LED Lighting: TCO Part II – The Cost of the Lighting System

Breaking Down the Costs of Owning and LED Lighting System

TCO Graphic Part II

The Total Cost of Ownership is buried within the lighting system design, individual components, and manufacturing process. Some can be easily identified, while others are virtually impossible to discern without the manufacturer’s help.

PURCHASE PRICE: The LED Lighting Kit. A ‘kit’ is the complete set of individual components that make up the light system:

  1. The Fixture
  2. The Light Engine
  3. The LED Component
  4. Power Supply
  5. Power Cables

The Fixture can range from a simple extruded aluminum bar to a complex housing containing the heat sink, cooling fans, the electrical interface, power circuitry, power controls and control interfaces, sensors, and both light optics and protective lenses. In most instances (but not all), the fixture also holds the Light Engine. The entire fixture is priced (appropriately) as one unit. Fixtures have related installation and maintenance costs. Fans (active cooling) are more expensive to operate and maintain than a fixture that uses heat sinks only.

The Light Engine holds the LED components (or chips) that emit light. Light Engines are analogous to a bulb, but are typically integrated into the fixture (can’t be removed or replaced). High quality Light Engines are made of a metal-core printed circuit board (PCB) that holds the LED chips and makes the electrical connection between the incoming electrical current and the LED chips. The PCB boards are bonded to the heat sink to conduct heat away and maintain the operating temperature of the LED chips. Alternatively, individual LED chips with a metal substrate (often called a chip-on-board of COB) can attached individually to the heat sink with electrical connections made between each COB. The method of the connections vary widely in quality. Poor quality connections result in more frequent maintenance costs. Because Light Engines are integrated into the fixture, when they fail (and they do fail), the entire fixture must be replaced. The product warranty will pay for the replacement, but not the labor to monitor the lights, identify failures, remove the fixture, and replace it. An undetected Light Engine failure reduces crop production, as does the delay between replacements. Individual LED chip failures occur (much more often than the salesperson will tell you) and exasperate the problem. The higher the quality of the Light Engine, the fewer failures and the lower the maintenance costs. In most cases, the added cost of buying quality is worth it. We know of just one manufacturer who uses a replaceable Light Engine, which provides a number of advantages over an integrated Light Engine – the most obvious of which is avoiding replacing the entire fixture when a Light Engine fails. For all other systems, the Light Engine and Fixture are bound to each other, with the failure of any of the components causing the failure of the total system.

The LED Component (chip) deserves a separate discussion thread. They are the most important part of the entire lighting system, and vary widely in terms of performance and quality. There are only a dozen or so manufacturers of suitable LED chips (globally), and among these, there are only a handful that stand out in terms of performance and quality. Evaluating the quality of the epitaxy, bin, phosphor, and optics of the LED chips is beyond the scope of this article, however, there are two heuristic measures that summarize the differences; efficacy (performance) and L80 ratings (quality). Efficacy is the measure of light output to energy input, and has (by far) the largest economic impact on costs related to the lighting system. Further complicating the analysis is that efficacy is different for each spectra (color) of LED chip, requiring an efficacy calculation for the entire fixture. And the variance of fixture-level efficacy can be large – from less than 1.0 PPF/watt to 1.8 PPF/watt – a stunning difference, considering that the latter requires 80% less energy to produce the same amount of light. Our LED P/Q Rankings focus on fixture efficacy as the primary attribute of performance. The higher the efficacy, the lower your cost/lb of food will be. (note: we will discuss LED chip quality in a future article).

The Power Supply is typically separate from the Fixture and is almost always manufactured by a third party and priced separately. The Power Supply converts AC current to DC current (in most instances), and contains the circuitry for current control and dimming. These processes result in electrical losses of 8% to 15%, which you pay for in the form of electricity you have purchased (at the wall plug) but which is lost before it can power the Light Engine. The efficiency differences between Power Supplies is second only to LED chip efficacy as a cost consideration. The difference between a 15% loss and an 8% loss in significant in terms of your electrical costs. The efficacy measure of the LED P/Q Rankings encompasses a measure of the Power Supply efficiency, meaning it’s the best way to evaluate the energy costs of the entire system.

The Power Cable varies only slightly from one product to another, with the primary consideration being the distance (length) of the Power Cable between the Power Supply and the Fixture. All cables have ‘line’ losses that increase as the distance increases. When Power Supplies are located in close proximity to the fixture, these losses are trivial, but if Power Supplies are located away from the grow room, they can become meaningful.

Installation Costs. The cost of installing the fixture is almost always underestimated – and it can vary considerably from one product to another. Installing several light bars is more costly than installing a light panel that covers a greater area. More costly still is the cost of electrical wiring. AC connections require an electrician, so minimizing them reduces the installation costs. In general, you should plan for installation to add between 15% and 20% (in labor costs) to the initial purchase price of the light system (note: we will address thermal management, controls, sensors, optics and lenses needed for IP ratings in a separate article).

We noted earlier that identifying all of these costs without the help of the manufacturer is impossible. This is the main reason we work with manufacturers to aggregate the data and provide it in the form of the LED P/Q Rankings. We can’t emphasize enough how valuable we believe the Rankings are to you in your equipment evaluation.



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