tint to whites and greens. Used mainly in museums, jewelry stores, and hospitals.
  • 3,700 – 4,000K: Neutral-colored light. Enhances colors equally without emphasizing yellow or blue. Used mainly in showrooms, bookstores, and office areas.
  • 3,000 – 3,200K: Most commonly used in homes but also in libraries, office areas, and retail stores.
  • 2,700K: Used in restaurants, hotel lobbies, boutiques, and homes.


Unique Lighting sells more 2,700K lighting than any other color, but Brian tries to encourage the 3,000 – 3,200K range, which provide more emphasis on the landscaping and more color accuracy.



Photo example of a setting that incorporates 100% low-voltage lighting (48:15)


Question: What is your recommendation for the best wire connection method? (50:14)

Answer: Brian recommends using the hub method with a barrel connector (flat-head screw). The barrel connector allows him to add wires if necessary without having to cut the existing wires.

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