Chapter Corner

Controlling LEDs

Posted in: Features, March 2015

LEDs.gifLED light sources offer energy savings, long life, excellent light quality, and new fixture options— allowing them to be used in almost any application. These advantages make LEDs an excellent choice for virtually any customer, but there are challenges associated with making sure that LEDs meet end-user expectations. Incandescent and halogen lighting, while inefficient, always offered highly predictable light quality with any control. In comparison, LEDs are much more efficient, but their dimming performance can widely by manufacturer and model.

When selecting LED products, issues with dimming compatibility probably create the greatest source of frustration. Ensuring compatibility between LED lamps, fixtures, and controls can be confusing, and if not done properly, lighting performance will suffer. To avoid callbacks and ensure a happy customer, contractors have to choose the right combination of LED loads and controls.

WHY IS CONTROL IMPORTANT?

For many customers, energy savings is top-of-mind. LEDs are energy efficient by design, and a simple LED lighting retrofit can help meet building and energy codes while reducing electricity consumption. So why include dimming control with LEDs? For the same reasons you would use dimming control on any light source – to maximize energy savings, extend system life, enhance flexibility, increase productivity, and provide a comfortable environment for building occupants. Regardless of the solution, from a single switch or dimmer to a centralized lighting control system, a bit of research can help guarantee compatibility and satisfactory performance, eliminating many of the common concerns and issues that can be seen with LED installations.

Similar to fluorescent sources, dimming LEDs saves energy at a roughly 1:1 ratio (see figure 1). For example, if you dim LEDs down to 50 percent of their light output, you save nearly 50 percent of the associated energy use.

Dimming LEDs also makes them run cooler, further extending the life of both the driver and the phosphor in the LEDs. This can double or triple the useful life of this already long-life source.

CHOOSE THE BEST FIXTURE, DRIVER, AND CONTROL COMBINATION

There is a broad spectrum of LED lamp and fixture manufacturers, providing solutions of differing price, performance, and quality. Likewise, not all controls will perform equally or are equally suitable for use with LEDs.

If all the parts and pieces are not properly selected, the result can be “dimmable” LEDs that do not work as claimed, that never turn off completely, or that flicker, pop on, or drop out, leaving the end-user unsatisfied and you with a costly call back to the job.

ASK THE RIGHT QUESTIONS

Answering a few simple questions can help align a customer’s expectations with the performance of a given LED dimming system. Look to product packaging and manufacturer support options to help provide the information you need.

1. What is the application type – retrofit or new construction?

New construction enables you to use either LED bulbs or LED fixtures, allowing a wide variety of control options. Retrofit applications are often limited to LED bulbs, and the control options will be limited as well.

LED bulbs with Edison-base sockets are usually the lowest-cost option. They generally replace standard incandescent or CFL bulbs, making them especially suitable for retrofits. These lamps have integral drivers that determine whether they are dimmable and define the dimming performance.

LED fixtures can vary from cove lights to down lights and usually have an external driver mounted on their enclosure. Some fixture manufacturers offer different driver options on the same fixture to support different control technologies or applications (such as dimmable vs. non-dimmable). LED fixtures are typically only used for new construction or major retrofit. They come at a higher price, but are typically selected for their higher level of performance (better light quality, aesthetics, and beam control) and their wider variety of control options.

2. What type of control does the LED product require?

The recent proliferation of LED lighting has caused many applications to consider moving away from phase control, which was the only choice for standard incandescent loads. Additionally, various market forces make it more likely projects will incorporate controls. Therefore, it is important be educated on the various control options (0-10V, forward or reverse phase, EcoSystem, and others) to ensure the proper pairing of the controls with fixtures that support that technology.

3. How many fixtures/lamps can be connected to one dimmer?

Overloading the dimmer is a potential problem with LED installations. All dimmers are rated for a maximum load (in volts, amps, and/or watts) that must not be exceeded. Many recent dimmers have specific ratings for LEDs, making it easy to determine how many loads can be connected to them (by dividing the dimmer’s LED load rating by the wattage of each load). For dimmers without LED-specific ratings, the incandescent rating cannot easily be used to determine the number of LED loads. This is because LED loads can produce inrush or repetitive peak currents that are greater than their wattage indicates, stressing the dimmer and potentially causing premature failure. The lamp or control manufacturer’s recommendations must be consulted in these cases.

Furthermore, some dimmers may not perform well if they are required to control a very small load. With incandescent bulbs, it was easy to meet a dimmer’s 25- 40 watt minimum load requirement, but with LEDs, multiple bulbs may be needed for the dimmer to operate properly. And, since LED loads have different electrical characteristics than their incandescent predecessors, even using sufficient LEDs to meet the minimum load may not ensure proper dimmer operation. Dimmers specifically designed for LEDs, such as the C.L. dimmer family from Lutron, have much smaller minimum loads than standard dimmers, usually just one lamp.

4. What is the dimming range of the LED bulb or fixture?

Talk to the customer about their application, and check packaging or literature for the products’ dimming range. A product that dims to 20 percent measured light (45 percent perceived light) wouldn’t make sense in a media room but may be an appropriateenergy-saving solution for an office.

5. What kind of dimming performance can you expect?

Customers expect smooth, continuous dimming with no abrupt changes in light, and they also expect dimming performance that is free of flicker, pop on, and dropout. A good driver (whether in a bulb or a fixture), paired with the proper control, will provide this assurance.

Choosing the right dimming control for the driver will ensure compatibility: Providing the necessary control signal, reducing the chance of flicker, achieving the desired dimming range, and supporting the amount of connected load. However, the driver is what determines the best achievable dimming range and the best possible dimming performance (dimming smoothness, low end light level) of the lamp or fixture. Therefore, choosing the proper LED load to begin with is critical to achieving the desired outcome.

MEET CUSTOMER EXPECTATIONS

Controlling LEDs is no longer the wild west of the lighting control industry. Technologies are improving, and control options, literature, and general knowledge is expanding. LEDs can now be effectively used in virtually any type of commercial or residential application.

Using LEDs does necessitate more careful product selection, but by choosing the right manufacturer and being aware of key issues, it is possible to provide customers with an LED lighting and control system that meets energy-saving, performance, and aesthetic expectations.

Ethan Biery is an LED Engineering Leader at Lutron Electronics, an IEC National Bronze Industry Partner. While his early career was spent developing dimming systems for large-scale commercial projects, the last five years have been spent focusing on LED technology, especially in the area of testing and improving dimming compatibility. In this role, he works with colleagues from all levels in the industry, from chipset vendors to lamp and fixture manufacturers, in order to improve compatibility between dimmers and LED light sources. His expertise means he is a regular contributor to training, technical whitepapers, application notes, and industry standards regarding LED technology.