Tuesday, July 19, 2011

Radio interference from LED lighting

High-power light emiting diodes (Luxeon, Lumiled)
Image via Wikipedia
Interference reports suspecting LED lighting products, emitting electromagnetic energy, causing problems with VHF radios and other receivers are nothing new, just do a Google search and you’ll find complaints of such problems. These complaints are few and scattered, possibly due to the lack of mainstream adoption of LED lighting, but that is all about to change.

Many regions have, or are adopting, rules aimed at reducing waste from lighting products, from toxic substances such as mercury, as well as overall power consumption reduction of lighting products. A growing trend around the globe is the general phase-out of incandescent bulbs.

While CFLs (Compact Fluorescent Lamps) are far more efficient in terms of power consumption than traditional incandescent lighting, like all fluorescent lights, they contain mercury, a toxic substance, thus complicating disposal and presenting an environmental hazard.

An alternative to CFL is LED lighting, or Light Emitting Diode. Newer LED technology has the benefit of much lower power consumption compared to traditional lighting, as well as the reduced environmental impact, and, compared to several years ago; they are becoming increasingly more affordable. It has been stated that more than 50% of our electricity consumption for lighting would be saved if the efficacy reached 200 lm/W (lumen per Watt). LED efficacy reached 100 lm/W in 2010, and continuing the trend, they will easily hit the 200 lm/W mark by 2020 as predicted. Some companies claim that they have already attained this level of efficacy.

However, although today’s LEDs are capable of long life, and delivering high light output levels with very little power consumption, most need to be paired with a drive circuit to provide constant current sourcing to operate in our homes and offices, and that’s where the problem comes in. These switching drive circuits operate at increasingly higher frequencies, and in order to maintain the highest efficiency, and highest LED longevity possible, they also need to maintain very high slew rates. These factors contribute to the overall unwanted emissions from each individual lighting element, increasing the Electromagnetic background noise.

Electromagnetic Interference or EMI mitigation inevitably increases the overall cost of products by adding additional components to a design, or requiring a more complicated and expensive design and layout, and for low price consumer electronics, with very small profit margins, every penny counts. As EMI mitigation is considered by some as an unnecessary expense, it is often overlooked or simply disregarded. Proper operation and safety concerns also make engineering a quiet design more difficult and expensive. So the cheaper LED lighting will potentially be the most problematic in terms of interference, but they will also be the preferred choice for the average consumer, and therefore the most prevalent.

Couple the added costs with the lack of regulatory enforcement and oversight governing the EMI of these devices and you can see the potential problem this poses. Most of the interference may be caused by very high frequency emissions, typically in the 30 – 300 MHz range, and possibly higher.

In the US, most products capable of causing interference that may be used in the home and office fall under FCC Part 15 rules governing the amount of unwanted electromagnetic energy that products can produce, both conducted on the power lines, and radiated from the products themselves, to prevent interference to radio receivers and for the overall protection of the radio spectrum. For most products, compliance with these rules however is primarily based on the honor system, and requires that manufacturers be knowledgeable in the application of the rules and proper test methods. Common misinterpretation of the rules, may lead manufacturers of LED lighting to address only the lower frequency conducted disturbance, or possibly to consider themselves exempt from the rules altogether. This may only be addressed by the FCC when problem reports become widespread.

Europe has addressed, and continues to monitor, some of these issues, with the amendment of standards covering lighting product emissions, such as EN 55015:2006, adding emission measurement requirements from 30-300MHz. Confusion may still exist on the proper application of the harmonized standards, possibly leading to improper evaluation of electromagnetic emissions, and it’s questionable if the frequency range is high enough to cover some products found on the market today.

In New Zealand, a report issued in the summer of 2010 warns of the potential interference that LED lighting products could pose, and urges reports of any interference problems to the Radio Spectrum Management.
As LED lighting products enjoy mass adoption, it is possible that mysterious failures of everyday things we have come to depend upon such as remote controllers, baby monitors, radio receivers, garage door openers, security systems, just to name a few, may be just around the corner. This doesn’t need to be the case however, as the problems are preventable with careful consideration and a desire to do so.