Teardown of a Greenlite 8W LED light bulb
(Last modified 15 Jul 2012)


On a recent trip to a local hardware store, I saw a stack of Greenlite 120 VAC LED lightbulbs, marked at $6 for a box of two bulbs.  The package clained the bulbs provide 450 lumens, which was advertised as the equivalent of 40W bulbs; plus, the bulbs are dimmable.  Naturally I had to pick up a few.  Naturally, I also had to tear some apart.

Before I start with the teardown, I should mention that these bulbs are brighter than I expected and work well with a dimmer.  I replaced some 60W frosted incandescents with these LED bulbs, in my office ceiling light fixture.  The LED bulbs' light is as bright (subjective, I know) as the original bulbs and I like the 3000K temperature better.  Since they are LEDs, they produce far less heat than the original incandescents, which helps in the summer.



First, the warnings!

This teardown involves breaking the bulb's glass and working with exposed broken glass.  Wear eye protection and work carefully.  The bulbs contain some totally excellent LEDs, but they aren't worth making mistakes or taking shortcuts and injuring yourself.  The instructions below worked for me, but you are on your own for this teardown!


I started by using a pair of slip-joint pliers to crush the bulb's base.  This took considerable hand strength; get some help if you need it.  Another option might be to clamp the screw base into a bench vise and crush it with the vise.  My goal here is to crack the screw base enough to free it from the plastic frame it is mounted on.  Note that I only applied enough strength to crack the seal between the metal wrap (the part with the screw threads) and the plastic frame above it.

With the screw base cracked free of the plastic frame, I used a spare pair of wire cutters to slice away the plastic frame so I could remove the screw base.  There is a small section of PCB that sits inside the screw base and has two small wires connected to the metal parts of the screw base, one to the tip of the base and one to the metal wrap.  I simply tore these two connections off when I removed the screw base.


LED bulb with screw base removed

Another view inside the bulb

Here is the bulb with its screw base removed.  You can see the narrow end of the PCB with some power resistors on it.

Next, I put the bulb in a heavy plastic freezer bag, then tapped the glass bulb with a hammer to shatter the glass.  I was careful to use the least amount of pressure needed, since the LED array is just underneath the glass and I didn't want to damage that.

Glass removed (mostly) showing the LEDs

Here you can see the top surface of the LED array.  There are 18 very large LEDs mounted onto a PCB underneath the white plastic shield you see here.

I used a thin blade screwdriver and a hobby knife to remove the glass shards.  The glass is embedded in a silicone rubber compound that seals the white plastic shield to the glass and to the bulb's metal frame.  I worked carefully on this phase to avoid injury while removing the glass.

With the glass and sealing compound removed, I removed the three screws you see above.  This freed the white plastic shield, exposing the LEDs and the PCB they are mounted on.

The LEDs!

Here is a closeup of the LEDs on their white PCB.  Note that the PCB floats on a thin film of silver thermal compound, held in place only by the tension of the red and black power wires you see in the center of the PCB.  You can see some of the leftover sealing compound on the outer rim of the metal platform below the PCB; this metal platform acts as the LEDs' heatsink.

Details of the LED PCB

Here you see the LED PCB after some handling, as I was tracing out the circuitry.  The dark grey smudges are some of the heatsink compound that I spread while handling the PCB.

Note that the black wire is soldered to a pad marked with a plus-sign and the red wire is soldered to a pad with a minus-sign (between two zero-ohm resistors).  I verified with a DVM that the markings on the PCB are correct; the pad marked with a plus-sign is connected to the anode of the first LED in each string.

The LEDs are wired as two nine-LED strings; one string is LED1 through LED9 and the other string is LED10 through LED18.


Summary
So I now have a small PCB, about 1.5" across, with 8 watts worth of very bright LEDs to play with.  It will be simple to repackage the PCB as a spotlight, garden light, or as a giant pixel in a really big sign or art project.  It would also be easy to harvest the individual LEDs for use in smaller projects.  Total cost for two PCBs and 36 LEDs, six dollars and a bit of work on my part.  By the way, there are some pretty nice parts on the driver PCB that are also worth harvesting.



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