In hospitality retrofits, LEDs get closer to incandescents: with a billion incandescent bulbs primed for replacement in the hospitality market alone, LED dimming must satisfy a demanding demographic.
Several things have combined to put energy into the spotlight, so to speak. The Energy Independence and Security Act of 2007 set a new standard for light bulbs. Under this law, most incandescent bulbs can no longer be manufactured, and are being replaced by new, screw-in light bulbs that use less energy to achieve the same level of light. The law took a phased approach, starting in January 2012, and was completely implemented by January 2014.
Additional factors, like more stringent energy codes, increases in the cost of electricity and a renewed interest in sustainable building design, have also contributed to the development of more efficient light sources, especially screw-in LED bulbs that can be used as direct replacements for incandescent bulbs. Perhaps more than any other market, the hospitality field is dependent on the familiar, comfortable quality of incandescent light and especially interested in retrofit products that meet their lighting and control expectations.
Incandescent bulbs all have the same basic qualities, and this is the level of performance any replacement bulb is expected to meet:
* They can be dimmed, smoothly and without flicker or shimmer, to very low light levels--less than 1 percent--to create different lighting aesthetics in any space.
* The bulbs are quiet--they do not buzz or hum when dimmed with a high-quality dimmer.
* The color shifts to "warm" (orange) as they are dimmed--a nuance that is universal with incandescent and halogen bulbs, but not typical of compact fluorescent or LED bulbs that do not experience color shift.
* They are generally priced under $5 each. Although LED bulbs are coming down in cost, dimmable LEDs are still significantly more expensive than comparable halogen, or even CFL bulbs. In a perfect scenario, LED bulbs would meet all these expectations while using less energy and delivering longer life (incandescent bulbs typically last about 750 hours, while LED bulbs can last up to 50,000 hours). The opportunity is tremendous--in the hospitality sector alone there are approximately 1 billion incandescent bulbs that will have to be replaced, and in many cases these bulbs will have to be dimmed to deliver flexibility and proper aesthetics.
LED options are improving rapidly, but many existing LED bulbs still have limitations that are unacceptable for the hospitality market. These include bulbs that cannot be used in totally enclosed fixtures, or in insulated or airtight recessed downlights. Moreover, many bulbs cannot be used with dimmers, or other third party devices like daylight/photo sensors, occupancy sensors or timers. Even if they are considered dimmable, the bulb may not be able to deliver the dimming range and performance required in spaces such as restaurants, lobbies and guest rooms.
Read the fine print on the packaging to understand each bulb's performance characteristics (including whether it is a dimmable bulb or not) and look to manufacturers' websites to understand what bulbs are compatible with what dimmers.
EXPECTED DIMMING PERFORMANCE
Expectations of dimming performance have been established based on years of experience with incandescent dimming. They include:
* No flicker, pop-on or dead travel. Dimming is smooth and continuous over the entire range. No dimmer can make a bulb perform beyond its dimming range or manufacturers' specifications, but choosing the right dimmer will maximize bulb performance.
* No load dependence. All incandescent/ halogen bulbs work with virtually all dimmers. Existing dimmers will typically not deliver expected performance with LED or even CFL loads, but new dimmers are available that will control all common bulb types.
* No neutral wire is required for dimming. To assure dimming performance, LED dimmers typically do require a neutral wire, which can be a challenge in retrofit situations where there may be no neutral wire in the backbox. Relatively low-cost LED technology is constantly evolving and costs for both dimmers and bulbs are coming down accordingly.
Although it is generally recognized that LEDs are inherently dimmable and controllable, it is much more difficult to get the same results dimming LEDs as those expected with incandescent bulbs. This is attributable to the electrical differences between LEDs and incandescent/halogen bulbs. And because different bulbs use different technologies, a bulb's performance with one dimmer does not predict its performance with another.
Incandescent bulbs all create light by heating tungsten wires to high temperatures in a low-pressure glass envelope, causing them to glow white-hot. Electrically speaking, these are very simple devices: the more voltage they are provided, the hotter they get, and the more light they produce. It does not matter what shape the voltage is: AC, DC, phase cut or nearly any other form will provide the same amount of light for the same RMS voltage.
LEDs behave very differently. For a given LED device, the amount of light generated is proportional to the amount of current (not voltage) passed through the device. Furthermore, the current can flow only one direction through an LED, meaning they can only tolerate DC. Finally, LEDs are inherently low-voltage devices, typically requiring a large reduction in voltage from the mains wiring.
Reducing the voltage, regulating it to DC and controlling the current are all handled by an LED driver (which is internal to the LED bulb). LED drivers are extremely varied in their design, construction and features. However, one thing they have in common is that they do not have the same electrical properties as an incandescent load. This is essentially the root cause of compatibility challenges between controls and LED bulbs or fixtures. You must work with a manufacturer who has tested multiple combinations of dimmers, bulbs and/or fixtures, and published the results, to be assured that your installation will perform as you expect.
Color quality is another common concern in retrofit applications. Incandescent bulbs "dim to warm." As they are dimmed, a color shift occurs, and they give off a familiar warm (orange) glow. Because LED bulbs do not change color as they are dimmed, the perception is that the light is cold. This is especially problematic in guest rooms and restaurants where customers are most comfortable with the familiar quality of incandescent light. Some newer LED bulbs use two different colors of white LEDs to recreate the familiar warmth of incandescent light as the bulb is dimmed.
Currently, different manufacturers may prioritize different requirements when they develop LED drivers: some may optimize for cost, some for size, some for lifetime, etc. Part of the design of the driver determines how well, and how low, it will dim and with what controls. This leads to two important conclusions:
1. The design of the driver determines the best possible dimming performance that can be achieved.
2. The compatibility of the driver with the control determines how well the driver will achieve this performance.
In essence, even the best control cannot make an LED bulb dim better (more smoothly, deeper, etc.) than it was designed to dim. Both poor driver design and improper pairing with a control can lead to unacceptable aesthetic performance, including flicker, drop-out, dead travel or acoustic noise (buzzing). Poor driver design or control pairing can also lead to reduced lifetime of the control or load. A good driver should guarantee smooth, continuous dimming to very low light levels on a wide variety of controls with no negative impact on lifetime--these parameters match the dimming performance that people have come to expect from incandescent bulbs.
NEMA is working with control, bulb and LED chip manufacturers to develop a new solid-state lighting standard: NEMA SSL 7A-2013. This is a forward-looking interface standard for forward-phase dimming of LED loads (both screw-in bulbs and fixtures), suitable for global use. The standard includes specifications to ensure reliability and basic performance of dimmers and LED loads, and provides basic requirements for bulbs and controls in regard to performance characteristics. The aim of the SSL 7A-2013 standard is to reduce the chance of experiencing LED compatibility-related problems with an installation, and make product selection easier.
In many ways, LED dimming is a brave new world. The technology is changing rapidly, and the opportunity for excellent light quality, energy savings and flexibility continues to improve, but it can be very intimidating. For retrofits in the hospitality market consider these important design guidelines:
* Use manufacturer test reports to understand bulb performance in advance.
* Use mock-ups and demos early in the design process to effectively evaluate the proposed bulb/dimmer combination.
* Ask for information above and beyond current spec sheets including compatibility, dimming range and color.
* Once an approved combination is selected, do not allow substitutions--one seemingly small change can significantly affect performance.
Finally, for best results, work with lighting designers and manufacturers who are devoted to understanding the vast assortment of LED choices and can reliably select appropriate control and bulb combinations based on performance and budget requirements.
Eric Lind is the vice president-global specifications at Lutron Electronics Co, Inc. He serves on the IES Progress Committee, the IALD Lighting Industry Resource Council and is a past member of the IES Board of Directors.
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|Date:||Aug 1, 2014|
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