Cree has entered the LED replacement bulb market with its own name brand bulb. Cree is offering both a 40W and 60W version of the light; My review here covers just the 60W version.
Here are the specs:
- 800 lumens
- Light appearance: 2700K
- Life expectancy: 22.8 years, based on 3 hrs/day
- Warranty: 10 years
- Power: 9.5W; 120Vac, 79mA
- Power Factor (measured): .98
- Sold at Home Depot
- $12.97 ea; or six-pack for $74.82 ($12.47 ea.)
- (The 40W-replacement version costs $9.97 and uses 6W.)
First, the cosmetics: It’s similar in looks to a 60W incandescent bulb. The incandescent weighs 28.3 grams (1 oz) and the Cree weighs 113.4g (4 oz.), so it’s a little heavier, but still quite light.
It dims quite nicely, with absolutely no flicker at the bottom end. I hunted around at the low end of the dimming range, right where the light turns off, but couldn’t make it flicker or flash. I tried dimming with both a Lutron Maestro dimmer and a garden-variety cheap triac dimmer, but the light output was smooth at all times. Very nice.
Along with flicker, audible noise is a bugbear for many LED bulbs. How does the Cree stack up? I had to get my ear within 12 inches to hear any hum at all. Aha, I thought, there must be some serious potting compound inside the bulb to damp out the high-frequency inductor noise. (Spoiler: I was seriously wrong here.)
The color temperature of 2700K — a standard color temperature for LED replacement bulbs –is warm and pleasant. Cree does offer the bulb in a much cooler 5000K temperature and prices it a bit higher, most likely because at the cooler temperatures the bulb is more efficient at producing light. The 5000K bulb requires only 9W to produce 800 lumens compared to the 9.5W of the 2700K tested. In addition, people tend to think of the cooler temperature light as being inherently brighter because of the stark contrast with shadows. However, to live with on a daily basis, stick with the 2700K version.
At this point, I’m through with a consumer review for the Cree bulb. The light is warm and pleasant, the dimming excellent, there is no annoying noise, and it costs less than $13. Go buy one – it’s a great value and supplants my previously favorite LED replacement bulb, the Best Buy Insignia.
But what lies beneath? What design decisions did Cree, one of the Big Three LED component manufacturers, make when it put on its hat as a consumer product manufacturer?
To do a tear down, the first challenge is to remove the silicone-covered glass bulb cover. I used my favorite method (told to me by Peter Di Maso of Texas Instruments) for removing LED bulb covers: Soak it in the oven at 200F for 20 minutes and then twist the cover off while wearing thick leather gloves.
Worked like a charm. Even better, it was still possible to operate the light and probe for some voltages. At full power, the voltage across the LEDs was 220Vdc; When dimmed to where the light cut out it was 207 Vdc. 220V is a pretty high voltage for powering an LED light. What’s up with that? Let’s take a look at the LED array.
As you can see, the LEDs are mounted on a column that sticks up through the center of the light. (These are white LEDs, that is, blue LEDs covered with a white-light-emitting phosphor.) There are a total of 20 LEDs mounted in ten groups of two on a metal core pc board that’s scored between each two LEDs and then bent into a ten-sided shaped that slips over the column.
You can also see that each yellow-colored LED has four bumps in it. These bumps are probably LED emitters, so each individual LED component is actually a tiny matrix of four LED emitters that share the same phosphor coating. So that makes for [CORRECTION] 80 LEDs in series. (For more information about the LED used and how careful selection can reduce the BOM costs, see: How Cree saved on BOM costs in its LED light bulbs.)
There was no isolation transformer, indicating that the design was non-isolated (which continues the trend we saw in the Insignia bulb.) Non-isolated LED drivers drop the parts count significantly and shrink the space needed for power management, dimming, and power factor correction (PFC). As you can see from the photo below of the front and back pc board photos, this bulb has amazingly few components. It also has excellent PFC: I measured .98 PF with a Kill-o-Watt meter.
Sure enough, the 8-pin IC is a STMicroelectronics L6561D transition mode power factor corrector, driving a three terminal 3N40K3 N-channel 400V, 2A power MOSFET, also by ST. Apparently, the PFC pre-regulator operates as the power management for the entire drive circuit.
I was impressed that the circuit was not potted, which is very unusual, especially in such a quiet bulb.
In addition, rather than relying on kludge-y hand-soldered connections, the bulb uses a couple of clips to transfer the power from the center of the LED column to the LED array on the outside of the column. (See the photo of the LEDs on the column above; The clips are on the left and right side of the column.) The whole assembly almost snaps together, making it easily and reliably assembled.
Also of note: It’s
made assembled in the USA.
UPDATE: For more info on Cree’s design decisions read: Q&A with Cree about 60W-replacement LED bulb.