I have seen LEDs last years in outdoor setup so looks like this can be done. The leds are protected with what looks like shrink wrap and epoxy inside it

I did test some LEDs for quality of sealing by putting ink on the place where the wires are going into the LED. In some the ink diffused in and could be seen extensively on the surface of the wire, up to the chip. In others it did go very little or not at all

So i think that LEDs can be done to avoid this problem or at least to slow it down so much that they'll outlast the incandescents, so still be better than the incandescent lights

You do get a dual layer heatshrink tube, with a thermoplasic glue layer in it. It is a lot more expensive than the regular type, and is mostly used in marine applications for making waterproof joins in boat cabling, or to make connectors more corrosion resistant. Also used in aircraft and military equipment for the same purpose. Do not think it will be used in a dollar lamp set, the sleeving alone would be around $20 per set. There is a special series of cable connectors from 3M, often used in power cable jointing, where they provide a joint that will survive being immersed in seawater for years.

I have seen LEDs last years in outdoor setup so looks like this can be done. The leds are protected with what looks like shrink wrap and epoxy inside it

I did test some LEDs for quality of sealing by putting ink on the place where the wires are going into the LED. In some the ink diffused in and could be seen extensively on the surface of the wire, up to the chip. In others it did go very little or not at all

So i think that LEDs can be done to avoid this problem or at least to slow it down so much that they'll outlast the incandescents, so still be better than the incandescent lights

If it seeps into only one from 100, it mean it does not work.
To be able to say "LED's can be done to avoid the problem" mean, it may seep into no more then one piece per million, so you may rely on that, because that mean only one faulty string in 1000. And still we talk only about new strings, but what happen after few thermal cycles.
And here the present technology is far behind that - it is impossible to recognize and reject the would be leaking failures on the production line, so for a quality manufacturer there is no other option then to state, then they are not sealed and then the water may seep in....
The same is for the sleeves: Making few 10's really sealed does not mean the full production would remain sealed.

In a city not too far away, the counci installed many (tens thousands ?) LED strings few years ago in dense arrays in some central street. Few years later, some faulty segments can be spotted here and there

If they would be incandesent, they would all be out now just by normal lamps EOL

So yes i do claim that well made LED strings hold up better than incandescent strings

In that perspective yes. But the incandescents are designed to have replaceable bulbs (the failing part), while in the LED ones you can not replace the deteriorating part...

I like to use a combination of energy saving LED and the good ol' vintage incandescent Christmas light strings, that way I get the best of both worlds with energy-savings and the awesome glow vintage incandescent lights. When I buy LED strings, I done research on who makes a more quality string of LED's, and I choose the GE sets. I always go for the wide-angle cylindrical LED's which offer a much brighter and more even spread of light. The dome style LED's are more directional and do not offer the same quality of light. I think GE makes the brightest and better quality LED sets.

I can honestly say that I love the LED's when lighting up the front of my house and I can't wait to get some of my vintage incandescent inside color and GE C-9 strings up too!!!! I have a small house, so the energy usage shouldn't be too bad, using a couple of 25-bulb light sets, run along the top and both sides of the porch.

I will be using all vintage Christmas tree light strings inside of the house along with a couple of strings of LED's for the windows inside and will probably run a candolier with the good ol' C-7 GE glazed bulbs. (They sure get hot though :!!)
/Brad

I have some General Electric "Light Show" LED strings that have AWESOME effects!  They are RGB color changing and look like C9 bulbs.  I still prefer old school C7/C9 clear twinkle bulbs though.

@DieselNut I've seen those GE RGB LightShow LED's, those are awesome (but much too expensive)

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Last year I ran both standard Incandescent Mini's and Cool-White LEDs together (as in putting the sets side-by-side) and had things setup to flash patterns/change 'colors'  with them
No problems with anything except the LED-icicles I had...those were crap, probably half the sets had problems with failures(and thats with only one season's use. Don't know what the issue was since I just dumped them in my pile of "junk" lights (thinking about it, August is getting near done, probably about time to think about looking at those damn things LOL) 

I like the bright colors of the LED lights, but I only like the ones that have a plug-in AC to DC transformer (although they don't seem too common) because they provide the bulbs with DC current so the LEDs last longer and don't seem to have the annoying half cycle flicker. I have seen and tried the sets that just plug in with no transformer, but some of them have an annoying 30 Hz flicker that I don't like. Nothing can compare to the look of incandescents, however!

... but some of them have an annoying 30 Hz flicker ...

I guess the flicker is either 60Hz, when the string is made of from back-to-back pairs (one LED conduct one polarity, second the other one), or 120Hz (when there is bridge rectifier in front of the LED chain)

The 30Hz flicker would need a dedicated flasher circuit...

True. But I was thinking of the individual diode that responds to one polarity and ignores the other, so instead of ON OFF ON OFF for a cycle it would be ON OFF OFF OFF.

Allot of times I can clearly see the 60hz flicker of what are commonly called 'half-wave' LED sets.
The 'full-wave' sets are deff better (and all it takes is adding a diode-bridge..a inexpensive part)...but for making lights it comes down to cheap...cheap...cheap... not quality

A set with a transformer (or diode-bridge+capacitors to smooth out the AC) is useless to me since it can't be flashed

I have flash a few sets useing Flasher LED but with color changing LEDs. It have to be stright up DC powered.

I meant flash the whole set as a unit (for my xmas lights outside, I'm using a old computer to control/flash them)

I do have some of those sets with Flasher LED's mixed in (seems to need to be full-wave to work)
Like you say, the color changing LEDs only work on true DC.

Yeah, I've noticed the flicker with those "half wave" LED christmas lights.
However, I think the colors are much, much more vibrant so I guess it's worth it.
It seems to me that the Philips LED sets from past years had the rusty leads problem, maybe it HAS since been fixed...
I agree though, nothing compares to the look of good ole' C9 sets...those, minis, and C9s all have their unique atmosphere to them! I like them all...