RFI from Cree LED bulbs?

[Bird]

I think I've replaced 42 light bulbs, some incandescent, some CFL, with LED bulbs in the last couple of weeks at a cost of about $347. Some are from Home Depot (Cree), some from Walmart, and 6 from Amazon, com. I tried LED bulbs in my Liftmaster garage door opener and they didn't work; wouldn't come on at all. But our master bath has a fixture (strip?) over the mirror that has 6 bulbs, 2" clear globes with chandelier bases. I've not been able to find any LEDs locally at any price, and the ones I've found on the Internet are $14.41 to $25 EACH!

I see lots of talk about leaving lights on in this thread, and I've kidded by wife for years, telling her that the light swtiches work both ways, not just ON. She's finally started turning some lights off, but one day a week is her house cleaning day and that day she starts by going through the house turning on every switch there is, THEN she starts dusting, vacuuming, and mopping. And not a light is turned off until she finishes. I've asked her why she doesn't do one room at a time, and she really doesn't have an answer. But I ain't gonna complain because she does a pretty good job.:laughing:

 

[Sodo]

Wise man. Let an expert do it how she wants to do it.

Leaving lights on while the heat's on doesn't waste much electricity, but it costs lifetime of an incandescent bulb. Incandescent bulbs can last 14,000 hours but are limited to 1,000 hour lifetimes because consumers haven't cared enough to demand it. Up and down the ladder 14 times more than necessary is a large cost to business though. The Bulb mfrs who got 14,000 hour bulbs down to 1,000 hours are the same companies pumping out the LED bulbs now, I wonder what they will do to LED lifetimes? Or maybe they just get 25 times the profit upfront.

 

[k0ua]

Or maybe they just get 25 times the profit upfront.

You might be on to something here!

 

[MossRoad]

I think I've replaced 42 light bulbs, some incandescent, some CFL, with LED bulbs in the last couple of weeks at a cost of about $347. Some are from Home Depot (Cree), some from Walmart, and 6 from Amazon, com. I tried LED bulbs in my Liftmaster garage door opener and they didn't work; wouldn't come on at all. But our master bath has a fixture (strip?) over the mirror that has 6 bulbs, 2" clear globes with chandelier bases. I've not been able to find any LEDs locally at any price, and the ones I've found on the Internet are $14.41 to $25 EACH!

I see lots of talk about leaving lights on in this thread, and I've kidded by wife for years, telling her that the light swtiches work both ways, not just ON. She's finally started turning some lights off, but one day a week is her house cleaning day and that day she starts by going through the house turning on every switch there is, THEN she starts dusting, vacuuming, and mopping. And not a light is turned off until she finishes. I've asked her why she doesn't do one room at a time, and she really doesn't have an answer. But I ain't gonna complain because she does a pretty good job.:laughing:

Don't poke the tiger, man! :laughing:

 

[MossRoad]

Wise man. Let an expert do it how she wants to do it.

Leaving lights on while the heat's on doesn't waste much electricity, but it costs lifetime of an incandescent bulb. Incandescent bulbs can last 14,000 hours but are limited to 1,000 hour lifetimes because consumers haven't cared enough to demand it. Up and down the ladder 14 times more than necessary is a large cost to business though. The Bulb mfrs who got 14,000 hour bulbs down to 1,000 hours are the same companies pumping out the LED bulbs now, I wonder what they will do to LED lifetimes? Or maybe they just get 25 times the profit upfront.

I've got some lightbulbs in our 4 bulb kitchen fixture that have been in there for 19 years. They came with the house. 1 has burned out. I'll have to pull one and see if I can see what it is.

 

[Redneck in training]

The lights in our kitchen are on at least 10 hours a day. There are 10 75W R30 of them. When first good LEDs showed up on the market we bought 10 of them for about $50 each about 3 years ago. If my calculation is correct they paid fore themselves about a years ago. We have about 65 R30 fixtures around the house. If the light bulb breaks then it gets replaced with LED. My wife is quite picky about light color and she loves LEDs. Another good characteristic is that the color doesn't change when dimmed. Only intensity does. If the new LEDs cost $16 each now it is no brainer.

 

[California]

re RFI: I had to take one LED out from the hall, where it disrupted reception on the flat-panel tv any time the bulb was switched on. (no dimmer on this circuit). In fact this bulb disrupted the tv reception anywhere I installed it, even at the far end of the house.

I took the LED bulb out to the ranch, where the old picture-tube tv doesn't notice it.

 

[bumperm]

If there's RFI, it will most often be from the LED's driver circuitry, not from the LED itself. Since a LED is basically a diode that's forward biased, there has to be some way to limit current so the diode doesn't overheat (thermal runaway) and die. In the "old" days, a simple current limiting resistor was all that was needed as LEDs were low power and drew maybe .020 to .030 amps (20 to 30 milliamps).

With high power LEDs, drawing several amps, a current limiting resister would have to be physically large to dissipate heat and would waste power. Thus high power LEDs will often use a "LED driver"circuit, built into the housing (or sometimes external when sourcing parts, driver, LED, and heat sink, separately on eBay). Depending on source AC or DC, either an AC to DC driver or a DC to DC driver is used. Sometimes, if source voltage is out of range, a boost or buck boost driver is used (this allows say a 6 volt source to drive a 12 volt LED).

LED drivers use a high frequency DC switching circuit as higher frequencies allow smaller (cheaper) circuit components. DC input is switched to form a square wave and this is then fed through a toroidal transformer to step output voltage up or down as needed, The AC is then rectified to DC and a regulated voltage and current output. Unfortunately, the fast rise and fall time of a square wave is rich in harmonics and tends to radiate RFI. The interference problem can often be mitigated with good circuit design, shielding, or distance.

 

[My Hoe]

Interesting thread...subscribed.

 

[Bird]

If there's RFI, it will most often be from the LED's driver circuitry, not from the LED itself. Since a LED is basically a diode that's forward biased, there has to be some way to limit current so the diode doesn't overheat (thermal runaway) and die. In the "old" days, a simple current limiting resistor was all that was needed as LEDs were low power and drew maybe .020 to .030 amps (20 to 30 milliamps).

With high power LEDs, drawing several amps, a current limiting resister would have to be physically large to dissipate heat and would waste power. Thus high power LEDs will often use a "LED driver"circuit, built into the housing (or sometimes external when sourcing parts, driver, LED, and heat sink, separately on eBay). Depending on source AC or DC, either an AC to DC driver or a DC to DC driver is used. Sometimes, if source voltage is out of range, a boost or buck boost driver is used (this allows say a 6 volt source to drive a 12 volt LED).

LED drivers use a high frequency DC switching circuit as higher frequencies allow smaller (cheaper) circuit components. DC input is switched to form a square wave and this is then fed through a toroidal transformer to step output voltage up or down as needed, The AC is then rectified to DC and a regulated voltage and current output. Unfortunately, the fast rise and fall time of a square wave is rich in harmonics and tends to radiate RFI. The interference problem can often be mitigated with good circuit design, shielding, or distance.

:confused2:Wonder how many of our other members are like me and have almost no idea what you're talking about.:laughing: But it's undoubtedly good information for some.