7W LED bulb spills its guts, lives to light another day
I saw an product announcement a couple of months ago from TESS, a Taiwanese manufacturing company, for a 7W LED bulb that, at 560 lumens (lm), can serve as a replacement for a 40W incandescent bulb which typically produces 500 lm. TESS has received UL approval for the light and can begin selling it in the US. It expects the lights to sell for about $22.
I asked for a sample, and TESS obligingly sent along two versions of the light, one in cool while (5000K) and one in warm white (2700K). (The warm white produces 450 lm.) These bulbs are not direct replacements for 40W incandescent because they are non-dimmable. (More on that later.)
I put the warm white bulb to a very subjective test by using it in a table lamp that formerly used a 40W CFL. Although the LED has a more directional light, cast in a 120° angle, it worked fine in the lamp. It has a very faint hum that you can hear at 18 inches or closer, but I wasn’t too fussed about that. The chief charm of the light is that it’s instant-on: There’s no warm-up period like a CFL. The specified L70 lifetime of the light is 10,000 hours. (The specified lifetime of the CFL is 8,000 and they routinely fail in my hours after about 2 years of service.)
I was quite happy with the warm white LED’s color, so I decided to use the cool white light as the sacrificial lamb to see what’s inside. The plastic dome is glued on to the finned aluminum base that acts as a heat sink for the LEDs. (The product box says the LEDs used are Cree.)
As you can see in this close-up, there are 7 LED packages inside the bulb. In addition, there are two empty pads – hmmm, looks like TESS plans on using the same pc board for a higher-power light by dropping two more LEDs. Also, if you squint you may be able to see that each LED is really a package of multiple LED chips – those are the flyspecs dimly visible in the yellow centers of the LEDs. The gray plastic-y looking pad around the pc board edges is a thermal conductive pad for better thermal transfer to the aluminum heat sink.
The base of the heat sink is hollow and packed with the power control circuit. At the left side, there’s a silver-colored clip-on heat sink on the HB LED driver IC. You can also see more of the gray thermal conductive pad stuck between the toroidal inductor and that heat sink, but here it looks like it’s being used to protect the two components from mechanical vibrations or shock if they rub together. The HB LED driver is an MIP552 from Panasonic, which was released in 2007. Although the TESS light isn’t dimmable, the MIP552 does have dimming capability; However, the dimming feature almost doubles the surrounding passive components needed and they probably wouldn’t fit inside the light’s current form factor. Here’s the description of the MIP551/552 on a distributor’s site, with a link to the pdf of the spec sheet. The switching frequency of the LED driver on the spec sheet is 44 kHz.
As you can imagine, it was painful to rip apart a $20+ LED light. However, it still worked after I took the pictures and reassembled it. On the other hand, scotch-taping or super-gluing the plastic dome on top didn’t seem like such a good idea for use in an easily-accessible table lamp. Eureka! It now has a home in the laundry room where it’s one of three lights, hidden behind a light fixture, and it’s exposed guts aren’t so much of a hazard.
With the light on you can see the difference in light pattern and color compared to the CFLs.
So the happy ending: The lights have a home, which also can serve as a life test. Do I like the LED lights? You bet. If price were no object, I would replace all 40W CFLs in the house in a flash.
[I see that TESS just announced a 9W, 700lm bulb – filling up those empty pads visible in the 7W LED.]
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