3M is not the first company you might think of when it comes to LED replacement bulbs – they have a background in neither LEDs nor light bulbs. However, there’s more to an LED light than LEDs, and 3M has a significant presence in plastics and films. The company has used this expertise to gain a toe-hold in the lens part of the bulb – its embossed plastic bulb serves as a light pipe within the $25 dimmable LED 60W replacement bulb you can buy at Walmart.
Before tearing the bulb down, let’s take a moment to just look at it, because it’s not your ordinary bulb. (Is there such a thing as an ordinary LED bulb? The Philips bulbs with their yellow secondary phosphors are hardly run-of-the-mill. But I digress.) The first thing I noticed is that this is heavy: I measured 228.9 gms, or a half a pound.
For reference: An incandescent bulb weighs about 34 gm; A 60W CFL is 59.8gm; The Philips L-Prize bulb is 170.5 gms. I only started to weigh the bulbs with the advent of the 3M one, so I don’t have the weight of the Best Buy Insignia bulb, which is an indication that its weight wasn’t so noticeable that I thought I’d better weight these things.
How does it perform?
The bulb emits 800 lumens at 4000K, which is a colder white than most current LEDs. (I see from 3M’s website that it’s also available in a warmer white, but I didn’t see any information for this on the Walmart site.) A couple of years ago when you first started to see the sno-cone type bulbs from the Taiwanese manufacturers they tended to be above 3000K because LEDs are more efficacious at higher color temperatures. Most people prefer the warmer light we associate with incandescent lights (and firelight). So this is a colder light than what most people are used to.
The bulb consumes only 13.5W, which is pretty standard for a 60W LED replacement bulb.
As you can see in the video below, there is flickering during the dimming of the bulb. When I passed through a power level that induced flickering I returned to that level and the flickering continued. However, with power full-on, there was no flicker.
There was virtually no noise – I had to put my ear right up next to the bulb, and even then heard anything only when the bulb was dimmed to its flicker “sweet spot”. Noise isn’t a concern with this bulb.
What’s inside that bulb?
The plastic bulb has eight vertical slits evenly spaced over its top half. Here’s a close-up photo with the bulb full on.
Because it fills the digital camera sensor, the sensor compensates and shows the relative light source over the surface of the bulb. The light comes out unevenly, with the brightest part being the lower half, and at the very top. (The naked eye doesn’t perceive this unevenness.)
Delving into the bulb itself by popping off the top half of the bulb, we first come to a giant metal heat radiator. It sits right next to the slits in the top of the bulb, which let the heat from the radiator out into the ambient air. This also give us a chance to see that the plastic bulb is not opaque white, but instead is a clear textured plastic.
Now is a good time to pull up the video on the 3M website showing the cutaway of the bulb itself:
You can watch the video animation at the end of this post. The picture above shows how the light leaves the LEDs and enters into the light guide. The video also shows how all of the parts nest together.
The nine LEDs are embedded around the base of the bulb, and their light is directed up and out through the plastic, which is actually a light guide.
So now it’s clear why the close up of the light leaving the bulb showed the majority of the light exiting at the bottom of the base. (Although, just to repeat, the top of the bulb is still plenty bright.)
Back to the teardown: The video has revealed all of the packaging of the pc board, LEDs and power components, but we still have yet to see how the power control and dimming circuitry is done. So, here’s a close-up of the power control IC: It’s another TI chip, but this time instead of the LM3445 we found in the recent Best Buy Insignia bulb tear down, it’s the chips little brother, the LM3444. (The “SZTB” mark shows up in a search for a LM3444 data sheet.)
This made me scratch my head – why not, since the bulb is dimmable, use the LM3445, since that part includes all the dimming circuitry in it? Rather than try and guess, I posed my question to 3M Engineering, and right away received an answer:
“…Our earliest efforts did involve the LM3445 to enable TRIAC dimmability. The circuit design was such that a sufficient current was consumed to exceed the holding current of most TRIACs. This means a few milliamps that results in a power waste and then it was still not guaranteed that any TRIAC dimmer would result in satisfactory performance. As a result, the circuit conversion efficiency was inferior.
There are many circuit requirements that can be ranked in terms of desirability, TRIAC dimmability and efficiency are just two of those. Both LM3444 and LM3445 can be configured to enable TRIAC dimmability so the LM3445 should not necessarily be considered the dimmable version of the LM3444. However, with the LM3444 we established a superior conversion efficiency.There are other advantages of our present LM3444 design so that that converter became preferred for our present product.
[We] would like to point out that there are many commercial dimmers available that do not use TRIACs and that perform well with our present LM3444 circuit. If consumers desire dimmability, there is that option.”
I realized from 3M Engineering’s reply that I have been using “TRIAC” to include all ac-line dimmer switches, but this isn’t correct – TRIAC refers to leading-edge dimmers, while trailing-edge dimmers are sometimes (not often) referred to transistor dimmers. (The link goes to a PDF on the Department of Energy site.)
I see from the 3M page on dimmer compatibility that it lists a dozen dimmers that the bulb is compatible with, one of which is a Leviton and the rest of which are Lutrons. I haven’t verified this yet, but it’s likely these are all trailing-edge dimmers.
3M opted to go their own route for dimming and one of the prime considerations was to save on holding current. My experience, as mentioned above, was that there was significant flicker with a TRIAC dimmer. On the other hand, the bulb was virtually noise-free.
The light pipe-based design played to 3M’s strengths in the plastics field. I think this is an indication of what 3M hoped to accomplish with this bulb, which, as a Walmart product, will see very wide distribution: By getting this design out in front of a large audience, 3M has immediately gained credibility for its light pipe design and light architecture, making it much easier to sell to more specialized and higher profit margin applications. From 3M’s point of view this compensates for the relative heaviness of the product and any dimming limitations.