A number of months again, I got here throughout an LED-based desk lamp queued as much as exit to the trash. Once I requested my spouse about it, she mentioned (or at the least my recollection is that she mentioned) that it had gone dim, so she’d changed it with one other one. However the system didn’t embrace any type of “dimmer” performance, and I wasn’t (on the time, at the least) conscious that LED lighting’s inherent depth may fade over time, solely that it will inevitably flat-out fail in some unspecified time in the future.
My curiosity sufficiently piqued, particularly since I’d intercepted it on the best way to the landfill anyway, I made a decision to take it aside first. It’s Hampton Bay’s 15.5 in. Black Indoor LED Desk Lamp, initially offered by Residence Depot and at present “out of inventory” each in-store and on-line; I assume it’s not obtainable for buy. Listed below are some inventory photographs of what it appears like, to begin:
See: no dimmer. Only a easy on/off toggle:
I don’t bear in mind once we purchased it or what we paid for it; it had beforehand resided on my spouse’s stitching desk. The Web Archive has 4 “snapshots” of the web page, starting from the top of June 2020, when it was apparently on sale for $14.71 versus the $29.97 MSRP (I hope we snagged it then!), by means of early December of final yr. My spouse took up stitching in the course of the COVID-19 lockdown, so a 2020-era acquisition sounds about proper.
Right here’s what it appears like in “motion” (in case you can name it that) in my furnace room, striving (and successfully failing) to distinguish its “augmentation” of the baseline overhead lighting:
Flip off the room mild, and the lamp’s standalone luminary capabilities nonetheless aren’t spectacular:
And right here’s a close-up of the sunshine supply in “motion”, in case you can name it that, in my workplace:
Scan by means of the evaluations on the product web page and, until I neglected one thing, you gained’t discover anybody complaining that it’s not brilliant sufficient. A number of of the optimistic evaluations go as far as to particularly notice that it’s very brilliant. And mockingly, one of many (few) destructive ones signifies that it’s too brilliant. The specs declare that it has a 3W output (no specific lumens score, nevertheless, removed from a shade temperature), which roughly interprets to a 30W incandescent equal.
Time to dive in. Let’s start with the underside, the place a label is connected to a felt “foot”:
A Google search on “Arcadia AL40165” reveals nothing significant results-wise apart from the Residence Depot product web page. “Intertek 4000145” isn’t any extra useful. And, no matter once we truly purchased it, this specific unit was apparently manufactured in December 2016.
Peeling again the felt “foot”, I used to be initially confused by the three closed-end crimp connectors revealed beneath:
till I peeled it away the remainder of the best way and…oh yeah, the on/off change:
Word the wiring colours. Sometimes, in my expertise, the “+” DC feed corresponds to the white wire, with the “-“ return section dealt with by the black wire, and the “+” portion of the circuit is what’s switched. This implementation appears reverse of that conference. Maintain that thought.
Now for the sunshine supply. With the lamp switched off, you may see what seems to be a central LED surrounded by a number of others in circumference. Conceptually, this matches the association I’ve seen earlier than with LED mild bulbs, so my preliminary working principle was that no matter circuitry was driving the LEDs within the perimeter had failed, leaving solely the central one nonetheless operational. Why there could be such a two-stage association in any respect wasn’t apparent, though I postulated that this similar {hardware} may discover use in one other lamp with a three-position (brilliant/dim/off) toggle change.
Eradicating the diffuser:
sadly dashed that principle; there was solely a single LED within the middle:
Right here’s what it appears like illuminated, this time absent the diffuser:
A short apart at this level: what’s with the second “proper?” within the title? Effectively, after I talked about to my spouse the opposite day that I’d accomplished the teardown however hadn’t definitively discovered why the lamp had dimmed over time, she now mentioned that to the most effective of her recollection, it had all the time been dim. Hmmm. If certainly I’d beforehand misunderstood her (and naturally, my default stance is to all the time assume my spouse is correct…proper?), then what we’ve got is a defective LED from the get-go. However only for grins, let’s fake my dimmer-over-time recollection is appropriate and proceed.
One different root trigger risk is that the facility provide feeding the LED is within the technique of failing, thereby outputting under-spec voltage and/or present. Revisiting the sooner white-vs-black wire dialogue, after I initially probed the solder connections with my multimeter utilizing commonplace polarity conventions, I received a destructive voltage studying:
The LED theoretically may have been working in reverse-bias breakdown (albeit presumably not for lengthy). However extra possible, along side the earlier-mentioned change location within the circuit, the wire colours had been simply reversed. Yep, that’s extra prefer it:
Word that their connections to the LED may nonetheless be reversed, nevertheless. Or maybe the lamp’s energy provide was present output-compromised. To check each of those suppositions, I probe-connected and fueled the LED with my inexpensive-and-passable energy provide as an alternative:
With the connections utilizing commonplace white vs. black conventions, I received…nothing. Reversed, the LED mild output weakly matched that delivered when pushed by the lamp’s personal energy provide. And my standalone energy provide additionally knowledgeable me that the lamp pulls 180 mA at 10 V.
About that “lamp’s personal energy provide”, by the best way (as-usual accompanied by a 0.75″/19.1 mm diameter U.S. penny for measurement comparability functions):
The label refers to it as an “LED Driver,” however I’m guessing that it’s only a regular “wall wart”, absent a plug on the output finish. And a Google search of “JG-LED1-5UPPL” (that’s the quantity 5, not an S, by the best way) additional bolsters that speculation (“Intertek 4002637” conversely wasn’t useful in any respect, apart from suggesting that this energy provide unit (PSU) was initially supposed for a distinct lamp mannequin). However I’m nonetheless baffled by the “DC5-10V MAX” notation within the labeled output specs…???
And eradicating two extra screws, right here’s what the plate the LED is mounted to appears like when separated from the “heatsink” behind it (notice the trivial dab of thermal paste between them):
All leaving me with the identical query I had at the beginning: what brought about the LED-based desk lamp’s mild output to dim, both over time or from the very starting (relying on which partner’s story you’re going with)? The almost certainly remaining wrongdoer, I’m postulating, is the phosphor layer above the LED. I’ve already famous the scant-at-best heat-transfer interface between the LED and the steel plate behind it. Extra usually, as this system undoubtedly exemplifies, my analysis means that cheap designs skimp on the variety of LEDs to maintain the BOM price down, compensating by overdriving the one(s) that stay. The ensuing thermal stress prematurely breaks down the phosphor, leading to shade temperature shifts and lowered mild output, together with eventual full element failure.
That’s my take; what’s yours? Let me know your ideas within the feedback!
—Brian Dipert is the Editor-in-Chief of the Edge AI and Imaginative and prescient Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the corporate’s on-line e-newsletter.
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