White LED Control

The U.S. Department of Energy (DOE) predicts that solid-state lighting will achieve efficacies as high as 160 lumens per watt and provide most of our general lighting needs within the next 20 years, thereby reducing the nation’s energy costs by 6–7 percent.

That’s not counting lighting controls, which already can reduce lighting energy consumption by 50 percent in existing buildings and by at least 35 percent in new construction, according to the New Buildings Institute.

Combining solid-state building illumination, such as light-emitting diodes (LEDs), with intelligent, automatic controls in the future will produce spectacular efficiencies. Today, however, controlling white LED products in architectural lighting applications can be a chal-lenge.

Some products have a driver and power supply that enable dimming; others don’t. Many are proprietary and incompatible with products from other manufacturers. Some don’t work with basic electronic thyrister- or triac-based sensors and relays. Some don’t work well when connected to standard dimmers or existing 12-volt (V) electronic transformers.

Kevin Willmorth, principal of Lumenique LLC, Germantown, Wis., said electrical contractors designing lighting and control systems featuring LED products should verify that all components on the job are compatible and supported by their manufacturers. Additionally, the component combinations should be tested to ensure they will work as specified, he said.

Future potential for LED control, however, is positive. LEDs are ideally suited for lighting control in a number of ways.

LED lighting, for example, is friendly to switching. LED, can be controlled using both manual switches and automatic switches, such as occupancy sensors and photocontrols. LEDs turn on and achieve full brightness instantly, and frequent switching does not affect lamp life, unlike fluorescent and HID lamps. However, be sure to avoid low-end occupancy sensors and photocontrols that may not work well with LED devices.

LED lighting is also very friendly to dimming, Willmorth said. Like fluorescent dimming, a dimming range is available from 1–100 percent, depending on desired capabilities and acceptable cost. The highest-performing products dim smoothly from 1–100 per-cent, while the lowest dim from 20–100 percent while exhibiting an inconsistent step-dimming effect.

Unlike conventional fluorescent dimming, such as 0–10V DC, which experiences a degradation of efficacy accelerating toward the low end of the dimming range, LEDs produce light output that is proportional to electrical input. An LED operating at 80 percent of its initial rated power will produce roughly 80 percent of its initial rated light output. Toward the low end of the dimming range, however, a remarkable reverse effect occurs—efficacy actually increases. This is because LEDs are very sensitive to internal tempera-ture, and as they are dimmed, temperature drops, resulting in an increase in light output. This is good for energy management, but for manual dimming, it means light output and dimmer setting may drift out of proportion at the low end of the dimming range. Some higher end products compensate for this.

A reduction in thermal stresses on LEDs due to dimming can have other positive effects, Willmorth said.

As noted above, reductions in LED internal temperatures will increase light output. Since service life with white LED products is based on light output—with useful life defined for general lighting application as the point at which the light source is emitting 70 percent of its original light output—dimming can increase LED service life. Additionally, high operating temperatures can cause a color shift to-ward blue among most white LEDs as their phosphors fail. By reducing temperatures, this color shift can be delayed.

When dimming—or the ability to integrate the LEDs into a centralized control system—is desired, special LED drivers and power supplies are typically necessary, Willmorth said. The driver regulates current flowing through the LED devices just the way a ballast regulates current flowing through a lamp. Sometimes, the driver and power supply are integrated into a single product. These devices can be mounted remotely from the LEDs. The driver is the point of connection between a LED lighting system and its controller. Light-ing and controllers can be connected through 0–10V DC analog (typical for white LEDs), digital (developing for white LEDs) or DMX512 (typical for color LEDs) communication methods. When selecting 0–10V DC controls, note that not all controls definitively shut off the power in the off state, and it may require a separate switch or relay to do so.

For retrofit, there are line-voltage AC LED products that do not use driver circuits or power supplies and work directly on 120V AC power and with existing dimmer controls that are rated as compatible by the manufacturer (but, beware of flicker). Additionally, 12V AC products are available that operate with dimmable 12V AC transformers (but ensure the transformer is compatible with other con-trols and sensors).

DILOUIE, a lighting industry journalist, analyst and marketing consultant, is principal of ZING Communications. He can be reached at www.zinginc.com.

About the Author

Craig DiLouie

Lighting Columnist
Craig DiLouie, L.C., is a journalist and educator specializing in the lighting industry. Learn more at ZINGinc.com and LightNOWblog.com .​

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