[RFI] Updates on CFLs & LEDs

dalej dj2001x at comcast.net
Sat Jan 22 03:06:29 PST 2011


Dale,

I've got quite a few CFL's here also and have not found them to be a RFI producer yet.  I had one out in the garage which did interfere with a wireless intercom that used the power line for the communication line.  Whenever that CFL was on the intercom was not useable.  I have two CFL's in my shack luxo lamps right above the rigs and they are RFI quiet.  They are turned on for hours at a time so they save quite a lot in electricity.    

Your idea of marking the CFL's is a good one.  I will start doing that too.

73
Dale, k9vuj




On 21, Jan 2011, at 13:55, Dale Svetanoff wrote:

> Fellow RFI/EMC folks,
> 
> I thought I'd provide some update information on two oft-discussed topics on this reflector: CFLs and LEDs.  Here goes.
> 
> First, I just purchased a set of 5 CFLs to relamp the light bar in my master bedroom bath.  I had 5 conventional 60 watt "globe" lamps in there that have worked well for the purpose, but not only do they suck up 300 watts of energy, they deliver just as much heat.  Over the past 3 or 4 years, I have replaced many standard bulbs with CFLs of varying lumen ratings and been mostly happy with both performance and CFL life.  I have had zero RFI issues.  My chief reason for installing CFLs is to reduce heat load on the A/C system in warm weather, with reduced power consumption running a close second.    
> 
> I mention these 5 lamps because of what they are and what the manufacturer says about them.  Please take note:  The bulbs are marketed by Feit Electric of Pico Rivera, CA.  They are called "Ecobulb Plus" and are listed as 60 watt equivalents, drawing 15 watts, delivering 800 lumens, with an estimated life of 8000 hours.  (These specs are for each bulb.)  The home use warranty is for 2 years, and the cost was $4.88/each.  A prominent note on the side of the box discusses "Proper CFL Usage".  I quote: "Globe-shaped covered twist CFLs are best suited for fixtures that are left on for 15 or more minutes at a time."  The rest of the statement deals with airflow, no use of dimmers, and so forth.  I typically run those bathroom lights for about 30 minutes at a time at least twice per day.  A small print notice on the bottom of the box says that "this product complies with Part 18 of FCC rules but may cause interference with radios, televisions, wireless telephones and remote control
> s."  Note that Part 18 addresses ISM devices, which does include intentional emitters.  I presume that the reference to remote controls is to RF-type remotes, as opposed to the more common IR ones.
> 
> This is the first time, in my CFL-buying experience, that I have seen a manufacturer actually state the recommended operating conditions on the bulb packaging.  I've checked my other in-stock bulbs, and no, none of them make that statement.  I have saved my sales receipt and the proof of purchase for each bulb, just in case they don't last 2 years in my application.  I might add that my normal routine with new CFLs is to use a fine-tip marker and place the date of first use on each bulb (near the base, so that if it dies early, I'll know.  (I have a CFL flood lamp that was installed on 1-31-09 and died on 8/20/10.  The 3 others I installed at the same time are still running.)  As for RFI, I don't expect any, but then again, I'm not usually running those lights while operating.  
> 
> A final CFL note: I ran a test this morning that I should have run long ago, but just never found the round-tuit.  I have a Teac AM-FM tuner in the family room as part of my eclectic stereo system.  (It's a blend of ancient and modern components, with the heart being a Dynaco PAS-2 pre-amp fresh from the 60's.)  The AM part of the tuner uses a factory-supplied wire loop antenna (no ferrite core) that is mounted on a hinge so that the user can pivot the loop (in a vertical plane) to adjust for best reception.  Now that my power line issues are gone (for the moment, anyway), I can enjoy "armchair" listening to the major Chicago AM stations that are located about 150 miles or so to the east.  I first tuned in WBBM-AM on 780 kHz and noted usual band noise, but no significant arcs or buzzes.  I then switched on the 2 separate groups of CFLs (in ceiling fixtures) which light the shared area that includes both the family room and the kitchen (divided by a breakfast counter).  No cha
> nge to what I heard.  Then I switched on the wall plate dimmer that controls the set of 4 incandescent bulbs (3 @ 40 watts and 1 @ 60 watts) hanging beneath the family room ceiling fan.  Aaahh - that familiar old buzz-saw sound!  I might add that the dimmer, which was installed by the builder's electrician, is rated as having an RFI filter!  Bottom line: the CFLs are "clean" enough for AM BC band use.   
> 
> Quick note on LED lights:  I recently received an interesting booklet from Digi-Key under their "techzone" magazine name.  The publication appears to be partly sponsored by Cree Technology, a major maker of LEDs and related systems.  There are several articles within dealing with the major topics related to LED lighting technology, including power supplies, thermal issues, and achieving color balance.  I am not quite certain how I got this copy sent to me, I strongly suggest that anyone interested try contacting Digi-Key to see if you can get one for yourself.  
> 
>> From the RFI perspective, one of the more interesting articles was contributed by National Semiconductor and is entitled "Driving LEDs: To Cap or Not to Cap".  Huh?  Well, what the title refers to is to use (or not use) capacitors on the output side of the switching power supply that is integral to LED lamp array operation.  Not surprisingly, LEDs work best with constant CURRENT power sources, and the article talks about the design of buck-type converters that deliver constant current performance AND which offer dimming control!  Here is the catch:  you can not dim the LEDs using the wall plate dimmers as discussed above in the CFL discussion.  The dimming control signal must go directly to the pulse width modulator ("PWM") ship in the power supply.  If output caps are not used, the limiting factor in the buck converter design becomes the series inductor, and that allows more precise control of brightness than if there are filter caps after that inductor.  So, where are thes
> e LED dimmers used?  In products, such as displays, not in general lighting.  The article also mentions that typical operating frequencies for these buck converters are in the range of 50 kHz to 2 MHz.  
> 
> Hope these comments help.  Disclaimer:  I have no financial interest in any product or supplier mentioned.
> 
> 73, Dale
> WA9ENA                 
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