Viribright LED bulb - looking inside

Anders Hoveland

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https://www.youtube.com/watch?v=lHD657EGoCY


The insides of a Viribright 8W LED bulb, note the heat sink. It is not a piece of thin aluminum, it is solid/heavy like the heat sinks used in car electronic fan speed controllers. Between the upper heat sink and the lower heat sink there are solid metal nipples like features acting as heat pipes.

blog96b12686c6c65fe996010994412e3ef8.jpg


Pealing away one of the phosphor rubber caps you can see the LEDs which are clearly not warm white. Philips developed a remote phosphor sheet that converts the blue light into white. This is normally done right on the surface of the LED, but putting distance between the phosphor covering and the LED offers several advantages, such as better color consistency, avoiding color shift caused by the phosphor layer heating up, and slightly higher efficiency as well.

blogd03ad332732e03cad480a28cf6eae62d.jpg


The plastic cover is solvent welded (glued) on all along the rim. It takes time squeezing the cap to break most of the weld, and a few small flat screwdrivers to wedge the clips open. Once inside, there is a screw in the middle holding the 2 heavy heat sinks together. Each LED board has a single screw holding it to the top heat sink. Screws are well tightened and sufficient heat sink compound used. If you take the top heat sink off you can get to 3 more screws to remove the lower heat sink, but I did not go that far. It would require desoldering the 2 wires that go down to the power supply.

(note: these pictures were not taken by me)

What is so interesting about this LED bulb is it does not just use blue LEDs. The interior of the bulb contains 6 sections, and within each of these sections there is a U-shaped row of 12 emitters- 9 of them blue and 3 of them red LEDs. Apparently the red emitters are to help give the light better color rendering and provide higher efficiency, so it is similar to the Philips L-prize bulb in this respect.
 
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From the video- are those 3 dies in each LED? I don't suppose you can measure the Vf across the string- I'm guessing the dies are in parallel which (would) theoretically increase failure rates.

Is there any heat pipe copper around the back of the arrays? I've always hoped someone would build one with little channels in there to help wick heat into the base.
 

JoakimFlorence

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Philips developed a remote phosphor sheet that converts the blue light into white. This is normally done right on the surface of the LED, but putting distance between the phosphor covering and the LED offers several advantages, such as better color consistency, avoiding color shift caused by the phosphor layer heating up,
The YAG:Ce phosphor being used in white LEDs is actually nothing new. In 1975, Sylvania USA released the "Warmtone" mercury vapor lamp, which utilized a combination of Vanadate and YAG:Ce phosphor. Under normal circumstances this phosphor would have given off yellowish-green light, but at the high operating temperatures in the bulb enclosure the emission peak was shifted to longer orange wavelengths. One noticeable characteristic of the bulb (when off) was that the YAG:Ce phosphor gave the frosted white bulb a slight yellow color. In 1983 Philips went on to use YAG:Ce phosphor in its HPL-Comfort lamps. Fluorescent mercury vapor lamps have long since become a thing of the past; or maybe not, depending on how you want to look at it, with the recent (but ultimately short-lived) insurgence of compact fluorescent technology. A few years ago I even saw some fluorescent streetlamps at a traffic intersection. The light source was very compact, I could scarcely believe it (I'm assuming the vapor pressure inside the tubing was not as low as ordinary fluorescent tubes). I even looked at the streetlamps through a diffraction grating, just to be sure they were not actually metal halide.


What is so interesting about this LED bulb is it does not just use blue LEDs. The interior of the bulb contains 6 sections, and within each of these sections there is a U-shaped row of 12 emitters- 9 of them blue and 3 of them red LEDs. Apparently the red emitters are to help give the light better color rendering and provide higher efficiency, so it is similar to the Philips L-prize bulb in this respect.
That's very interesting. So this LED bulb is using 2 different wavelength emitters. I wonder if a third wavelength could be incorporated in there also, to add to the spectrum. I'm not sure which wavelength it would be, or what added benefit it might accrue to the light quality.
 
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JoakimFlorence

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Inside an Ikea Ledare bulb (note that Ikea's regular Ledare bulbs do not have a separate red emitter inside)

ledare-led-ljuskalla-e__0137804_PE296578_S4.JPG





In the bottom middle picture, light emanates from the chip as it is supplied at 1mA, under normal operation the current would be at 400-500mA
The COB module is made by a company called Tridonic.

The light from this bulb is 2700K, >85 CRI
color rendering and quality of the light is noticeably better than other LED bulbs
efficiency is not particularly high, 50 lumens per watt, but I'm sure there is an efficiency/complexity/price tradeoff
 

JoakimFlorence

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These particular Ledare Bulbs (with the separate red emitters) were measured at 88 CRI. And (according to an online review I read) the CRI from this Viribright bulb did not seem all that better than ordinary LED bulbs.
Much higher CRI values are certainly possible from red emitter enhancement, but in these two cases I suspect the exact red wavelength values and ratios may not have been the most optimally chosen for the design specifications (I think they were on to the right idea though). So the results here weren't that fantastic, but that doesn't mean the basic strategy isn't a good one.

Both Viribright and Ikea were later able to achieve better CRI and increased efficiencies using an all-phosphor approach (ordinary higher CRI white LED) and this also simplifies the design and holds down costs. But theoretically, supplementing with a red emitter does have the potential to result in the best efficiency at higher CRI values (we can see that the Philips L Prize had higher efficiency by a substantial margin over any other LED bulb at the time, or Cree's CR22 troffer design). It's all a cost-efficiency trade-off. When your LED emitters and power supply are not best quality to begin with, it really doesn't matter so much if you're using a red supplementation approach, the efficiency still won't be all that astounding. So in this case it looks like the company's design team decided it would be more cost effective to focus their money on the fundamentals—a better LED emitter, with better efficiencies and a better phosphor formulation, than worry about trying to combine two different wavelength emitters and the increase in complexity of the electronics that entails.

And it is much more about efficiency than CRI. When we're talking about 90 to 92 CRI or so, it's not that big of a sacrifice in efficiency compared to an ordinary 80-85 CRI white LED, not with the newer phosphors they are using.
 
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Do you have any closeups of the emitters? It appears to be 3,4, or 5 small (20ma) style in parallel within each diode. If thats the case, not a good choice for what I wanted. However if they're luxeon style large dies then they'd be grand for overdriving.

Thank you.



https://www.youtube.com/watch?v=lHD657EGoCY


The insides of a Viribright 8W LED bulb, note the heat sink. It is not a piece of thin aluminum, it is solid/heavy like the heat sinks used in car electronic fan speed controllers. Between the upper heat sink and the lower heat sink there are solid metal nipples like features acting as heat pipes.

blog96b12686c6c65fe996010994412e3ef8.jpg


Pealing away one of the phosphor rubber caps you can see the LEDs which are clearly not warm white. Philips developed a remote phosphor sheet that converts the blue light into white. This is normally done right on the surface of the LED, but putting distance between the phosphor covering and the LED offers several advantages, such as better color consistency, avoiding color shift caused by the phosphor layer heating up, and slightly higher efficiency as well.

blogd03ad332732e03cad480a28cf6eae62d.jpg


The plastic cover is solvent welded (glued) on all along the rim. It takes time squeezing the cap to break most of the weld, and a few small flat screwdrivers to wedge the clips open. Once inside, there is a screw in the middle holding the 2 heavy heat sinks together. Each LED board has a single screw holding it to the top heat sink. Screws are well tightened and sufficient heat sink compound used. If you take the top heat sink off you can get to 3 more screws to remove the lower heat sink, but I did not go that far. It would require desoldering the 2 wires that go down to the power supply.

(note: these pictures were not taken by me)

What is so interesting about this LED bulb is it does not just use blue LEDs. The interior of the bulb contains 6 sections, and within each of these sections there is a U-shaped row of 12 emitters- 9 of them blue and 3 of them red LEDs. Apparently the red emitters are to help give the light better color rendering and provide higher efficiency, so it is similar to the Philips L-prize bulb in this respect.
 
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