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In a basement bathroom, I installed three LED corn bulbs. They're the type sold on eBay direct from a manufacturer and have rows of LED's arranged in rows like a corn cob. I appreciate being able to buy these discounted energy saving bulbs, but they sometimes fail mysteriously. they're the same style, but from different manufacturers.

The three installed downstairs stopped shining brightly, and now glow only dimly when I turn on the power. After turning off the power, all three glow for a few seconds before fading out. The three outlets work fine for an incandescent bulb, so the outlet doesn't seem to be a problem. The basement switch is standard and not a dimmer dial or slide.

Has anyone else had corn bulbs break as a group like this? I'd like to install new ones, but don't want them to meet the same problem as these three. My guesses:

  • glitchy switch transmitted partial voltage while being switched on too slowly
  • humidity from shower damaged inner circuits? Other LED's survived outdoors for years
  • recent wind storm downed power lines, voltage spike damaged LED's
  • Safe to assume you've tried the bulbs in other outlets? If so, I'm going to guess #3 from your list. – Aloysius Defenestrate Jun 15 '16 at 0:56
  • I take it the LED bulbs glow evenly even though they are dim? – ThreePhaseEel Jun 15 '16 at 1:18
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Direct sale eBay "finds" are not direct from a manufacturer, they're either factory seconds, counterfeits or built-to-be-cheap models. Even when "competing" products are offered by several "makers", they are often the same production hucked by several marketers or under several eBay aliases. In any case, they all "fell off a truck" in Shenzhen.

No reputable maker anywhere makes corncobs.

That's a big problem with awesome new technology: people who buy cheap, have a bad experience, and blame the technology.

Try it again with top shelf suppliers like Cree, GE, Sylvania, Siemens etc. Target frequently has GE LEDs on sale for as little as $3 each.

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Cheap LED bulbs use a capacitor dropper circuit to step down the AC mains voltage to something more suitable for running LEDs -- the dropper capacitor used in them is often not a fully mains-rated type and thus vulnerable to being damaged by surges and spikes -- the resulting damage causes a loss of capacitance and would explain why your LED bulbs only glow dimly.

  • This. With cheap LEDs, the main place they cut costs is in the driver circuit, which converts AC to constant-current DC for the emitters. Capacitors wear out, cheap capacitors wear out faster, google "capacitor plague" for a spectacular example. The best drivers avoid capacitors for that reason. – Harper Jun 15 '16 at 2:05
  • Well...avoid capacitors that are guaranteed to fail early ;) (You can't build a LED driver without some caps -- but the better designs can use capacitors that generally won't fail before the LEDs wear out) – ThreePhaseEel Jun 15 '16 at 2:15
  • Outlasting an LED emitter is a high bar... They talk 20 year life, but I think it's going to be longer. Even the best electrolytic capacitors expire, just ask the classic hi-fi guys about their misadventures with old caps. Other kinds of caps, perhaps less so. – Harper Jun 19 '16 at 21:43
  • @Harper -- yeah -- I wonder if you can build an all-ceramic-cap (save for the X cap in the input filter stage) LED driver these days? – ThreePhaseEel Jun 20 '16 at 0:46
  • sure, capless power supplies are being seriously investigated. They are constant current supplies, so chokes have a role, as they resist changes in current in the same way caps resist changes in voltage. – Harper Jun 20 '16 at 0:50

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