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Stopping EMI from Fluorescent Lights and Ballasts

Stopping EMI from Fluorescent Lights and Ballasts

Any time you deal with electronics, specifically anything with long wires or a transformer, you’re going to run into electromagnetic interference (EMI).  But what is EMI exactly?  In short, EMI is any electrical signal (a voltage or radio frequency (RF) signal) that interferes with other electrical devices; especially those relating to communications equipment (think cell phones or handheld radios).  This has become more of a problem since electronic ballasts have replaced more and more of the traditional magnetic ballasts.  Electronic ballasts are more efficient, quieter, and promote longer lamp lives, but they emit much stronger EMI fields than traditional magnetic ballasts.

Causes of EMI

EMI is caused by one device inducing voltage (generating a discrete voltage without a direct electrical connection) within a second component.  Induced voltage occurs when devices are not properly shielded, are laid out improperly (e.g. coiled around objects or run parallel for the entire distance), use high frequency AC voltage, or are grounded improperly.  Because ballasts typically generate a humming or buzzing noise – electronic ballasts are quieter than traditional magnetic ballasts, but the hum still exists – remotely mounted ballasts are sometimes preferred.  Remotely installed electronic ballasts generate substantial amounts of EMI due to their higher operating frequencies (magnetic ballasts operate at 60 Hz while electronic ballasts are typically operated at 20-60 KHz, that’s 50 to 200 times greater).  If the connection cables are unshielded, the high frequency will convert the cables into a powerful antenna, creating an electromagnetic field that can affect radios, Wi-Fi connections, and cell signals.  In a fluorescent system, the fluorescent lamp itself is capable of radiating electromagnetic waves at frequencies of 10 KHz to 100 MHz depending on the electronic ballast connected to it.

[ctt title="Fluorescent Ballasts can cause both conducted EMI and radiated EMI!" tweet="Fluorescents can cause conducted and radiated EMI, here's how to stop it! #Ballasts #EMI stopping-fluorescent-ballast-emi" coverup="0ezwP"]Regardless of cause, EMI is generated in two forms: conducted EMI and radiated EMI.

  • Conducted EMI – interference added to the local power network of interconnected devices that do not necessarily share a direct power or signal source.
  • Radiated EMI – generated electromagnetic fields inherent to electronic devices. Typically associated with solar flares.

The simplest way to remember the difference is that conducted EMI is generated by physical contacts, while radiated EMI is radiated through the air.

Identifying EMI Sources

If you’re seeing signal noise, static, loss of signal or any other kind of signal interruption in wireless devices (or even in line-connected audio equipment such as intercoms), then you likely have a problem with electromagnetic interference.  To identify the source, deactivate all electrical sources.  This means turning off lights and communications equipment.  Then listen to the interrupted device.  In the case of a radio with severe static, turn everything else off and listen to see if the static persists.  If no signal noise is present, then one or more devices are generating the EMI.  To find the offending piece of equipment, leave the susceptible device active and turn on each system individually until the signal noise returns.  If the signal noise does not return, it is likely a cumulative effect of multiple devices.  Turn on multiple likely offenders (compare to the offending issues in the previous section) such as ballasts, fluorescent lamps, or any device that generates RF or microwaves to identify which sets of components are generating the offending field.

Mitigating EMI

While electromagnetic interference has no negative effect on plants, animals, or people, it negatively impacts other electrical equipment and day-to-day devices; the constant search for a cellular network signal, for example, will quickly drain a cell-phone battery.  Properly installed systems should not generate intense EMI, which means that resolutions to interference problems should be simple.


Ensuring proper ground connections for all electrical devices will shunt high frequency interference to an earth ground or common.  If grounding is not done properly, cables, grounds, or electrical equipment can act as a very powerful antenna, radiating out a strong EM field.  Grounding the fixture and ballast to a common earth ground will help prevent this from occurring.


The length of wire leads between source and device should be as short as possible.  Since this is not always possible in the case of remotely mounted ballasts, twisting cables together will help to cancel out the EM fields generated by long runs of cable.  Using cable turns with paired power cables or input leads will generate opposing induced currents, minimizing or removing EMI generated by the runs.  You should also avoid large loops or wire bundles, either of which will act as an antenna.

Shielding and Filters

Additional components can be used to block or absorb EMI caused by other equipment.  Cable runs should be placed in metal conduits, and fluorescent or HID lights can be housed in luminaires with copper mesh or conductive glass to shield against EMI generated by the cables or lamps.  All exposed conductors should be shielded.  The conductive material of the shielding will absorb the EM field and prevent radiated or conducted EMI.  Additionally, EMI filters or ferrite cores can be placed on ballasts, power conductors, and cabling to reduce conducted EMI across the length of the cable.

Additional Methods

Simple alternatives, such as relocating the susceptible devices (e.g. moving a radio outside of the generated EMI field) are also feasible.  Changing or replacing the fixture design, using an alternative ballast, reducing lamp wattage, reducing the inductive or capacitive load (or a ballast’s lamp load), or changing the layout of grounded components are all viable methods for reducing EMI within a system.

EMI EMF Reduction Guide
EMI EMF Reduction Guide

FCC Regulations

The Federal Communications Commission (FCC) regulates radio and wire communications within the US for devices with conducted emission frequencies between 450 KHz and 30 MHz and radiated frequencies from 30 MHz to 960 MHz.  Since most ballasts and fluorescent light systems fall well below these ratings, they are not regulated by the FCC.  Any products that meet the requirements set by the FCC will be clearly marked.  No single device that is capable of generating a significant amount of interference is legal for sale in the United States.

The majority of fluorescent or electronically ballasted lights will not generate a large enough EM field to interfere with your devices; however, an improper setup or multiple systems in a large room (e.g. a grow room or office space), can easily reach noise levels capable of blocking wireless signals.  Knowing the cause of the problem, and how to deal with it, are essential for the wireless world we live in.  If you have any extra questions or problems with EMI, ask them in the comments below.  As always, you can contact or stay up to date on our newest articles just by following us on FacebookTwitterGoogle PlusLinkedInPinterest, or Instagram.

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Lighting in the News - May 2015

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