Make sure the LED luminaire you choose is a "Sleeping Beauty"

July 30, 2007
Some LED luminaires draw current even when there is no emission, which reduces efficiency and negates one advantage of the technology, reports Brian Owen.
The issue of offline or standby power has been observed in some LED luminaire products, following testing by the US Department of Energy (DoE) commercial product testing program.

In conventional lighting, typically a light has a switch that places the light on or off, through which no current will flow in the off position.

“Solid-state lighting is not as cut and dry,” says Scott Riesebosch, president of Canada-based CRS Electronics (, an LED light engine designer and manufacturer. In electronic systems that have quick start-up facilities or remote controls, much like old non-ENERGY STAR compliant computer monitors and TVs, the electricity is still flowing.

“LED is a hybrid of lighting and electronics technology, and as the result you are incorporating the positives as well as the potential negatives of each technology,” says Riesebosch. “If designed properly, energy is minimized to an acceptable level and the LEDs and the micro-processor are essentially put to sleep.”

“The analogy is much similar to the ENERGY STAR-compliant computer monitors that require only minimal power to restart. Not looking at this issue is like parking your car and leaving the engine idling unnecessarily to listen to your stereo,” added Riesebosch.

Proper design of LED luminaires allows for more efficient operation. If the constant use of minimal power is not for a specific purpose, such as intelligent systems, including addressing modules, dimming or occupancy sensing, it is the result of poor design.

LED drivers have an inhibit (shutdown) input, typically putting the driver to sleep. Drivers designed with discrete components rather an integrated solution with an inhibit or shutdown input that puts the entire driver to sleep, are typically less efficient. They are also less reliable and harder to produce. The rationale may be a reduced production cost. Buyers beware if your motivation to employ LED technology is energy reduction.

At the recent DoE-sponsored SSL Market Introduction Workshop, "Voices for SSL Efficiency" held in Boston on July 16th and 17th, Jeff McCullough, Senior Research Engineer at the DoE’s Pacific Northwest National Laboratory (PNNL) (, reviewed the results of the commercial product testing program and presented the Final Draft of the new proposed ENERGY STAR criteria for SSL.

"With respect to offline or standby power, proposed ENERGY STAR compliance will prohibit offline or standby draw, with the exception of intelligent systems and then only to a maximum of 0.5 watts in standby mode," said McCullough.

"The primary issue found with the products tested was the use of in-line power supplies and placing the switch on the load side versus the line side," he added. "Simply making this change would solve the problem in the products tested."

Riesebosch cautions luminaire developers "to not overlook the efficiency of the driver. Part of the appeal of LED lighting is the overall system energy reduction. If you employ efficient LEDs, efficient optical design, but an inefficient driver, you have negated one of the most important advantages of LED."