2 years ago I bought a bunch of cheap led strings from China. The leds were and still are brilliantly bright. I've used the strings for a bunch of display elements but 1 of the major ones is a 4.5m high 20m wide XMAS 2011 across my roof. I had noticed when I took the strings down last year that the portions of strings that were exposed to the sun the wire had turned black. The portions that were under gaffer tape were still silver visible through the clear wire. When I put the lights out this year I did a quick power up without unwinding the strings and all looked good. On the 1st when things got powered up I had an XMAS 2C11 with the top left segment of the X and right hand half of the 0 missing. Up on the roof I went on the weekend with soldering iron to do some repairs and that's when I got a real surprise. I expected to find a few strands broken but the wire has appeared to have rusted and by rust I mean real rust (iron oxide). Rubbing the wires with sidecutters didn't produce nice shiny copper to solder to. The wires just kept flaking away and I went through inches of wire before I could get shiny enough wires to solder to. I'm not sure what the wire is isn't the clear sheath but it doesn't appear to contain any copper as I never saw the copper colour while cleaning the wires. I guess what I'm saying after all that longwinded drama is try to avoid clear wires on your lights as whatever the conductor is it breaks down with sunlight. If you do have clear strings and the wire has gone black then you are quite likely to have failures with it and possible dramatic increases in the resistance of the wire causing dimness down the length of the wire.