Home Depot's $20 EcoSmart LED light: What's inside?
Margery Conner - August 12, 2010
Several weeks ago Home Depot introduced its new EcoSmart dimmable LED replacement light for a 40W incandescent for $20 with a 5-yr guarantee. The light works great – nice, warm-ish, diffuse light, dims perfectly, no noise.
What’s inside? Let’s see…
The light has a hard plastic dome-shaped outer shell. Here’s our first glimpse of the LEDs used:
Not the usual intense light sources we’ve seen in other LED lights: These are large surface-area LEDs that make for a very pleasant diffuse light source. And the light only requires two of them to put out 429 lumens at 8.6W.
Here’s a close-up of the LEDs - I removed one to look for a manufacturer’s label or mark, since Lighting Science Group, the bulb’s designer, doesn’t want to divulge its suppliers.
Compare it to the non-dimmable 7.5W bulb I took apart in February, with its 7 LEDs that put out (according to the specs on the packaging) 560lm.
Well, I couldn’t find a manufacturer’s label, but there is an apparent part number; AM6L1, and the part looks like an LED array, meaning that, rather than a single emitter, the LED packages up several tiny LED chips in one package and cover them with a single phosphor. It’s a good choice to use such a diffused light source – no pixilation.
But whose LEDs does the light use? Here’s a link to the Citizen’s LED catalog. (Citizen is a Japanese LED manufacturer.) It looks like AM6L1 deconstructs to this 6W LED array, meaning that the Ecosmart light derates its two LEDs and runs them at well under 6W each, which is a smart move.
Moving on – let’s look at the drive circuitry. Whoa – the electronics are all encapsulated! This is a good design choice for Lighting Science, since it cushions the electronics from all of the vibrations inherent in a small, easily accessed light bulb, but it’s not so nice for us, as we peer into the guts. No matter – the encapsulation material came off fairly easily, exposing all of the drive electronics.
Now the big question is – who’s LED driver/dimming IC does the light use??
The most promising IC – ie, the one with the most leads — is a 10-pin MSOP with a cryptic “SULB” on the top. (U1 at the top of the board in the photo below.) A brisk Google search reveals “SULB” as the “Top Mark” for National’s LM3445 triac-dimmable LED driver. (PDF of app sheet with SULB.) I could see only one electrolytic capacitor: a 50uF Nichicon rated at 105°C. (The black capacitor-like components are inductors.)
The e-cap (just partially visible to the right) is potential weak link and this design uses a good-quality part. Compared to other LED lights, this one has relatively little hand-soldering. As we know from Geoff Potter’s research, solder joints are the Achilles’ heel of LED lighting reliability. Going with a highly-integrated LED driver part like the LM3445 in itself gets rid of a lot of solder joints.
Now let’s go back to the heat sink. The metal baseplate of the LEDs mount directly on the finned metal heatsink using a dab of thermal grease.
(Referring to the previous 7-LED light example, the LEDs sat on a metal-core substrate and then on a flexible thermal interface before mounting on the heat sink.) Ecosmart uses a simple approach that gets the heat out of the LEDs as quickly as possible.
Its overall design philosophy seems to be to increase reliability by reducing the parts count and thus the associated solder points.
For more on the importance of solder joints as a likely culprit for LED light reliability issues, here’s an article that interviews Geof Potter, LED reliability expert with TI.
Better yet, attend EDN’s “Designing with LEDs” Workshop in Chicago this September 29th and hear Geof speak in person. More information and register here.