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Photo of only one light illuminated

I noticed that in various strings of lights only one was illuminated. It seems implausible that all but one out of several hundred blew. What caused this and why did this particular light turn on?

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closed as primarily opinion-based by laptop2d, brhans, Elliot Alderson, pipe, W5VO Apr 23 at 10:11

Many good questions generate some degree of opinion based on expert experience, but answers to this question will tend to be almost entirely based on opinions, rather than facts, references, or specific expertise. If this question can be reworded to fit the rules in the help center, please edit the question.

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    \$\begingroup\$ I think there is too less information to answer this question without speculation, and there is probably neither no way to validate an answer in order to accept it. \$\endgroup\$ – Huisman Apr 22 at 21:33
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    \$\begingroup\$ Never seen serial streetlights on cables from street-corners before. But if there enough mutual coupling to power 1 bulb out of say 30 in series. The bulb with the fastest warm-up time draws all the induced voltage ( e.g. 240/30) due to 10:1 PTC effects \$\endgroup\$ – Sunnyskyguy EE75 Apr 22 at 22:14
  • \$\begingroup\$ Looks a lovely park not far from the Welsh coast \$\endgroup\$ – Sunnyskyguy EE75 Apr 22 at 22:21
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    \$\begingroup\$ How about this: The lamps are on a photocell-switched circuit, but one lamp is lit constantly to indicate that the circuit is powered. It's not dark enough to trigger to photocell switch. \$\endgroup\$ – Hot Licks Apr 23 at 1:23
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    \$\begingroup\$ Holiday lights have the so called "shunt wire". The shunt is a small wire wrapped beneath the filament that allows current to continue flowing through the circuit by creating a path of lower resistance than the original path in case the filament opens. For details -> energy.gov/articles/how-do-holiday-lights-work \$\endgroup\$ – Gianluca Ghettini Apr 23 at 14:50
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enter image description here

Figure 1. The intriguing light bulb has caught the attention of Smokey the Bear too.

There can only be a few possibilities:

  • The lamps are spread across several phases or split phases, the other phases are off and all but this lamp has blown. This is very unlikely.
  • Some joker has installed a battery powered lamp. This too seems unlikely.

"When you have eliminated the impossible, whatever remains, however improbable, must be the truth." Sherlock Holmes.

  • The impossible has happened and all have blown but one. This could happen with an overvoltage - by lightning, for example. Some combination of poor contact, tough filament, arcing in another lamp (which would limit the voltage), etc., may be enough to let it survive.

Another possibility is that the power is on and that each bulb has its own light sensor (like some streetlights) and this one is the first to switch on. Again, unlikely.

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  • \$\begingroup\$ I'd go with the battery powered hypothesis, there are available lamps that include a battery back-up \$\endgroup\$ – Jasen Apr 22 at 21:24
  • \$\begingroup\$ Are these lamps connected in series or parallel? Or several series strings in parallel? \$\endgroup\$ – Toor Apr 22 at 21:24
  • \$\begingroup\$ looks like parallel festoon fittings to me \$\endgroup\$ – Jasen Apr 22 at 21:25
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    \$\begingroup\$ Then the o/v has my vote. Someone may have fitted a single 275V (very likely 260V) globe as a spare. We had these in Western Australia for a long time and they lasted forever back when we were 250V and the rest of the country 240V. (almost always higher in both cases). \$\endgroup\$ – mckenzm Apr 23 at 0:54
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    \$\begingroup\$ What about if someone replaced one of the bulbs with an LED lamp? They can sometimes light up on a much lower voltage. \$\endgroup\$ – Thomas Padron-McCarthy Apr 23 at 9:03
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I'd go with the implausible explanation. All the bulbs are blown except the one.

Most festoon lights use a screw-in socket so all the lights are in parallel:

enter image description here

It's certainly unlikely in the extreme that the lights are in any way series connected.

I'd suggest that the string was perhaps hit by a truck (or a surge) and a bunch of the lights broke.

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