LEDs Under Control

It wasn’t long ago that light-emitting diodes (LEDs) were used primarily in very specific applications, such as indicator lights and exit signs. The deployment of white LEDs for general illumination applications always seemed in sight but out of reach. Now, LEDs are being designed into applications as diverse as aviation lighting, automotive headlamps, advertising, general lighting, traffic signals and camera flashes. Primarily of import to this market, LEDs are even replacing incandescent and fluorescent lighting.

LEDs are solid-state chips that convert electrical current into visible light. The light they emit is directly proportional to the amount of current that drives them, according to Naveen Tumula, product group marketing manager for Osram Sylvania, Danvers, Mass.

“The technology is proprietary for every manufacturer, but overall, they follow the same phosphor-conversion concept, similar to fluorescent lamps,” he said. 

In general illumination applications, the blue light generated by the electrical current is absorbed when it contacts the LED’s phosphor, and, in turn, the phosphor emits white light.

“The properties of that light, such as color temperature, color rendering index, or color consistency can all be tuned and adjusted by the LED manufacturer as desired,” Tumula said. 

For signage, TVs and theatrical applications, red/green/blue LEDs are each combined in varying intensities to create any visible color. Outputs range from 10–200 lumens per watt.

LEDs benefits include higher efficiency and efficacy (lumens per watt), longevity, lower heat load, improved flexibility, and more options for light output and color control, according to Bill Grande, senior director of product management for Leviton Manufacturing Co. Inc., Melville, N.Y.

“One of the main differences, beyond efficiency, between LEDs and incandescent lights is that LEDs offer a more concise beam of lighting, enabling designers to create lamps in various configurations and arrays,” he said.

According to a May 2014 technical white paper from Lutron Electronics Co. Inc., Coopersburg, Pa., there are two distinct types of LED lighting: 1) the LED lamp, which typically has a screw-in, Edison-based socket meant to replace standard incandescent or screw-in compact fluorescent lamps, and 2) the LED fixture, which varies from cove and downlights to pendant luminaires and troffer fixtures. Fixture manufacturers usually offer different driver options for the same fixture to support various control technologies or applications.

“The LED driver converts the incoming line-voltage power to the regulated power required by the LED lamp,” said Rick Angel, Lutron senior vice president. 

Because LEDs react quickly to the power reaching them, a high quality and stable driver determines the LED’s light output and produces flicker-free, consistent light.

Dimming and controlling

The reasons to dim and control LEDs are the same as for any light source. Dimming provides further energy savings for the lamp, allows the LEDs to run cooler and extend their lifespan even longer, and reduces heating, ventilating and air conditioning building loads.

“Dimming LEDs provides the end-user with reduced energy consumption, reduced lifetime costs of the LEDs, and offers the ability to create multiple lighting scenes,” Angel said.

In terms of energy savings, there is a proportional reduction of energy consumption with dimming an LED; that is, if an LED is dimmed by 50 percent, there is a 50 percent savings in energy consumption.

“In addition, LEDs maintain their efficiency when dimmed, while the lumens per watt of incandescents are reduced when those lamps are dimmed,” said Ethan Biery, LED engineering leader at Lutron.

When dimmed, LEDs run cooler, which extends the life of both the driver’s electronic components and the yellow phosphor. Cooler operation also increases the LED’s lumen maintenance (the slow decrease in light output over a light source’s lifetime). According to the Lutron white paper, research is ongoing in better quantifying the relationship of dimming LEDs and lifetime extension.

Dimming an LED also enables the end-user, whether it’s a restaurant, theater, residence, hotel lobby or office space, to create the environment the designer intended and enhance the ambiance and atmosphere.

“Dimming LEDs enables users to set the desired light levels for the time of day or for events that are happening in the space,” said Al Lombardi, Leviton’s senior director of engineering. 

Dimming controls can also increase productivity by allowing the user to select the right level needed for various tasks and by reducing eyestrain and fatigue.

According to the Lutron white paper, it is important to understand that the dimming range of any LED product is based solely on the driver. The integral driver of a screw-in LED retrofit lamp or the external driver of an LED fixture will determine how low the connected LED module is capable of dimming. The driver determines the low-end light level and the best possible dimming performance.

“It is the driver’s job to properly interpret the control instruction it is receiving and then adjust the power output to the LED in a stable and controlled manner,” Biery said.

Control factors

LEDs can be controlled in two ways, according to Tumula. The first, pulse width modulation (PWM), switches the LEDs on and off very quickly, so they appear dim to the eye. The number of on/off cycles determines the dimming level. The other method—current reduction—reduces the amount of electrical current flowing through the LED, so it produces less light.

When controlling LEDs, one of the most important factors to consider is the client’s ultimate needs, which will drive the contractor’s specifications.

“Dimming range is typically very important to end-users, and it needs to be tailored to the specific application,” Angel said. 

Contractors should remember that, since incandescent lamps dim well below 1 percent perceived light, that orange filament glow they produce has set the expectation for all dimmed light sources. However, the dimming range of an LED lamp or fixture can vary greatly from one device to another.

“The most important consideration is that the LEDs not produce flicker whey they are dimmed, which depends entirely on the LED driver,” Tumula said. 

If the driver controls the LEDs through current reduction, it must deliver stable and clean electrical current with smooth reduction over the entire dimming range. If the driver controls the light with PWM, it has to switch the LEDs at a frequency higher than the human eye or video recording equipment can detect, which is typically above 1 kilohertz.

“Dimming below 10 percent light output typically can only be achieved with the PWM method,” he said.

End-users and contractors also should ensure that the dimming control is rated for use with the chosen LED light source. 

“When people try to use LEDs with an incandescent dimmer, they find that they have issues, such as limited range, nonsmooth dimming movement, and small flickering, fluttering or other effects,” Lombardi said. 

Lighting control manufacturers, however, post their latest performance pairing tables to help end-users or contractors choose the correct dimmer model for the lamp.

“These tables are the result of testing a broad range of manufacturers’ lamps, and the information is regularly updated,” said Jay Sherman, director of marketing, Leviton’s residential business.

Standard protocols

The three protocols that electrical contractors should be most aware of, according to Biery, are NEMA SSL-7, 0–10V dimming, and digital control methods such as Digital Addressable Lighting Interface (DALI).

NEMA SSL-7A 2013 Phase Cut Dimming for Solid State Lighting provides compatibility requirements when a forward-phase cut dimmer is combined with one or more dimmable LED light engines (LLEs). An LLE comprises one or more LED modules, LED control gear, and a connection to the main circuit. It is intended to be forward-looking and to be used to design and qualify dimmer and LLE products for use with each other. It is not intended for use to determine compatibility with existing products or the installed base of LLEs and phase cut dimmers.

The 0–10V dimming protocol is the default option for fixture manufacturing today. It is inexpensive, analog-based and “is more of a compatibility than a performance standard,” Biery said. 

Zero volts equals the lowest dimmed level, and 10V equals no dimming or full light output.

DALI is a worldwide standard, specified by the International Electrotechnical Commission (IEC) and is set out in the technical standard IEC 62386. DALI guarantees compatibility and allows equipment from different manufacturers to be connected together.

“DALI enables bidirectional digital communication between the control system and the LED driver or fluorescent ballast and is used where a more sophisticated and individual fixture control is required,” Tumula said.

Zigbee, Z-Wave and EnOcean are examples of wireless communication protocols that describe the signal that travels between the lighting control and the fixture.

“The challenge to any wireless protocol, even presuming the controller and fixture are compatible, is making sure the wireless signal is reliable,” Biery said. 

Contractors engaged in projects that use any of these protocols need to work with IT staff to ensure that there are sufficient repeaters and signal boosters to create a reliable control signal. As these technologies get adopted more regularly in the industry, fixture retrofits and control will become easier.

“Contractors can benefit from today’s innovative LED power supplies that offer an unprecedented range of customizable settings and features that simplify meeting design requirements,” Tumula said. 

Using the latest in programmable LED drivers can also help give a contractor a competitive advantage and secure more business by helping them increase flexibility and meet individual customer needs.

“Going forward, the industry will see tremendous advances in ways of controlling lights through communication protocols and smart devices,” Grande said.

About the Author

Darlene Bremer

Freelance Writer
Darlene Bremer, a freelance writer based in Solomons, Md., contributed frequently to ELECTRICAL CONTRACTOR until the end of 2015.

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