A fairly-new LED light bulb went dark the other day and since the housing seemed to be made of some kind of harmless plastic, I decided to dissect the device to see if I could figure out why it had failed (Figure 1).
Previously, we discussed for how long a time an electrolytic capacitor can safely be left idled. Hold that thought.
The bulb held an impressive set of electronic goodies. Aside from 32 LEDs on that circular disk, there was a circuit board that turned out to be a constant-current switch-mode driver.
Figure 1 Dissecting the LED light bulb revealed its electronic components.
The first thing I learned was that these things should be e-cycled when they go bad, even though our local e-cycling service does not include these items. The second thing I learned was that there was/is an aluminum electrolytic capacitor in there. That led (no pun intended) to a new realization.
The late Robert Pease once wrote of his displeasure with compact fluorescent lamps. He did later relent, but his original displeasure led him to buy a hundred 100 watt incandescent light bulbs for future use. Stashed away like that, they were going to last for many years with no problem.
I have some of that stuff too. There are light bulbs in my cellar that date back to my early adulthood and I am now a septuagenarian. I would have no qualms about taking those vintage light bulbs and putting any one of them into table lamp service today.
However, the storage life of an idled LED light bulb such as the one I took apart will be constrained by the storage life of that aluminum electrolytic capacitor. These things can’t just be put on a shelf somewhere and then forgotten about for years and years the way a conventional incandescent light bulb can be safely put away.
If my collection of reserve light bulbs included any LED light bulbs like the one I just dissected, there could be a substantial risk of trouble from electrolytic capacitor degradation. My advice would be to put any new LED light bulbs into service fairly soon after purchase. I would even advocate that LED light bulbs should only be sold with a “use by” date on their packaging.
As to why my particular device went dark, I never did figure that out. Nothing appeared to be burned or charred. Unfortunately, the circuitry itself was only partly discoverable because the PWM chip bore no markings.
I was stymied in trying to play Sherlock Holmes.
John Dunn is an electronics consultant, and a graduate of The Polytechnic Institute of Brooklyn (BSEE) and of New York University (MSEE).