# Was hoping someone could answer some questions I have about LED Christmas Lights.



## JLPIcard (Nov 28, 2012)

I purchased several strands of Christmas Lights from ALDI for our tree this year. 8 strands of LED lights, each strand has 50 lights on it and cost me $4.99 each. I had put them on the tree, and then after looking at my work, I had decided to swap out some of the colors to better balance the look. Big mistake....

For some odd reason, some of the sockets were wider than the others and even on the same strand. Not sure why that was, I continued on my swap until I could locate a narrow socket bulb to place in the socket. Did that and the light blinked every so quickly and the half the strand went out. Long story short, after trying to rectify that problem I ended up creating the same problem three times on three strands, seemingly causing half of those three strands to fail.

I had to remove all the strands I had already applied it was maddening trying to fix what I had done with them on the tree. The oddness continued however.

For some reason, in several of the sockets no matter how good the bulb was working before I tried to plug it into an empty socket, it would pop and take out the rest of that half of the strand. I was burning out bulbs faster than it took me to buy the damn things. I checked the fuses in the plug, they were all good. I then tried removing some of the LED's from their sockets (the instructions say that if the base is different than the socket to remove the LED and replace it gently into the correct size socket), I noticed that some of the LED's appeard to have a DIODE welded to one the legs of the LED! I think it's a diode, it had a Cathode stripe on one end. At first glance I thought it was a resister, but there are little resisters installed along the length of the strand at a couple spots to serve the whole strand.

All in all, I ruined 5 of the 8 strands! 

I am at my whit's end and there is no tree shining brightly in the household. The Grandkids will be sad, Grandma is also sad, Grandpa is furious, and Santa, well Santa will NOT be pleased. 

Help for an old phart please?


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## Dave_H (Dec 9, 2012)

I haven't really dissected any strings but have a fair idea how they work.

The maximum number of series LEDs for multi-colour is about 35, or
about 25 for whites. Your 50 strings are two series strings connected in
parallel (albeit physically end-end), therefore two resistors. There should
be a high-PRV diode per series string in there.

For series diodes per lamp, are they only in the red, yellow, orange, green,
but not in the white (or blue) ones? I think they may to equalize the voltage
drop so that mixing/matching in a string with the same limiting resistor, the
overall LED drop variation (and therefore current and brightness) variation is
minimized.

As to why they are blowing...don't know. Possibly something you did shorted
out the limiting resistor and/or diode.

On some strings the resistor/diode appears to be inside a socket shell (in one
case, one size larger than the lamps in the string) sealed at the open end. If it
were removable, and you accidentally plugged in a regular lamp, that could explain
things blowing; but it would be poor design to allow the resistor to be pulled like
that and probably wouldn't meet safety requirements.

I have a LED ornament which I swapped LED colours between strings, and it worked
out, so it can be done. I like this particular one because of its high brightness, and it's
full-wave rectified (versus half-wave rectified for most strings) which reduces flicker.

As an aside, very early LED Christmas light strings often had non-replaceable bulbs.
That would prevent mixing/matching.They were expected to last 50k-100k hours. 
I found that blues were especially susceptable to static electricity damage, which
would render some of them dead, while the other colours lived on (actually one
string of greens had the same problem).

Dave


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## Dave_H (Dec 13, 2012)

Dave_H said:


> The maximum number of series LEDs for multi-colour is about 35, or
> about 25 for whites.



I need to correct myself on this (though nobody else did...). The maximum number
in a series string can be up to 50 multi-colour, or blue or white. I have strings of
both that are 50, and some whites that are split; don't know the exact reason.

Dave


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## EricB (Dec 21, 2012)

If blue and white are different like that, it probably has to do with them being made with the newer GaN technology. White is really a blue doped with phosphor. The newer "pure green" (525nm) is also made with the GaN. While blue and green are freely mixed with the other colors, one is hard pressed to find white mixed in an a multicolor string. The Rockefeller Center tree is an exception, and I always wondered where they got those. I am seeing a lot of blue and white "icicle" strings, though. Early multicolor strings with blue had very few blues, and the greens were still the old yellow-green (565). On those first ForeverBright sets I got 10 years ago (multicolor and white) I had tried to add the spare white to the color string, and it didn't light.

So it probably has something to do with GaN. The higher energy blue probably needs different wattage or something. So sockets being different sizes is probably to prevent swapping, as the sockets probably have different current coming in.


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