Walmart made news recently with its announcement of a sub-$10 Great Value house-branded 60W-equivalent dimmable LED replacement bulb. As the nation's leading retailer whose name is synonymous with low prices, Walmart is one of the first places consumers look for household products like lightbulbs. So how does its new lamp perform, and what design decisions were made?
The bulb was reportedly designed and manufactured by Chinese lamp vendor TCP. It comes in two levels of brightness: an 800-lm 60W equivalent and a 470-lm 40W equivalent, with each bulb available as either dimmable or non-dimmable. The 800-lm dimmable costs $9.88; the non-dimmable version is $8.88. This review looks at just the 60W-equivalent 800-lm versions, and primarily the dimmable.
Fig. 1 is a side-by-side front view of the dimmable and non-dimmable versions of the bulb.
Can you see the difference? Me neither. The only marking on the packaging is on the lower corner of package's side panel. The only marking on the bulb itself is on the non-dimmable version. (See left arrow in Fig. 3.)
The dimmable bulb has no marking indicating its dimmablility. This can make for confusion both at the point of sale and once the bulb is at home and separated from its packaging.
Fig. 2 is another example of the bulb's confusing packaging: The package is marked, "Rated for indoor/outdoor enclosed light fixtures," while, as you can see in Fig. 3, the bulb itself says, "NOT for use in totally enclosed luminaires." So which is it?
The bulb's performance specifications say it produces 800 lm at 11W. The small print on the bulb's base says it consumes 10.5W, and my Kill A Watt meter says it consumes 9.3W and has a power factor of 0.93. The "soft white" version is specified at 2700K, which seems pleasant and bright.
How is the dimming performance? An initial quick run up and down the brightness level with a wall-mounted dimmer switch seemed to go okay. However, a subsequent test, with considerable time spent "hunting" for dimming anomalies, turned up some problems. The bulb periodically flashed at certain brightness levels and also flickered. You can see the flickering in this video: http://youtu.be/fZyzI05ghZ8.
(For a more detailed explanation of my dimming test, read the article here: "Walmart's sub-$10 LED bulb flickers and flashes".)
This is not good: Flashing and flickering are not acceptable in any lightbulb. I might be willing to cut the bulb some slack because there are a lot of dimmer switches out there…except that Walmart doesn't provide a list of dimmers that they have verified it works with.
What about the light pattern? The bulb is a sno-cone design, meaning that the LEDs sit on a flat plate and project their light out like a spotlight or flashlight beam. This means that the bulb is not omnidirectional, like an incandescent light or even like a CFL. Fig. 4 shows a crude approximation of how the light is distributed: The dark patch at the bottom should be almost completely lit. (Read this post for more on how the ring works.)
(Note that spotlight beam patterns do have useful applications — for example, a can fixture in a tracklight.)
A sno-cone design inherently has trouble producing light that goes down towards its base. The Energy Star definition of omnidirectional light is light that is evenly produced over 270° (±135). A look under the Walmart bulb's sturdy plastic cover in Fig. 5 shows why this light pattern is so difficult to achieve with a sno-cone design.
This cover did not budge and required cutting to get it off. This difficulty in getting the cover off is a good thing in general, because, like most other LED bulbs I've recently torn apart, the bulb has a non-isolated LED driver design, meaning that the AC grid power is exposed when the cover is off. So, Walmart, nice job on the sturdy bulb cover attachment.
The cover is plastic; the external base below the cover is aluminum.
With the cover off, we can see the LEDs themselves and how the structure of a sno-cone design prevents omnidirectional light. Thirty-eight LED components in plastic packages sit on a metal-core pc board, which is in turn mounted on a round metal plate. The importance of this metal plate is that it transfers the heat from the LEDs' pc board out to the round metal collar at the base of the bulb that radiates heat out to the ambient air. Note that this metal base has no heat fins as is common in other LED bulbs such as the Cree and the Philips L-Prize bulbs.
Yes, the metal base gets hot: I measured 150°F with a IR gun thermometer. 150°F is similar to what I measured on the Cree bulb, but there's a crucial difference in bulb design: The Walmart LEDs are in plastic packages, while the Cree and Philips LEDs are in ceramic packages. LEDs in ceramic packages are much more resistant to thermal aging than those in plastic. Cree's use of ceramic-packaged LEDs is probably one of the reasons it's able to offer a 10-year warranty on its bulbs; Walmart only offers a 3-year warranty.
Because the LEDs are mounted horizontally on the metal plate, the LEDs' light path is limited in projecting their light downward toward the base of the bulb. Some light ends up going down, but mostly after striking the bulb cover — which acts as a diffuser. This plastic bulb cover does a nice job of not allowing the LEDs to appear as hot spots, which does happen with the Cree bulb, but it's a consequence of the high diffusion of the bulb cover.
Fig. 6 is a close-up of the LED array, showing the connection from the driver electronics that sit below the LEDs in the base of the bulb.
Two wires carry the DC power through a hole in the mounting plate, up through a matching hole on the LED array's metal-core board. The wires are hand-soldered to the top of the metal-core board and secured with a large blob of glue. This hand-soldering of the power wires to the LED array is typical of China-manufactured LEDs. Contrast this with the clips that allow the Cree electronics to snap into place. The Cree bulbs are assembled in the US, where the relatively high cost of labor makes hand-soldering something to be avoided. However, because hand-soldering is statistically one of the biggest failure points for LED lights, the use of clips is probably another one of the reasons Cree can offer its 10-year warranty vs. the Walmart bulb's 3-year.
Fig. 7. Shows a first look at the drive electronics:
One of the bulb's key components is the IC that handles all of the power control algorithms. Because it's the largest IC with the greatest number of pins, I suspect that the IC pictured in Fig. 8 is the power conversion IC.
Note that the chip has 10 pins at one end, a large space with no pins, and then 2 pins at the opposite end. This gap in the pins probably serves to isolate the high-voltage section of the IC's internal circuits from the low voltage.
The chip also seems to have had its identifying marks etched off. I have heard via the comments on the original article that the part is the SSL21082T control IC from NXP. NXP would not comment on the device. (Please keep in mind that problems with dimming are most often in the implementation of a design, not in the design of the control IC itself. I have seen several control ICs that dimmed fine in one bulb, yet were also used in another bulb that had dimming problems.)
It's difficult to imagine, with its lack of an omnidirectional light pattern and poor dimming performance, how this bulb can get an Energy Star qualification. Why is Energy Star so important? Because the majority of utilities in the US require an Energy Star qualification to grant a rebate to a buyer of an energy-efficient bulb. (The bar is even higher in California, where the CEC requires bulbs meet 'California Quality', including a high CRI, to qualify for a utility rebate.) Cree's 60W-replacement bulb, which was recently awarded Energy Star certification, would seem to have the upper hand in gaining consumer confidence.