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LED Bulbs, RF Noise, and a Crazy Idea

Carol and I were in Costco last week, stocking up on consumables (everything from toilet paper to Hoody’s Peanuts) when we spotted something that made me do a double-take: a package of four Feit LED dimmable 60W equivalent light bulbs for $10. I’ve never seen them for less than twice that. We grabbed a pack to try at home, because our new house here contains a lot of 60W bulbs.

How much of a lot? There are nine Hampton Bay ceiling fan/lamp fixtures, each holding three 60W bulbs. (We found later that the fixture over the dining room table had three 75s in it.) That’s 27 bulbs right there, plus another twelve or fifteen in bathrooms and outside light fixtures. Figuring 40 60W bulbs, that’s 2,400 watts. Granted, not all of them are on at once, and several fixtures (like the one in the guest room and the two outside on the patio) are rarely on at all. However, there are another eighteen 65W ceiling floods, so I’m guessing our typical evening use is about 2,500 watts overall. It adds up. If bulbs are now as cheap as Costco was offering them, I was ready to jump.

A sidenote: There was some sort of utility company instant rebate, so the register price was about 1/3 less than the package price. Outside the Phoenix area, your prices may (and almost certainly will) vary.

This being Arizona, there was a thick layer of brown dust (over and above the dead bugs) on the lamp globes and on the existing bulbs themselves. We ran three loads of lamp globes through the dishwasher because their spatter finish tears threads off the ScotchBrite pad by the sink. I put three bulbs in the fixture in Carol’s office, then stood back to gauge the quality of the light.

Marvelous! Three $2.50 LED bulbs gave brighter and slightly whiter light for a total power draw of 28.5 watts. We went back to Costco and bought 24 more, plus a test pack of 65W equivalent LED ceiling floods. I spent a day on a ladder swapping out bulbs, and although the ceiling floods aren’t all done yet, we’re looking to cut our lighting power draw to 1/6 of what it would be on incandescents.

This isn’t all about money. It gets hot in Phoenix in the summer (duhh!) and the heat that you pay for when you light your bulbs you then have to pay to pump out of your house with the AC. Ok, so maybe it is all about money. In some respects, LED bulbs are a twofer.

Now, there’s a downside. Both CFL and LED bulbs require power at entirely different voltages than incandescent lamps. Every bulb has a little power supply in it, and to keep the power supply circuitry small, the supply uses a technology that generates a lot of RF noise. If the whole house is running LED bulbs, I’m guessing that my IC736 will deliver audio that sounds like the center of a raging thunderstorm, only 24/7. I don’t have my shack wired up yet, but it’ll be interesting to see what happens when I run a temporary longwire out to the pool shed later this year.

Now, it won’t happen this year and perhaps not next year, but the 5-year plan includes a new building in the NW corner of our 5/8 acre lot to house my workshop and radio shack. (I’m using the small garage for now, and although I was clever and got everything in, it’s…cramped.) I’m sure I’ll hear our LED bulb symphony (and perhaps the neighbors’) but if I don’t use LEDs or CFLs in the shack, things may be a lot better.

So…what are the chances of opening up the bulbs, pulling out or bypassing the power supplies, and running them at the LEDs’ native voltage? This isn’t an idea original with me, and in fact one chap has a very nice article up on Instructables. The 40W bulb he dissected delivers 30VDC to its LED array, and he had to do some major surgery to rewire the array to take 12VDC instead. My approach would be to figure out what DC voltage a given type of bulb generates for its LEDs, and then build a high-current passive (i.e., non-switching) power supply to deliver exactly that voltage to all the modded bulbs in the building. (Note that there’s nothing magical or standard about his 30V figure. That’s just what the maufacturer happened to use in that particular model of bulb.) This would require running a separate 30VDC (or whatever) power network inside the workshop building, but since it’s going to be a custom building, I can do that.

We’re not nearly done with the house and landscaping here yet, and I won’t have a great deal of loose time until the summer. (We still have work to do on our Colorado house before we sell it.) I’ll start a research binder on LED bulbs in the meantime, and maybe allow myself a few hours at some point to pull a cheap bulb apart to see what its LEDs are eating. If any of you have played around with LED bulb internals, (or have come across any pertinent links) by all means share in the comments. I have a hunch that a lot of very clever guys are pondering this problem right now, and I’m looking forward to hacking the hardware myself. I haven’t done much building in the last couple of years for various reasons, and damn, I miss it!


  1. Mike Weasner says:

    WARNING! Be certain those LED bulbs are 3000K. Otherwise you will be receiving a lot of harmful blue frequency light. The AMA now acknowledges a lot of human health issues (cancers, Alzheimers, Parkinson’s, and more) from some types artificial light at night, including the bright white LEDs. To learn more visit the International Dark-Sky Association web site ( Of course, living in Phoenix now you will have to suffer through a lot of light pollution. There are some efforts there to reduce the light pollution from Phoenix street lights.

  2. I assume that anything south of 3000K is acceptable? I only use 2700K bulbs in the house, and I doubt I would use anything higher than that. This brings up the question of whether the plastic used in the bulb has anything in it that filters out the blues. Will research that. I’m not sure what sort of test gear it takes to read the spectral signature of a bright light source.

  3. TRX says:

    > running them at the LEDs’ native voltage

    I thought about that too, and since I’m still looking at bare studs inside, it would be easy enough to run the wires. We have some of the highest electric rates in the country, and anything I can do to keep from shoveling money into the local electric company is usually good.

    However… I grew up under incandescents and flourescents. In my shop and current home it’s all flourescent. I don’t see any of the flicker some people claims gives them a headache, and I like the bright white light.

    I made a mistake and bought some “natural” flourescent tubes once, and tossed them out after a few weeks. They look blue to me, and everything looked weird.

    The problem I have with LED lights is ALL of them, so far, look pale blue to me. Which would be great if I was living in a post-apocalyptic zombie movie, but it geshtupfs actually seeing things.

    I’m still planning on running low voltage wiring, but I guess I’ll be waiting for the next generation lighting after LEDs…

  4. Rick says:

    I have started to replace CFLs with LEDs. Even though the CFLs haven’t died yet, I think the energy savings will help a bit. Any CFLs that turn out to be excess will be donated to a local charity of some sort.

    I got a new dining table fixture which used 60-75W bulbs. It’s on almost all day and half the night. Replaced the bulbs with LEDs. I like the light much better (it is a brighter white), even though there is a <1sec delay between 'turn-on-the-switch' and 'lights are on'.

    Got some dimmable LEDs for the TV/den. They provide more light on the dim settings than the incandescent. And a brighter white light than the dull almost-orange of the incandescent when dimmed.

    I will be replacing more of the incandescent and CFLs with LEDs. Quite pleased with the results.

  5. RH in CT says:

    I returned the one package (brand forgotten) of LED bulbs I bought at Costco. The package claimed instant on, the first one I installed was anything but. I made a video of the two lights on the circuit turning on when I threw the switch; the Cree (from Home Depot) was instant, the one from Costco was about a half second behind. That doesn’t sound like much but I found it annoying as all get out.

    Over the kitchen sink we have a fluorescent fixture set into the ceiling. In the winter it gets too cold to start so we kept it on 24×7. The last time the bulbs were going I bought LED replacements that required rewiring the fixture to remove the ballast and put the power to one end. Unfortunately it causes the FM radio mounted under the cabinet next to the sink to buzz awfully. What a PITA!

    When a circular fluorescent tube was dying recently I decided to buy a new fixture and to LED. I went with one that would take three conventional bulbs since I get 40 or 60 watt equivalent CREE LEDs at Home Dept for $4 and I wanted flexibility of putting in just what we needed. Shortly after Michael Covington wrote of replacing a fixture with one that had LEDs built in, something I made a point of avoiding. He made a good point though – because his fixture was not designed around “bulbs” the LED array could be designed to be spread out, a simple approach to heat problems than LED “bulbs”.

  6. Mike Weasner says:

    The International Dark-Sky Association has a spectral analyzer for lighting that connects to an iPhone. I’ll be getting a demo of it next month.

  7. Richard Clark says:

    One other thing when shopping for cheap LED bulbs – check the lifetime. I saw a box somewhere locally for about $1/bulb and got all excited, but then I noticed that the lifetime was only about 2000 hours – about an order of magnitude lower than the more expensive ones.

    Looks like the manufacturers are figuring out the planned obsolescence angle already.

    1. Interesting. One thing that occurred to me is that the lifetime of LED bulbs is (in part) limited by heat, and that the cheap bulbs may cut costs by pumping more current through fewer LEDs, raising the heat dissipated in any single LED.

      This implies that quality bulbs run cool. I can touch the plastic bulbs used in the two 40W 2700K Cree bulbs in my desk lamp, and they’re only mildly warm. Rugged, too: I dropped one on the tile floor here while I was putting them in, and not only didn’t it shatter, but the bulb still works.

      The 60W 2700K Feit bulbs that I was talking about in this entry run hotter, which you’d expect. They also have heat sinks, which the 40W Crees do not. The Feit bulbs also take a small fraction of a second to come up to full brightness, which doesn’t really bother me, as it suggests that there’s some sort of inrush current protection in the LED driver circuitry. So far none of the LED bulbs I’ve used have failed, while the CFLs I tried some years back died in mere months, and in the winter took almost a minute to come up to full brightness.

      Because we replaced all our 60W ICs here with identical LED bulbs at basically the same time, I have a good chance to observe in coming years how many bulbs of this model fail how quickly. It may be years still, but I’ll report on it in this space.

    2. RH in CT says:

      Google led bulb teardown and you will find all sorts of looks inside various bulbs with analysis of where the costs are being cut.

  8. paul says:

    I’m not sure if this is applicable, but have you considered an RV style 12V light fixture? They make LED bulbs for these, and this particular example comes with LEDs installed, type 921 wedge base.

  9. Jack Smith says:

    Lots of luck avoiding switching power supply noise. Some of my experimental loops and voltage probe antennas are 200 ft from the house and the closest one is 150 ft and there’s plenty of noise below 100 KHz. Computer switchers are perhaps the worst offenders.

    Have not disassembled an LED lamp yet, but a couple of CCFL lamps had jumpers installed on the PCB where RFI filtering (LC) parts were supposed to go. Suppose the filter parts were used during emissions testing and then no longer used.

    My radio shack is a mess – recently acquired a Collin S-line and a Collins 51S1 general coverage receiver and until I am physically up to it, they will remain on the floor. Looking forward to putting the S-line on the air.

    For some time now, most (maybe all?) new fluorescent 4 ft lamps use an electronic ballast – yet another noise generator.

  10. jim f says:

    I bought the 65 LED flood replacements from Costco…they work great. I replaced about 24 incandescents. I also have been buying the 4 foot LED replacements for my shop lights…they are about $38…but they work better in the cold and give nicer light and save a little over the fluorescent bulbs. I have bought a number of the 60w bulbs too…they work great…

  11. Tom Roderick says:

    I do think LED’s are the way to go for lighting, but something has to be done about the RFI. A few are not too bad, but when we had over 1,300 installed in a Christmas display around the tower with our repeater receiver antenna it about shut down our repeater for over two months.

    Our technical crew made some measurements and the noise floor of the repeater receiver was between 20 and 30 Db higher from early November through the first week in January when this display was on 24/7.

    This isn’t just about inconvenience since that repeater is an important element for disaster communications in this area.

    I suspect the part 15 standards are only considering individual emitters but light bulbs are not always used that way.

  12. nick flandrey says:

    I replaced the can lights in my kitchen with lamp assemblies from costo, and got the benefit of the LEDs and a sleeker look, and air sealing! (they have a trim ring that seals against the ceiling) They dim and the light looks good with high color rendering index. They are almost TOO bright.

    I replaced my undercabinet lights with strips of LED (from a roll) and hate the result. They are pro quality strips from a major specialty retailer. The light looks GREAT, and my wife was very pleased. Installation was a breeze. The problem is they are EXTREMELY noisy in RF, wiping out my 80, 40 and 20M listening, and everything in between.

    The problem seems to be the strips themselves, as the psu’s are fully encased in metal boxes and grounded. Add on chokes on the feed lines to the strips don’t help at all. Investigation with a portable SW receiver has no increase in noise when I touch the PSU boxes, and huge increase when I touch the strips.

    I have to turn them off to hear anything, which is what I do. Happy wife=happy life, so I won’t be removing them anytime soon, but I might still do a bit of investigation.

    I’d suggest taking a portable SW receiver (you’ve got one somewhere, right?) and listen before adding more…


    1. How clean is the DC to the strips? Have you put a scope on it? If power to the strips is clean, I don’t understand the physics, unless the LEDs are being operated in a mode I’m not familiar with.

      Most of my gear is still in boxes; there’s a great deal to be done vis-a-vis the Big Move, and at 63 I have to ration my energy a little. But this whole business fascinates me. I ran into a tailgate company at a recent hamfest with all sorts of LED products, and I’m looking forward to putting together a ceiling LED fixture driven by a battery on trickle charge–or something. About all I can do is gather data; actual bench work won’t be possible until probably the end of summer.

  13. nick flandrey says:

    I’ll scope it when I get a chance, that’s a good idea. Probably they are not particularly clean. But I suspect it must be the copper traces on the strips (led every inch surface mounted to the tape) acting as antennas for whatever pulse is coming out of the PSUs. I haven’t had a lot of time to look into it, as I can just turn them off when needed.

    I forgot to mention, the LED bulbs can have the same mechanism of early failure as some CFs, bad caps. I’ve opened a couple and they had exploded and leaky caps. So the LED might have 20000 hr life, but the caps fail much sooner.


    (If Pournelle’s law is “It’s almost always the cable.” Someone should have the first law of failed modern electronics, especially power supplies, “It’s almost always bad caps.”)

    1. Amen to that. I bought a pair of tube-era wireless intercoms in 2012, and a cap inside one of them exploded when I plugged it in. See:

      I replaced all the little electrolytics in my Samsung 214T monitor, and may have to do the same to Carol’s old 204T, which stopped working shortly after we moved to Phoenix. Also, back in the 90s I bought a Heath Comanche mobile receiver, and one of the electrolytics exploded when I plugged it in. I’ve since used a Variac to ramp up power to old gear; the intercom didn’t get that treatmnt, but the cap was a tubular mylar and wouldn’t have benefited anyway.

  14. nick flandrey says:

    DC power disto, especially using PoE to power lighting loads, is gaining momentum in the commercial space.

    There are several systems and proposed changes to codes underway.


  15. Dave Malley, K1NYK says:

    FWIW, I have read that LED’s are designed to be run right side up, i.e. screw base on the bottom, so that heat generated by the LED’s rises above them. The article mentioned that LED’s mounted upside-down result in the generated heat flowing over the bulb and limiting life. But I’ve not seen if this is actually considered to be valid physics.

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