Reducing RFI at Home From Lighting Fixtures?

amper asks: "I'm in the process of building a new home recording studio. When I originally moved into my new (very old) house, I decided that in the interests of conserving energy, I would replace most of the incandescent lighting fixtures or lamps in my home with fluorescent fixtures or compact fluorescent replacement lamps in those fixtures which could not easily be replaced. Unfortunately, these fixtures are creating a massive amount of radio frequency interference in my home. The worst culprits seem to be the dimmable fluorescent fixtures in my living room. Barring replacing all my fixtures and lamps with conventional incandescents, can anyone point me in the direction of alternatives? Is it possible that the decreasing quality of most home goods has led to a decreasing quality in fluorescent ballast systems that are much more noisy from an RFI standpoint? Some of these fluo's are so noisy, they even emit audible sound! It's gotten so bad that I can't even play an electric guitar without turning off all the non-incandescent lighting in my house, which pretty much limits me to playing and recording during daylight hours (when I'm supposed to be out making money)."

Comments

Focus on ground loops, not on RFI sources.

[hankwang]

I come from a physical laboratory where we have to measure small signals with an acceptably low noise despite the presence of laser flash lamps, or even high-voltage discharges in more or less open air. The best way to avoid RF interference is not to remove all RF sources, but to design the electronic circuits correctly.

The main thing that makes electronic circuits sensitive to noise is ground loops. Often, signals travel through cables that have two wires or a central wire with a shield surrounding it. Normally, equipment (whether it is an oscilloscope or consumer-grade audio equipment) has a common ground, which means that the neutral wire of each and every input and output is connected. If you have more than two pieces of equipment interconnected, it is likely that there are loops in the ground wire, for example the cable from mixer to some effect generator, and the wire back. All these loops acts as antennas that can pick up noise. Having shielded cables doesn't help because it is the shield, that acts as ground wire, that causes the problems.

The first and simple step is to have all wires bundled as close together as possible, such that the area inside the loops is as small as possible. The next step is to upgrade your equipment to stuff that has balanced inputs, with those big XLR connectors. Here the shields are really shields against RF interference, while the signal is carried by two wires inside the shielded cable. Balanced signals means roughly that the equipment measures the signals on the two signal wires completely independent from the ground.

Re:Focus on ground loops, not on RFI sources.

[rhild]

To expand on that, any RF noise that gets into the cable will appear in phase on both signal conductors, which will result in it being cancelled out in the input circuit of the device the cable is feeding, if the device has balanced inputs.

CMRR (Common Mode Rejection Ratio) is a measure of how well an input circuit cancels out this kind of noise. When looking at the specs for gear this is one of the important but often overlooked numbers to check out.

RFI Solutions

[Ed Almos]

As a radio ham I have similar problems, try the following.

1) You can get ferrite rings of various diameters. Try winding a couple of turns of the cord leading to the light through one of these rings. The ring should be as close as possible to the fixture.

2) Wire RF chokes in series with the fittings. These work in a similar way to the ferrite rings but are more effective.

3) It's possible to obtain capacitors that are rated for 110/220 volt operation. Have a look inside a PC power supply and you may see one, they are normally encased in yellow transparent epoxy. Wire one of these across the fitting.

And finally.........

4) Ask for help from the right people. Try and find either a local radio ham or (even better) a local ham club. These guys will be experts at fighting RFI and will help you out.

Ed Almos
Budapest, Hungary

Ditch the dimmers.

[david.given]

Trying to dim fluorescent lamps is a really problematic process; see here for a discussion. You can't dim them by reducing the voltage, and have to pulse the power supply instead. This will, as you have discovered, interact oddly with the ballast and the tube itself and is probably what's making the bulk of your radio noise.

(The article mentions a number of problems, including the fact that you might be significantly reducing the lifetime of your tubes by dimming them. YMMV.)

What I have in my living room are some long-live fluorescents to provide the bulk of the light, and some incandescents to change the colour and make the illumination more interesting. You might be able to do something similar without having to hook the tubes themselves up to the dimmer.

Re:Flourescent lighing

[DAldredge]

he following introduction is from a publication by the National Electrical Manufacturer's Association (NEMA) entitled "Fluorescent Lamps and the Environment". This publication and a lot more valuable information can be found at the NEMA website devoted to proper lamp disposal called www.lamprecycle.org. An Adobe Acrobat PDF version of the publication can be downloaded from www.nema.org/lamprecycle/nemafluorfinal.pdf

If you need more information about properly disposing of lighting waste click on the link at the left for "lamp disposal rules".

Why Do Lamps Need Mercury?

"Mercury is an essential ingredient for most energy efficient lamps. Fluorescent lamps and high intensity discharge (HID) lamps are the two most common types of lamps that utilize mercury. Fluorescent lamps provide lighting for most schools, office buildings, and stores. HID lamps, which include mercury-vapor, metal halide, and high- pressure sodium lamps, are used for street lights, floodlights, and industrial lighting. A typical fluorescent lamp is composed of a phosphor coated glass tube with electrodes located at either end. The tube contains mercury, of which only a very small amount is in vapor form. When a voltage is applied, the electrodes energize the mercury vapor, causing it to emit ultraviolet (UV) energy. The phosphor coating absorbs the UV energy, causing the phosphor to fluoresce and emit visible light. Without the mercury vapor to produce UV energy, there would be no light. A four-foot fluorescent lamp has an average rated life of at least 20,000 hours. To achieve this long life, lamps must contain a specific quantity of mercury. The amount of mercury required is very small, typically measured in milligrams, and varies by lamp type, date of manufacture, manufacturing plant, and manufacturer."

"If lamp life is shortened, more lamps must be purchased to achieve the same length of service, and the number of lamps that generators must dispose will increase. How Much Mercury Do Lamps Contain? Based on a 1999 NEMA survey, the average four-foot fluorescent lamp contains about 11.6 milligrams (mg) of mercury. This number has been steadily declining as lamp manufacturers work to reduce mercury content to the minimum amount technically feasible without reducing lamp life. The average four-foot lamp today contains over 75% less mercury than the same lamp would have contained in 1985. According to the U.S. EPA, total global natural and manmade emissions to the environment are 5,500 tons. 1 Manmade sources in the U.S. released 158 tons of mercury in 1995. For comparison, all of the lamps sold in the United States in 1999 containonly an estimated 13 tons of mercury, of which only a fraction will be released as an air emission. Proper lamp disposal or recycling will result in keeping almost all of this mercury out of the environment."

I guess you've never toted them up.

[Engineer-Poet]

I use a bunch of circle-tube CF's installed in table lamps. They are rated at roughly the same light output as a 150 W incandescent but they use only 34 watts on full (they're 3-way). They will run at least a year between tube replacements and these units cost about $20 new. Figuring 2000 hours of operation @ 34 watts and 8 cents/KWH and $20 up-front, the total cost for those 2000 hours is $25.44. That's assuming that you have to throw away the whole lamp after 2000 hours instead of just replacing the circle tube; if you replace the tube every 2000 hours at $5 each the cost for each incremental 2000 hours goes down to $10.44.

Lifespan of a 150-watt incandescent is what, 200 hours or less? Figuring 10 bulbs at $1 each plus 300 KWH of electricity @ 8 cents, the same 2000 hours of light would cost $34. Looks like your approach is penny-wise, pound-foolish.