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Philips' Pricey LED Bulb Has Impressive Specs

Posted April 18, 2012 9:10 AM

From CNET News:

Philips' L Prize LED bulb, which will go on sale Earth Day for $50 online and in stores, brings a big jump in efficiency, life, and light quality. [Read more]

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#1

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/18/2012 4:04 PM

Philips' bulb uses deep-blue LEDs. The yellow 'filter' seen in the photos is designed to fluoresce yellow whilst allowing a bit of blue light to pass through. The eye sees the combination of blue and yellow as white, with the specific colour temperature set by the ratio of these two colours.

I bought some of Philips' bulbs and removed the filters. Here are some photos I took of the bulbs with 'filters' on and off.

I hope the driver in Philips' new L Prize LED bulb is more efficient than the one in these. The metal base on these bulbs gets very hot - too hot to touch -- signifying that the driver electronics are themselves dissipating a lot of power as waste heat. It would be interesting to see how much.

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#2
In reply to #1

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/18/2012 10:35 PM

I hope you protected your eyes from the UV. I don't recommend others try this.

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#3
In reply to #2

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 2:02 AM

These are blue, narrowband LEDs - the same blue, narrowband LEDs which are sold for lighting and signage which requires blue LEDs be used as the blue component of RGB displays. The wavelength is longer than even longwave UV 'blacklights' which are also in common usage and safely so. The UV you are cautioning against is shortwave UV. These wavelengths are not produced by blue LEDs. These LEDs aren't even capable of producing shortwave UV. They're quite safe.

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#5
In reply to #3

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 8:24 AM

Interesting. It's the same physical mechanism that is used in the more common type of white LEDs - a blue LED chip with a glob of yellow phosphor over it; the other common type being RGB White LEDs. The phosphor glows yellow and allows some of the blue to come through, yielding a net white output. In this case, they managed, apparently, to imbed the phosphor in the yellow 'caps'.

--I assume that the caps are solid, and do not have a thin coating on the interior that could be scraped off?

This, by the way, is also similar to the phosphor screens on old black and white TVs. Under a magnifying glass, those screens could be seen as a sea of glowing yellow and blue globs of phosphor.

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#6
In reply to #5

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 12:52 PM

I'm wondering if the fluorescent material - which is mixed in with the plastic (no, you can't scrape it off) - is an organic material, given that the phosphors typically used in dab-it-on-the-die construction are based on the rare-earth yttrium.

China is the world's largest producer (and consumer) of rare-earth elements and seems to be leaning toward limiting exports, OPEC-style. Finding alternatives for these phosphors should be a priority. Given the volume of fluorescent material in Phlips' L Prize bulbs, I wouldn't be the least surprised that they used something else, something that is not rare-earth based.

I've not heard of any commercially-available LEDs yet which use quantum dots to determine the colour. Have you? This property of QDs was discovered a few years ago.

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#4
In reply to #1

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 8:10 AM

"The metal base on these bulbs gets very hot - too hot to touch -- signifying that the driver electronics are themselves dissipating a lot of power as waste heat. "

In fact it signifies that the heat transfer structure (all the way from the hot spot on the chips to the metal base) is very efficient, i. e., there is a very low thermal resistance. The metal base is virtually the only way left for conductive heat transport (to the counterpart in the fixture, which evolved for incandescent lamps). You have to keep the LED chips as cool as possible. The old lamps generate a lot more of heat, but you get rid of most of it as IR or convection around the bulb. But LED lamps deal with temperatures too low to use IR cooling. LEDs will have to drop the Edison base to reach higher efficiencies.

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#7
In reply to #4

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 1:02 PM

These LEDs do generate heat to be sure but, looking at the construction, the heat sink backing these LEDs is not of sufficient bulk to conduct the sheer amount of heat dissipated by the base, which is quite large, all things considered. The base contains a switch-mode power supply which feeds the LEDs with a constant current (at constant voltage, as these bulbs are dimmable). It's not just a resistor/rectifier/capacitor network but a real, honest-to-goodness regulated power supply. It is this which is generating the bulk of the heat.

I have another light source which uses this same style of LED: four LEDs bonded to an alumina substrate. Without heat sinking the substrate gets about as hot as the base of this bulb, but bonding the substrate itself to a comparable heat sink makes it run much cooler, as expected. The LEDs contribute, certainly, but they're not the primary source of heat in Philips' design.

Looking at the photos, you can see that the LED assemblies can be unplugged. As an experiment I unplugged them and powered them separately from the bulb's own supply. The base got warm, as expected, but nearly so hot as when running the bulb unmodified.

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#8

Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 1:45 PM

The current source is an SMPS for sure, it would generate even more heat if it were a linear one. Sometime in the near future we will think of replacing the threaded base. It's a relic of the incandescent time as the whole system is. The first (carbon!) filaments set the voltage standard at around 10^2 volts. So now we use an inverter to step up e. g. solar-generated power at a voltage one order of magnitude lower and drive a chopper to reduce it back so we can drive an LED... maybe it will make sense to have 12 or 24 V (DC) independently wired in our homes someday.

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#9
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Re: Philips' Pricey LED Bulb Has Impressive Specs

04/19/2012 4:20 PM

The Edison base has certainly outlived its usefulness and I expect it will be phased-out eventually after cohabitating with its replacement(s) for awhile. We'll see.

As far as line voltage goes, in the U.S. we're lucky to have to step down from only 120 Vrms. The Brits and Aussies both I believe have 250 Vrms at their outlets. Other countries too. Nice for electric tea kettles, tho; the water comes to a boil almost before you turn it on (I hate waiting for mine)!

Lots of infrastructure that isn't going to change any time soon, or needs to. Lots of things don't require low voltages and LEDs can certainly be placed in series and driven at constant current but at a higher string voltage.

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