3-way LED bulb teardown and why you should consider them

The Cree 3-way LED bulb (L); the Cree 100W-equivalent (M); the Cree 60W-equivalent (R).

The Cree 3-way LED bulb (L); the Cree 100W-equivalent (M); the Cree 60W-equivalent (R).

When Cree came out with their 3-way bulb a couple of weeks ago, I thought, big deal. They already make a 60W- and a 100W-equivalent LED bulb, so a 3-way just sort of smushes them all into the same bulb.

But then I read how Cree said that it was the second most requested LED product, and I remembered my intense dislike of phase-cut dimming switches. Perhaps 3-way lights could be another work around for dimming, as was the dim-on-rapid-switch approach (which so far I haven’t seen take off), whereas 3-ways are apparently already popular with some consumers. Hmmm.

So I got my hands on a Cree 3-way ($22, Home Depot; AFAIK not eligible for rebates) and switched it on, noticing the very obvious visual difference between the three light levels: 320 lm (30W-equivalent); 820 lm (60W-equivalent); and 1620 lm (100W-equivalent). Cree says that in the old incandescent 3-way bulbs, the common 30W/70W/100W was not too useful because, while the human eye can easily see a difference between 30W of incandescent light and 70W, the difference between 70W and 100W is barely discernible. Because of the way the incandescent bulb and the lamp fixtures switch works, incandescent bulbs are constrained to the brightest light being the sum of the two lower lights.

Here’s a brief summary of how the switch works: A 3-way incandescent bulb has two separate filaments, most commonly a 30W and a 70W filaments. The base of the bulb has three different contact points: Ground to the threads (same as a regular bulb) the hot connection down at the center of the base(Also like a regular bulb, and another hot connection, insulated from the first, that’s a ring around the first hot connection at the base of the bulb. (See photo.)

The base of the Cree 3-way bulb. The neutral is the threads; the dot in the center of the bottom is one connection to the line voltage; the ring around it is the second line connection.

The base of the Cree 3-way bulb. The neutral is the threads; the dot in the center of the bottom is one connection to the line voltage; the ring around it is the second line connection.

So the switch position on a 3-way lamp will either power one filament or the other, or both together, or all off. For a 30W/70W/100W bulb the brightness levels are the lowest level, 30W, the brighter filament, 70W, or the sum of both, 100W.

In  the world of incandescent light, you’re stuck with the brightest light being the sum of the two filaments. But how does it work with LEDs? Because LEDs are current-controlled devices, Cree’s bulb works by varying the current through the LEDs in three levels.

Because 3-way bulbs enable dimming without having to use a phase-cut dimming switch — which is a noisy mess — the Cree LED 3-way bulb can do without the circuitry required to smooth and filter the output of a dimming switch.

Cree 3-way bulb LED tower

(Never operate this or any other bulb with its cover off; It has exposed line voltage.)

With the top off, you can see that the bulb’s LEDs and heat sink is the same as the Cree 100W-equivalent LED bulb. Regardless of the switch position, all of the LEDs are illuminated with the same current — there’s no switching in banks of LEDs to mimic the way that the incandescent bulb switches in different filaments. I’m guessing the board uses the same chip family as we saw in the 100W bulb teardown, which is possibly a custom version of the STMicro 656X power controller family. This time the cryptic marking is “E2 4LE”; the 100W-equivalent bulb’s IC read “E2 3zE.”

Close-up of the 8-pin power IC.

Close-up of the 8-pin power IC.

As you would expect from a PWM-driven bulb, the color temperature and CRI stays quite constant regardless of the light output of the LEDs. (Measured with MK350 handheld spectrometer.)

[Table 1]

Switch position Lux CCT CRI Watts Power Factor
30W-equivalent 462 2681K 82 3W 0.9
60W-equivalent 1050 2654K 82 7.9W 0.98
100W-equivalent 2041 2674K 81 18.7W 0.99

The measured power factor is quite high for the bulb, especially at the brighter outputs. If high power factor is important to you, note that 3-way bulbs have an advantage that they can maintain a high power factor at all times, unlike phase-cut dimmers where the power factor goes way down when the bulb is dimmed.

The pc board for the 3-way bulb is quite similar to the 100W-equivalent version, in keeping with Cree’s game plan of standardizing on one basic hardware platform.

Cree LED 3-way bulb pc boards

Both inputs from the base’s switch contacts are fused and then fed into the bridge rectifier.

Both inputs from the base’s switch contacts are fused and then fed into the bridge rectifier.

So I’ve made an about-face, from not being able to see the benefits of a 3-way bulb to becoming a grudging supporter. I personally don’t use dimming on my home lights, but for those who need dimming and don’t want to go the phase-cut dimmer switch route, with all of its noise and poor performance, the 3-way is a good alternative.

Oh, and maybe you thought you don’t have a 3-way lamp fixture in your house? If you have a common table lamp, and have ever wondered why you have to switch the darn thing twice to get it to go on or off, you have a 3-way fixture. The second “click” is the switch looking for the 3-way contact.

I also saw 3-ways from Philips, Osram Sylvania, and TCP being demonstrated at LightFair this month; the market may be heating up.

Comments

  1. Bruce Aleksander says:

    This type of lamp is perfect for one of my vintage lamps. I hadn’t even known that someone was manufacturing this in an LED retrofit. My particular fixture is a Laurel Lamp with one of those beautiful hand-blown frosted glass shades. It completely encloses the lamp, which makes me wonder how well the LED will be able to dissipate heat. when enclosed. There’s the possibility for radiant heat loss, but no ventilation. I’d love to see some future tests along those lines, since we know how heat can affect both the luminous output and lamp life. Thanks for your column! I always learn something from reading your research!

  2. Hi Bruce, the packaging on this light says, “Not for use in enclosed fixtures” which is also what the 100W-equivalent version says. However, the 60W-equiv version does not have this restriction. So if you mostly use it at the 30W/60W settings it might be ok.

  3. Bruce Aleksander says:

    That’s too bad the CREE won’t work in an enclosed fixture for the full range.
    I wonder if the liquid cooled Switch 3-way lamp would work. I’ve heard they
    Can be used in enclosed fixtures.
    http://www.earthled.com/products/switch-switch-3-way-led-light-bulb

  4. Robert Moskowitz says:

    Too bad it is not their TW technology. I got their 60tw bulb and won’t go back. My wife cannot work with lighting with the low R9 rating. ‘Take it out’, she says.

  5. Bruce Aleksander says:

    The CRI of just barely in the low 80s is unfortunate. It’s almost too bad that the eyes will adjust to and accept such a wide range of “white” as normal. It’s not until they have to make critical color decisions under the poorly color-quality lights that they begin to notice the difference. CREE’s “TrueWhite Technology” lamps have CRIs in the 90s, and that’s what I would always want as my baseline for CQI (Color Quality Index).
    Anyone who has tried to sort different shades of navy blue socks under discontinuous spectrum light sources will appreciate that extra 10 points. Perhaps we should include a Sock Sorting Score to the package label? ;-)

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