Understand compatibility, performance, and dimming issues in LED lighting (MAGAZINE)
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This article was published in the Spring 2013 issue of IIF Magazine.
View the Table of Contents and download the PDF file of the complete Spring 2013 issue, or view the E-zine version in your browser.
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LED-based solid-state lighting (SSL) offers many potential benefits such as energy savings, but the technology comes with new challenges such as compatibility with legacy controls. Moreover, lighting specifiers and designers must understand the unique properties of LEDs to realize optimal performance in installations. Let’s consider the rationale behind dimming and discuss some key questions that can lead to lighting systems that dim to project requirements and yield satisfied customers.
The growing popularity of LED light sources is rooted in energy savings, long life, and new fixture options that enable them to be used in almost any application. A 25W LED lamp can replace the light output of a 100W incandescent lamp, deliver a useful lifetime averaging 50,000 hours (compared to 10,000-20,000 hours for fluorescent lamps and 3000 hours for halogen lamps), and offer very good color rendering. LED lamps also emit very little infrared radiation, and they contain no mercury.
These advantages ensure a strong future for LEDs, but there are challenges associated with using LEDs to meet customer expectations. Compatibility between LED lamps, drivers, and controls can be confusing, and if they are specified improperly, performance will suffer. The best strategy for selecting an LED product is a holistic approach that takes into consideration a variety of factors including the application type, required dimming performance, and control preferences.
Issues with compatibility are probably the greatest source of frustration among specifiers and their customers. Mock-up installations and expensive, time-consuming testing may be necessary before customers are confident that the proposed solution is the best solution. To smooth the pathway of a project, look for lighting control manufacturers who have already done the appropriate testing and research and can provide services to ensure successful LED lamp, driver, and control installation.
Why is control so important?
LEDs are energy efficient by design. Simply using LED lamps or fixtures can help a facility meet updated building and energy codes while reducing electrical consumption and cost. So why worry about dimming your LEDs? For the same reason you control any light source -- to maximize energy savings, extend system life, enhance flexibility, increase productivity, and provide a safe, comfortable environment for building occupants.
A wide range of controls are available -- from a single switch or dimmer to a centralized lighting control system -- to provide maximum flexibility, as well as measurement and reporting tools to help you effectively analyze the energy savings being achieved with the lighting and control installation. Easy-to-install wireless controls facilitate simple retrofit, reducing installation and programming costs and improving the return on investment (ROI).
Regardless of the control system you choose, it is critical to work with a manufacturer who can guarantee compatibility and performance, eliminating many of the common concerns and issues that are seen with LED installations.
Maximizing savings, life, and performance
Dimming LEDs, similar to the process with fluorescent sources, saves energy at a roughly 1:1 ratio (Fig. 1). This means that if you dim LEDs down to 50% of their light output, you save nearly 50% of the associated energy use. While it is true that LEDs are already very efficient compared to almost any other light source, you save even more energy by dimming them.
Dimming LEDs also makes them run cooler, extending the life of the electronic components in the driver, as well as the phosphor in the LEDs. This will potentially double or triple the useful life of the LED lamp or module. Research is ongoing to better quantify the relationship of dimming LEDs and lifetime extension.
Dimming any lamp -- incandescent, halogen, CFL, or LED -- enhances ambiance, so whether you are in a restaurant, conference room, or presentation space, you can create the environment that the lighting designer intended while helping to keep employees productive and focused. In the US, labor is the most expensive component in any business. Productive employees are a company's most valuable asset and have a direct impact on the bottom line. Yet many workers suffer fatigue and reduced motivation as the day goes on. Good lighting can halt the decline, allowing employees to remain alert and engaged.
A research study conducted by the Light Right Consortium (a DOE-organized group focused on ergonomic lighting) established that employees who were able to control their lighting environment were more comfortable, more satisfied with their work, and more motivated to continue difficult tasks. The study, "Lighting quality & office worker productivity," demonstrated that workers were able to be more persistent and vigilant throughout the day when they had greater control of their lighting environment.
Matching products to the project
To achieve optimal performance, you must choose a combination of fixtures, drivers, and controls to match your specific project requirements. LEDs are making great strides, and LED products now exist for replacing virtually any fixture type including general-purpose lighting, downlights, cove lights, and outdoor lighting. The type of control you choose will depend on the results you want to achieve. For example, in a lobby or atrium, a 20% minimum dimmed light level is typically acceptable. But in a conference room, or a restaurant, very low levels of light -- dimmed down to 1% -- are often desirable. It is important to define expectations right up front.
There is a broad spectrum of LED lamp and fixture manufacturers, and not all of them are familiar with the various control types available and the corresponding product design requirements. The same is true when it comes to controls. Not all controls are equally reliable. Dimmers and dimming systems that are specifically designed for use with LED sources will typically perform better than those designed to control incandescent sources.
If all the parts and pieces are not carefully evaluated, the result can be "dimmable" products that do not work as claimed, that never turn off completely, or that flicker, pop-on, or drop-out, leaving the end-user with the perception that dimming LEDs does not always work.
Consider all the factors
Carefully consider the following six issues to effectively align customer expectations with LED dimming system performance. If you have questions, or are unsure how to proceed, look for a manufacturer who can help walk you through the selection process, such as the LED Control Center of Excellence offered by Lutron Electronics.
1. What is the application type -- retrofit or new construction?
New construction enables you to use either LED lamps or LED fixtures and offers a wide variety of control options. Retrofit applications are often limited to LED lamps, and the control options will be limited as well. Defining the application will determine how to think about the other factors in an LED-based lighting and control system.
2. What type of LED product are you using -- an LED lamp or LED fixture?
LED lamps have Edison-base sockets and are meant to replace standard incandescent or screw-in CFL bulbs. The bases of these lamps have integral drivers that determine whether they are dimmable, and if so, the dimming performance (Fig. 2). LED fixtures can vary from cove lights to downlights and usually have an external driver. Some fixture manufacturers offer different driver options (Fig. 3) on the same fixture to support different control technologies or applications (such as dimmable vs. non-dimmable). You may even be able to specify an optimal drive from another manufacturer that includes the desired feature set.
Check with the driver or fixture manufacturer to be confident that you are choosing the right product -- drivers are available that can dim LEDs from 100% to 1% light, offering smooth continuous dimming for both constant-current and constant-voltage sources. The long-life benefits of LEDs will be reduced if the driver is not designed for an equally long life.
3. What is the dimming range?
Not all LEDs are created equal. Select the fixture or lamp that offers the dimming range suitable for your application. A product that dims to 20% measured light (45% perceived light as documented in the IESNA handbook) wouldn't make sense in a media room, but may be an appropriate energy-saving solution for an office. If an LED fixture or lamp specification sheet does not state the dimming range, you should contact the manufacturer for that important piece of information.
The dimming range of a product, either a lamp or a fixture, is based solely on the driver. Choosing the right dimming control will allow you to reduce flicker and may affect your ability to achieve the desired dimming range, but the dimmability, low-end light level, and performance of the product are determined by the driver.
4. What is the dimming performance?
Lighting designers typically focus primarily on light quality and color, but various performance anomalies such as flicker, pop-on, or drop-out may occur with some LEDs. Are these acceptable for your application?
The public's experience with incandescent/halogen dimming is that it is smooth and continuous, with no abrupt change in light level as the light source is dimmed. There is an expectation that the dimming performance will be free of flicker, pop-on, and drop-out. A good driver should account for these performance factors and still provide flicker-free, smooth, and continuous dimming of the LED source.
In summary, the driver determines the achievable dimming range and the best possible performance of the lamp or fixture. The control determines whether or not the best possible performance is realized in the application.
5. How many fixtures/lamps can be connected to one dimmer?
Applying LED loads to incandescent dimmers may not only lead to poor performance, but can also reduce control life. It is important to know how an LED load may affect the reliability of the dimmer. Indeed, overloading the dimmer is a common problem with LED system operation. All dimmers are rated for a maximum load (in volts, amps, and/or watts) that must not be exceeded. It is not as simple as dividing the 600W dimmer rating by the 15W LED lamp you have selected to determine that 40 lamps can be used on a circuit.
Each 15W LED lamp may only draw 10W continuously, but may have a startup inrush current or repetitive current during every half-cycle that makes it appear much worse (Figs. 4 and 5). For example, a 15W LED lamp may appear to the dimmer as a 100W incandescent load from the perspective of inrush current, so if you use more than 90W in aggregate of that LED product, the dimmer may be stressed, shortening its lifetime.
Similarly, some LED drivers may not perform well if they are required to control a very minimal load. It is easy to meet the 25-40W minimum load requirement with incandescent bulbs, but with LEDs, four or more bulbs may be needed on a dimmer in order to meet the required minimum load. And, since LED loads have different electrical characteristics than their incandescent predecessors, even meeting the minimum wattage load may not ensure proper dimmer operation.
6. On what type of control does the LED product operate?
There are many types of controls and control systems from high voltage (traditional phase control or reverse phase control) to low voltage (0-10V, DMX, DALI) and even some new entries with embedded wireless connectivity in the lamp/fixture. Which one will work best for both your application and the LEDs?
While there have been a variety of control technologies available for years, the proliferation of LED lighting has caused many applications to move away from the typical control choices used for standard incandescent loads. Additionally, the inherent controllability of LEDs makes it likely more applications will incorporate controls. Therefore, becoming educated on the types of control technologies available, such as 0-10V, forward or reverse phase, EcoSystem, or others, will be necessary to ensure the proper pairing of the controls with fixtures that support that technology.
A holistic approach to LED control can help meet and exceed customer expectations. The LEDs control arena is no longer the Wild West of the lighting control industry. Technologies are improving, control options are expanding, literature and general knowledge is increasing, and LEDs can now be effectively used in virtually any type of commercial application. By choosing the right manufacturer and considering key issues, it will be easier than ever to provide customers with an LED lighting and control system that meets energy-saving, performance, and aesthetic expectations.
