RF emissions from energy efficient fluorescent lighting
Conventional tungsten filament lamps are entirely without radio frequency emissions, except in rare fault conditions. However, because they are inefficient, the UK government is promoting use of energy efficient alternatives in support of its climate change policy. These include energy efficient fluorescent lamps, which produce high levels of RF interference.
For a fluorescent tube to operate at high frequency an electronic switching ballast is required. A typical operating frequency for an electronic ballast would be in the region of 20kHz to 40kHz. The high frequency ballast is essentially a switching power supply and has the potential for radiofrequency interference in the same way as any switched mode power supply. Dimming is achieved by reducing the power applied to the fluorescent tube. In order to maintain the discharge, the frequency of operation must increase as the light output level is decreased. Thus a typical electronic ballast which operates at around 30kHz for maximum light output will supply the lamp at increasing frequencies up to approximately 100kHz for minimum light output.
Measurements of sample lamps have shown that electronic ballasts can cause an increase in interference in long wave and medium wave bands to portable radio receivers. The minimum distance of a radio receiver to the lighting samples for good reception varied between samples. Of particular interest was the interference to AM services from the dimming ballast. Because the fundamental ballast operating frequency alters as the lamp is dimmed, so interference to individual radio stations depends upon the light output level of the unit. For example at maximum dimming (minimum light output) the second harmonic of the lamp operating frequency fell at the same frequency as BBC Radio 4 Long Wave (198kHz) and so reception of this station at maximum dimming was considerably worse than the reception for other long wave stations.
Moreover, VHF band 2 FM radio reception can be affected by electronic ballasted fluorescent lamps with batten type fittings. Modern lighting technologies and techniques do give rise to significant emissions in the VHF band. In practice these emissions are seen to be limited to an upper frequency of less than 300MHz at present, but since the EMC standard for lighting (CISPR 15) gives no tests above 30MHz, these emissions are effectively uncontrolled by any legislation.
Switching power converters are a frequent source of RF emission problems, and those used in lighting products are no exception. In this case, the problem is compounded because fluorescent lamps are found in large numbers in many buildings and it is hard to find a location far enough away from them; and the price pressure on such products works against best practice in design to minimise emissions. Because of their dimensions, batten-type fittings will radiate effectively at VHF, and efficient switching ballasts will quite cheerfully generate energy at these frequencies. Since (at present) the relevant standards give no protection above 30MHz, the pollution is likely to get worse as more and more energy-efficient but RF-polluting lamps are installed.
References and links
Development of improved test methods for assessing the EMC emissions from luminaires and ancillary devices, York EMC Services, Radiocommunications Agency Project AY4125, March 2002: available from http://www.radio.gov.uk/topics/research/topics.htm#emc/
Microwave-powered light bulbs could stop satellite broadcasts
Sirius Satellite Radio Inc., is complaining that the microwave powered bulbs manufactured by Fusion Lighting Inc., will directly interfere with satellite radio broadcasts. Their year-long battle has seen them engage in debate before the Federal Communications Commission (FCC), a private testing laboratory in Columbia, MD, and in the near future, it appears, in courtrooms in Texas and Maryland.
Fusion says that it’s now about a year away from commercial sales of the bulbs for use in lighting applications as diverse as gas stations and airport runways. The lights invoke the prospect of highways being lit up at night by hundreds of microwave bulbs which could, claim their opponents, affect the satellite broadcasts assigned to the same frequencies.
Even a small amount of accidental ‘leakage’ from electronic devices can be a problem if it occurs at the same frequency as a satellite downlink, because the signal strength at the satellite receiver is very weak.
When the ‘leaky’ devices are intended (as these are) to be used in their thousands over large geographical areas, two problems arise… firstly, there is a greater chance that one or more of them will be near to a satellite receiver, and secondly the ‘ensemble effect’ of the emissions from a large number of devices can have a stronger effect on a receiver than any of the devices on its own.
References and links
“Bulb manufacturer light up spectrum wars”, Conformity, Vol. 6 No. 10, October 2001, ‘News Breaks’ section. http://www.conformity.com