LED Xmas lights

Thanks for the correction. :)

TVs CRT has phorphors that is too slow to make it barely objectable.

When time permits I'm taking down two old fluorescents down was magnetic ballast & old housings and put up new one with electronic ballasts and proper housings that reflects lights towards floor. These items are already bought and waiting to put up.

Cheers, Wizard

Have you actually seen LED xmas lights with this in person? They have a

"Joseph Meehan" wrote in news:cC5gf.219357$ snipped-for-privacy@tornado.ohiordc.rr.com:

The X-mas lights wire insulation probably gets degraded by UV exposure,or damaged by weathering. Maybe dirt and moisture gets into sockets,corrosion creates resistance and new,undesirable current paths.

It prolly wouldn't take a very big electrolytic capacitor to level those current pulses out, huh?

Easy to do fer your own strings I guess, but that doesn't help for all the others you have to look at.

Fortunately that 60 Hz flicker rate is above what triggers photosensitive epilepsy in most persons sensitive to that.

Don't even need a capacitor, a simple bridge rectifier changes it to

My thinking wuz that by using just a cap, you wouldn't change the total energy delivered to the string of LEDs significantly, but with full wave rectification you'd double it and possibly blow an LED if the original design had them powered pretty close to their safe limit. Capice?

Jeff

For an example of overdone xmas decorations, see:

Good thought! But you have to put a diode somewhere to protect the electrolytic capacitor from seeing AC. I guess you could "sacrifice" the

That shows another this Jew doesn't know about Xmas, I've never examined a string of LED lights to determine just how they work.

I'd assumed there was a half wave rectifier and maybe a series resistor there already there, to avoid exceeding the LED's PIV ratings.

But maybe they avoid that with a parallel diode across each LED and a single series resistor for the whole string, that's similar to what I found inside one of our white LED nightlights when it started acting funny because the LED was having a nervous breakdown. (It stayed dark even though plugged in, but flickered on when I switched an inductive load on the same circuit - a bathroom vent fan.) Soldering in a new LED fixed that sucker.

Anyway, you got my point, full wave rectification would most likely double the power dissipated in the LEDs if everything else in the circuit stayed the same.

Jeff

Adding a single diode and capacitor will also increase the current because the capacitor will bring the DC voltage up to the peak value of the AC line, usually considered to be 177 volts. As I had a string of

All sounds reasonable, maybe some more LEDs in the string and a cap large enough to remain charged close to peak voltage would be an economical way to avoid *any* flicker.

I think we've about "saucered and blowed"* this one by now, but I am curious about how those series strings handle the reverse voltage across the LEDs. Do they have diodes or resistors across each one or do they just depend upon the summed inverse breakdown voltages keeping the reverse current from ever getting large enough to blow an LED? I'm guessing maybe that's it, do ya happen to know the answer?

Jeff

• An old "down Maine" expression referring to method of cooling a too hot cup of coffee by pouring some into the saucer and blowing across it, returning it to the cup when it's ready to drink.

They depend on the latter, don't think for an instant that these things are over-engineered, or even well engineered.

Really though, in practice I've found LED's to be far more tolerant of reverse voltage than the specs would indicate.

Check out the Philips brand ones at Target.

They resemble the Forever Bright ones of the past 2-3 years. The manufacturer mentioned on the package sounds familiart to me. However, LEDs get improved gradually over the years, and I suspect they also had to get brighter to get Philips to put their name on them.

At Target, they show some in operation - see if they're bright enough for you. I saw some with bare LEDs - those had somewhat narrow beams and were weak outside their beams, while ones with "bulbs" over the LEDs shone more equally in all directions.

- Don Klipstein ( snipped-for-privacy@misty.com)

Make sure the LEDs don't overheat from getting twice as much average current! But if nothing goes wrong, they will not only not flicker but they will also be brighter.

Keep in mind that if they are going to overheat, they may not do so quickly. One thing that can happen is "thermal runaway" - where higher temperature makes the LEDs more conductive, and this situation reinforces itself. This may wait until a moment when the line voltage or the ambient temperature is higher. Keep in mind that such a modification voids UL certification and increases your liability should a fire start - even if a flaw in the product was a contributing factor to the fire.

- Don Klipstein ( snipped-for-privacy@misty.com)

I sometimes see flicker in TVs and monitors set to 60 Hz. I usually see flicker in monitors set to 56 Hz.

I also only sometimes see LED lights flickering when they have 60 Hz flicker. I suspect that the flicker gets more visible when the light source is more intense - possibly explaining why LEDs are more likely to visibly flicker at 60 Hz than TVs and monitors are.

Movies have a high duty cycle and a much shorter offtime than halfwave rectified LEDs.

- Don Klipstein ( snipped-for-privacy@misty.com)

I really wanted to buy some LED last year, they were real cheap at an after Xmas sale at a Nursery. The white ones, (the only ones I was interested in) were too "cool" for my taste. I love the yellowy glow of regular incandescent "white" lights, seems homey, warm & inviting. The LED's looked harsh & "office-light" like for my tastes so I took a pass.

FWIW... they must be popular, as from what I could see Target or mass marketers, from what I could see, sold out before Christmas

I hope they soon come out with a warmer version, for I can't wait to be done with cheap incandescent xmas lights buring out and driving me absolutely crazy. .

I'm going to say one word, and you decide if you still like your theory.

Persistence.

I wonder if instead of using a bridge, just put a big ol' capacitor on the LED side of the string. That could smooth out the peaks and not add any energy.

If not, plugging the string into a lamp dimmer would cut down the energy, if the LEDs are getting too bright (and hot).

Yesterday I tried experimentally running one of the Forever Bright strings off a bridge rectifier, no capactitor. It seemed only slightly brighter. That's puzzling because although instantaneous brightness would stay the same having twice as many flashes per unit time ought to seem something like twice as bright.

Also, I noted an alleged 10V drop across the bridge (121V in, 111V out) but I think this may be a figment of my DMM's imagination, perhaps unable to give an accurate RMS reading of the pulsating full wave rectified DC. I guess I should dig out my analog VOM. And maybe visually compare a couple of C9's incandescent bulbs (considerably more current draw than an LED string) on either side of the rectifier.