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Resuming course

Sunday 11 January 2015

So it’s been a while. I’d cite a busy work schedule, or fascinating personal life that so totally engrossed me that posting was impossible, but…nah.

So anyway…

I’m going to rant about LED Xmas lights. I have no problem with LEDs in general (full disclosure: I have a tiny amount of stock in Cree, a leading LED device maker) or even the general concept of LEDs for Xmas lights.

Xmas lights are A Big Deal in Ashland. People leave up strands of (usually) white lights and illuminate them all year. It’s A Thing that adds a beautiful element to Ashland’s residential neighborhoods.

I put up three strands of LED bulbs a couple of years ago to replace some incandescents that finally failed after a decade of service. I was thinking: LEDs should last forever (ask my TI watch from 1976); LEDs use less energy per lumen.

But.

Come this season, all three strands had failures: long sections of each strand had bulbs that were out or unusually dim.

LED light strings and incandescent Xmas lights share some common failure points: the bulbs can loosen in the socket, an excess of moisture at the connector can cause a short, the wiring harness can fail at a connectors (plugs and sockets). So LED strings don’t have an advantage there.

Incandescent bulbs since Edison’s original require a pretty strong vacuum to work at all. No vacuum, the filament burns out instantly. This makes a broken bulb easy to spot on the assembly line. It also makes a bulb unlikely to test as working on the line, and then fail due to a bad seal on the filament leads after being installed outside. It’s what’s called “mechanically stable”.

LEDs can come from the manufacturer encased in resin so that the silicon die itself (the “filament”) is never exposed to the air. But the contacts and other electronics in the bulb may not be so well protected; they rely on the plastic bulb to keep out moisture.

So there’s the problem: on the testing line, where it’s relatively warm and dry, before the product is shipped, either kind of bulb is going to pass the final plug-and-glow test. Every incandescent bulb has to have a good vacuum, and that will also keep it from failing when exposed to moisture (like outside, in the rain or snow). But an LED bulb can pass even if it has no protection against moisture getting in and eventually ruining the bulb. So when you put them outside, the same bulb that has to protect the filament in the incandescent light is of necessity a lot more likely to be better at keeping out moisture than the plastic bulb of an LED light.

Testing LED bulbs to the same rigor that an incandescent bulb has to have by design is hard. You’d have to expose the bulbs to heat, cold, and wet for hours at a time, and no vendor is going to do that (very expensive gear). And the warranty is short enough that the return rate during the warranty must be low, so there’s no pressure on the manufacturers to make a product that will really last for years under harsh outdoor conditions.

So I’m still a big fan of LED lights–inside, where it’s warm and dry. Outside, I’m staying with incandescent.

Stay dry.

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One Comment leave one →
  1. Sunday 11 January 2015 10:07 PM

    yah! good to have your voice back in my in box.

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