The LED-based BR40: A bulb begging for placement that’s drafty

When I did my first teardown of a LED-based light bulb nearly eight years ago, I figured it’d be a one-and-done. In coming to that premature conclusion, however, I didn’t consider the added functionality (such as network connectivity) enabled by the reduced power draw of the LED illumination subsystem versus that of the incandescent precursor. And I also didn’t take into account the diversity of functions (dimmable, three-way, etc.) and legacy form factors that LED upstarts would need to support. Here’s the to-date teardown list, which doesn’t even count LED illumination sources that aren’t bulb-shaped, like touch-activated and motion-sensing panels:

Conventional
Zigbee-controlled
Wi-Fi-augmented
Bluetooth-enhanced
Multicolor
Three-way
Battery-backed, and
Filament-based

Today’s teardown “victim” falls into the “legacy form factor” category. About three years ago, I decided to swap out around a dozen and a half (so far) of the nearly three dozen total mix of BR30 and BR40 incandescent bulbs that were already installed and in use in ceiling “cans” throughout the house when we bought it. The bulbs I’ve to date converted to all-BR40 LED successors had two common characteristics:

They were easy to reach using only a conventional ladder (which, you’ll soon see, has been handy for not only initial but also ongoing access purposes), and
They were in locales, such as the kitchen and my office, that saw frequent use, therefore particularly benefitting from LED conversion from a power consumption standpoint.

Speaking of which, here’s one of the “daylight” (5000K color temperature) replacements installed in my office, both off:

and dimly illuminated:

While I can’t definitively say that I’ve noticed a tangible drop in our residence utility bill post-swap, I certainly now feel better about turning (and keeping) the lights on than I did before. That said, the transition hasn’t been perfect. To my earlier “dimly illuminated” comment, all the multi-bulb circuits I’ve converted so far are “fed” by dimmer switches, thereby necessitating dimmer-compatible LED lights. Specifically, I’d bought a couple of these Sunco bulb 10-packs:

to leave me with some spares inventory, which I’d hoped I wouldn’t need to tap into for a while. Check out this conceptual cutaway of what mine supposedly look like inside:

Granted, mine are 17W/100W equivalents, not the 7W/50W equivalent one shown here. Regardless…hold that thought

Are they “zero flickering”? Not exactly. The bulk of the time I try to use them? Yes, actually. But…well, let me start by requoting a portion of my December 2023 teardown (this time with grammatical corrections made by yours truly to the original source):

Most dimmers installed today are designed to be used with high-power circuits to drive traditional filament lamps which were all quite uniform and dimmable by just a voltage change. LED lamps, on the other hand, are low-power and more complex. An LED bulb is a solid-state product that has built in circuitry (called a driver) that takes high-voltage AC input current and converts it to low-voltage DC current to drive the LEDs. Furthermore, driver specifications are not uniform across the LED industry.

There are many different types of dimmers installed in homes and offices, of various specifications (e.g., resistive; leading-edge and trailing-edge and electronic). So, when using new LED lamps with existing dimmers, matching old technology with new can be challenging.

The drivers in dimmable LED lamps may work with many types of dimmers but not all. For instance, LED lamps tend to work better with trailing-edge dimmers rather than leading-edge dimmers. An existing dimmer may also have a minimum load that is too high for an LED lamp. For example, a 60 W filament lamp may use a dimmer that has a minimum load of 25 W, but the replacement LED has a power rating of 6.5 W – below the level required by the dimmer. Dedicated LED dimmers conversely have a very low minimum power rating.

The dimming experience can also be different with LED. Overall, the LED dimming performance is regulated by the capability of the LED driver/chip and the compatibility of the dimming circuit. Since there are a huge number of possible combinations of lamps and dimmers, it is very difficult to produce an LED lamp that works in all dimming environments.

LEDs currently have a lower dimming range than a filament lamp – LEDs currently dim down to about 10% of the total light output whereas filaments may go down to 1-2%. Low-voltage transformers as used with MR16 12V spotlights also add to the complexity.

Some of the issues that may occur when a dimmer is incompatible with an LED lamp are:

Flickering – Lamps will flicker (can also occur if a non-dimmable lamp is used).
Drop-out – No light output at the end of the scale.
Dead travel – When the dimmer is adjusted, there is no matching change in light output (light may not dim to acceptable level).
Not smooth – The light output may not go from dim to bright [editor note: and/or vice versa] linearly.
Multiple lamps – issues may become apparent when multiple lamps are added.
Damage or failure – LED driver, circuit or LED is damaged or fails.
Load below minimum – The power load of the LED lamp is below the minimum required by the dimmer.
Mixed models – Different models of LED will likely have different drivers, since drivers behave differently this could result in dimming issues.

I’ve personally experienced variants of several of these imperfections so far:

One/multiple/all the bulbs in a given circuit will turn on only dimly, and flicker-filled, even at a supposed “full power” dimmer switch position.
One-to-multiple of the bulbs won’t turn on at all, even with the others fully illuminated.
Dimming the circuit causes one-to-multiple of the bulbs to either turn completely off or to stubbornly remain fully illuminated.
etc.

The “fix” in all these cases? Turn them all off and back on again.

And regarding my earlier “spares inventory, which I’d hoped I wouldn’t need to tap into for a while” comment…again, reality hasn’t matched the hype. I’m reminded of the comment left by reader “vandamme0” to that previous December 2023 teardown:

Today I learned…that you can make outrageous lifetime claims based on single diode reliability at optimum temperature, and nobody calls you out on it because nobody keeps receipts for 18 years, 50,000 hours, or whatever you claim.

So far over the past three years, I “think” I’ve had three BR40 LED bulbs fail (which, if you’ve already done the math, you realize compelled me to buy more spares). Keeping in mind that “electronics things that break make great teardown candidates”, I held onto them, one of which is showcased here. That failure rate may not seem bad in the grand scheme of things, until you realize that:

They represent ~20% of the population of LED bulbs that I initially installed, and
None of the remaining BR30 and BR40 incandescent bulbs, all of which again were already installed and in operation when we arrived here a decade ago, have failed.

When I say “failed”, I should clarify. They “sorta” failed. After I’d turn on a bank of lights for a while, one of the bulbs would spontaneously turn off completely. Turning the bank of lights off and back on again wouldn’t immediately resuscitate it. But if I waited a while, the bulb would come back on…again, only for a while. I noticed that if I unscrewed it and removed it from the “can” it’d resurrect more quickly. Regardless, as time went on, the offender would fail more rapidly and take longer to revive; eventually, I’d just give up, grab the ladder, and swap it out.

The most likely potential failure mechanism, I suspect (and you may have already discerned), is heat. Incandescent bulbs get quite warm in ventilation-deficient “cans”, mind you, but the only thing they’re “cooking” is their filaments. With LED bulbs, on the other hand, there’s not only the LEDs themselves to consider but also all the circuitry in the base. And in a ceiling “can” there’s one other factor to consider; the bulb is pointing downward, which means that (as with similarly oriented CFL bulbs I’ve used and disassembled in the past) the heat rising off the LED array ends up baking the circuitry in the base above it. Lest you wonder, by the way, if I’m using my bulbs in an inadvisable configuration, this “stock” Sunco photo should set your mind at ease:

Enough setup; let’s dive into the dissection. I’ll as-usual start with some overview shots, accompanied by a 0.75″ (19.1 mm) diameter U.S. penny for size comparison purposes:

Some closeups of the markings around the side:

And finally, the tip of the base, both coin-accompanied and standalone:

Last time, the globe (I belatedly realized, to my dismay) was:

Glass
Sealed, and
Gas-filled

This time, conversely, it was plastic and definitely not sealed:

Providing a convenient pathway to the interior:

Mission accomplished:

Rim variance around the circumference:

And now what you’re all really here to see:

Removing those two screws in the earlier photos didn’t get me very far:

so, I redirected my attention to the base:

That’s more like it:

Here’s another closeup of the front of the PCB “plate”, this time unencumbered by its prior surroundings, revealing the ring of “daylight” colored LEDs, a smattering of other circuitry (the IC at left marked BP5178F is the LED constant current driver, while the one at bottom right labeled TB120S is the bridge rectifier, both from unknown manufacturers), and the pass-through connection for the two wires on the other side:

But what’s that other two-lead pass-through connector for? Let’s flip the plate over:

It’s…umm…an electrolytic capacitor:

At this point, with no lack of intentional snark, I’ll reinsert the conceptual cutaway from earlier:

Giggle snort

We’re almost done; let’s get that metal “dish” (acting primarily as a heatsink, methinks…note the thermal paste residue) under the “plate” off to see if there’s anything underneath of note:

And the answer is…nope. That’s all, folks!

As always, your thoughts are welcome in the comments!

—Brian Dipert is the Editor-in-Chief of the Edge AI and Vision Alliance, and a Senior Analyst at BDTI and Editor-in-Chief of InsideDSP, the company’s online newsletter.

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The LED-based BR40: A bulb begging for placement that’s drafty

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