What current is drawn by LED mains night light?

Agreed.

That's how I'd examine the changes in phosphor behavior. Remove it and test.

Jon

[...]

I can (sometimes) comfortably live not knowing, by simply moving on to a technology that doesn't have a certain problem. This sometimes drove my father crazy.

Yes, they are. Sometimes there just isn't enough time to figure all that out.

There's some truth to that. Just got stuffed boards in, extremely dense placement, almost no silk screen possible. Had instructions in there to ask if in doubt about orientation. Well, whaddaya know, a nasty-to-solder chip was flipped. Arrrgh! Just brought it all back to Fedex a couple hours ago.

OTOH what drove me nuts in Europe was the bureaucratic hurdles that people blissfully accept. I don't, and every time I see red tape that gets my blood boiling. So at some point I had to get outta there ;-)

Yeah, the ego thing. Westphalians (where I was born) are said to be, by their own law, always right :-)

I believe the lighting research is done in Aachen though. Nice university town, tons of great pubs.

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All of the inorganic phosphors used in white LEDs degrade from use to some extent or another. The basic chemical formulation that I usually hear of is YAG (yttrium aluminum garnet), doped with I-don't-know-what.

I meant getting involved somehow in a bad photochemical reaction that degrades the phosphor, migrating into it if necessary to do so.

I was talking about both those and the common smaller ones. The smaller ones were producing 6 mW of blue light from 20 mA back around 2000, and many are probably producing 2-3 times that now - from a die whose overall width is .3 by .3 mm.

I think the rate at which the phosphor damage is occurring would be proportional to intensity, along with varying directly and in this case a lot more than proportionately with photon energy. Absorbing a second photon before releasing energy stored from the first may be the problem or a major part of it.

My experience is an unknown-brand 5 mm white LED having phosphor degradation cutting visible light output roughly in half in 4000 hours at

30 mA, along with the remaining light becoming more bluish in color. I have had an older version Cree "X-Lamp" do the same thing but at a slower rate.

Possibly poisoned by other materials adjacent to the phosphor. Maybe YAG with dopants that cause it to fluoresce from photons having 2.6-2.7 eV is not as sturdy as the phosphors you have experience with.

Quench degradation of the phosphor, or quench the functioning of the phosphor?

- Don Klipstein ( snipped-for-privacy@misty.com)

As a fluorescent lamp ages, its electrical characteristics do not change much until either filament is depleted of functional thermionic material to an extent causing the cathode fall to increase significantly. At that point, the lamp's hours are numbered and it is entering "end-of-life".

There are lumen maintenance curves published for some fluorescent lamps, and "initial lumens" and "mean lumens" for a greater number of them. Phosphor degradation is the issue here. The rare earth phosphor mixtures used in "triphosphor" lamps degrade more slowly than halophosphate phosphors do, but they still degrade.

Discoloration from evaporated/sputtered electrode material is usually a very minor issue with most fluorescent lamps until they get into end-of-life conditions. At that point, higher cathode fall leads to the ion bombardment that causes more spectacular sputtering, and one end (sometimes both) significantly blackens over a length of usually about

2, sometimes 3 times the diameter of the bulb.

The usual white LED phosphors are YAG (yttrium aluminum garnet) doped with some cerium compound (maybe oxide?) with the cerium in the +3 valence. I have seen a bit on lutetium and gadolinium being used in addition.

I do know that I had an LED night light that had its light output decrease by about half and become more bluish in color gradually during about 6 months of continuous use. The LEDs were unknown brand 5 mm ones being operated at about 30 mA. Most 5 mm LEDs have dice around .3 mm by .3 mm, with being between 60 and 90% of the total die top area passing outgoing light.

I also know that I had an earlier version Cree "X-lamp" lose some of its output (not nearly half however) and become a little more bluish in color after about 3500-4000 operating hours at full rated current (350 mA) and a heatsink temperature around 75-80 degrees C or so. The LED was being run within its ratings, but I considered the temperature adventurous more than conservative. The die was nominally either a .9 mm square or a 1 mm square.

- Don Klipstein ( snipped-for-privacy@misty.com)

I think you meant near/over 685 lumens per watt for this wavelength range, where scotopic sensitivity in lumens per watt is defined to be the same as photopic at 555 nm which is about where photopic peaks. (I give a chance that the definition of "scotopic lumens" *may* be 1700 per watt at a wavelength at or close to the scotopic peak and *not exactly* 683 at the wavelength around 555 nm where photopic is defined at

683 lumens per watt and close to peak).

Blue LED night lights with low luminous output are appealing to some due to high output in "scotopic lumens". Most of their output is in the range of 450 to 485 nm. Output of one of these lights in photopic terms can be a fraction of a lumen, but to dark-adapted vision easily illuminates a room and can even illuminate adjacent rooms enough for some navigation.

- Don Klipstein ( snipped-for-privacy@misty.com)

My experience is that neon glow lamps mostly do not age on the shelf nearly as much as they do in use.

Where do you get the idea that neon glow lamps have helium?

He-Ne lasers have helium mixed with neon, in proportions with helium being the majority. Helium atoms have generally higher energy levels than neon atoms have. Excited helium atoms excite neon atoms into the upper level of the 632.8 nm transition better than free electrons do.

As for neon glow lamps, there are a few formulations accounting for the vast majority of them:

1. Pure neon, in "high intensity" neon lamps such as C2A (NE-2H) and A1C ("mini NE-2H"). At 120V, these depend on their favorable electrode coatings being in good shape. After a couple to a few 10,000's of operating hours at 120V, these usually start flickering, and also show photoelectric effect - behaving better when there is light hitting them from outside.

The color is a slightly reddish shade of orange.

1. Neon-argon mix, traditionally 99.5% neon .5% argon. This is a "Penning mixture", where the lowest excited state of the majority gas has more energy than the ionization potential of the minority gas. This favors ionization. Neon glow lamps with this one include A1A (NE-2) and A1B ("mini NE-2").

The argon detracts from visible light output due to argon's spectrum being mainly infrared. A little argon does a fair amount of dimming because its energy levels are lower than those of neon.

In a "main discharge column" such as in a sodium vapor lamp having Ne-Ar mix and just started and still cold, the color is between the usual ones of neon and argon, varying with current density to more-neon-like at higher current density (roughly "reddish hot pink", common in just-started sodium lamps using this mixture) to more argon-like at lower current density (magenta to a violetish purple). In the cathode/negative glow in glow lamps, the argon manages to not significantly glow, and also manages to dim the 585.2 nm yellow wavelength of neon less than most of neon's other strong visible wavelengths - resulting in an orange color "less reddish"/"more yellowish" than is the case with pure neon.

1. Neon or neon mixture including radioactive Krypton-85 - less common nowadays than a few decades ago, and these were a bit special a few decades ago. Those had some bit of shelf life issues, since Krypton-85 has a half-life of 9.4 years.

- Don Klipstein ( snipped-for-privacy@misty.com)

I suspect you carbonized the epoxy (or whatever the encapsulant material is), and maybe also cooked the die (chip) or possibly caused electrolytic overvoltage damage to the die.

- Don Klipstein ( snipped-for-privacy@misty.com)

Yes, that's how I imagine I understand it. [I'm somewhat familiar with the emitters used in elecron microscopes, which depend upon both thermionic and field emission effects (Wehnelt cap, for example.)] Which can lead then towards a fairly rapid decline, then.

Yes, usually measured in thousands of hours, though. At least, from my experience. Like I said, I'm still having difficulty here with night lights and a claim that the phosphor simply quit.

Very noticeable.

Although I don't know what LEDs that web site was talking about, that's what I'm curious about. Where the web site talked about using higher quality LEDs, I believe I have to assume that if it is true that the phosphor is the issue then they must use different phosphors. And that's what I'm wondering about. Your above comment would, I presume, suggest some subcategories I might consider for what is used in the better quality ones. Not those which are the subject under discussion.... unless you know what the web site author was discussing.

I assume there is a mixture, by the way. They don't use a single phosphor.. or do they? (Lu containing phosphors, memory serving, tend to emit with peaks nearer the 425nm area. Do they use those? Gd is all over the map, so to speak, ranging from 500nm well into the 700's of nm.)

Of course, I have an easier time imagining that the LEDs just died and that the phosphor is probably quite similar to that used in 'high quality' ones. But I don't know one way or the other.

You are talking 4000-5000 hours, then. And "half output." Quite a different thing, unless I failed to read the web site well. (Possible.)

Well, we are back onto performances that wouldn't shock me nearly as much, then. Oh, well.

Jon

I use some YAGs, quite regularly, with both LED and xenon flash. They just work. Yes, they do degrade. But night light, 3 months, low level LED emissions at 3eV, down to "not working?" Nah.

Disassociation of YAG to the point of a complete failure in 3 months with a blue LED emission? I'm going with some other LED failure without better support.

Yeah. What I thought you may have meant, then. I'm sorry. I'm just not buying 3 months, night light, weak blue LEDs, YAG phosphor, disassociation of the YAG to the point where the fluoresence is essentially gone.... Not yet. I need to see a mechanism.

You are talking 4000 hours and "half output." As I elsewhere said, quite a different thing, unless I failed to read the web site well. (Possible.)

I've used maybe half a dozen YAGs (Ce, Cr, several Eu's, and a few others.) I'm not sure if there are any common ones I've missed using. There's a YAG:Ce that absorbs pretty decent at 2.6-2.7 eV (65% or so) and emits at a peak of about 550nm that might be used. I don't know, but it looks attractive to me from the sense that it absorbs more strongly in the area you describe than any other I'm aware of. But it's pretty rock solid -- made at about 1300C for a total of 4 hours in a lab... or at closer to 1800C and (better) more when done with combustion synthesis. It's kind of sturdy stuff. A lot of the other YAGs don't even absorb well (20% or less) at 2.6-2.7 eV. Anyway, I'm curious.

Well, I was thinking about fluxes and epoxies in a way I haven't experienced before. I suppose we are also possibly talking about heat quenching, but frankly I just have a real hard time going there with night light LEDs. Yeah, with fluxes above 10W/cm^2 I might be all over that. But sheesh! Night lights? And keep in mind that this is an effectively dead night light in 3 months. I'm liking a poor emitter a lot more than I'm liking YAG going that bad that fast.

Anyway, I'd like to learn. So if there is a clear mechanism here and a poor phosphor, I'd like to know about exactly which phosphor and manufacturing process is involved.

Thanks, Jon

I agree here...

In fluorescent lamps - phosphor life varies with basic chemical technology as well as with irradiance. Irradiance varies among the various kinds of fluoreascent lamps, and ones with higher phosphor irradiance have greater need to use "triphosphor" type phosphors as opposed to "halophosphate" type phosphors in order to have "sufficient" "slowness of degradation".

As for the claim of quickly quitting - I see any truth here to being very outright defective implementation of any or any combination of involved technologies.

I have a milder claim - of an LED nightlight having low-power white LEDs with likely some version of usual-YAG-type white LED phosphor, losing about half its light output and its color becoming noticeably more bluish over roughly 4,000 operating hours.

It appears to me that most white LEDs that do not claim color rendering index 80-plus, especially if "neutral white" or "cool white" (color temp.

4,000-plus K), have a simpler phosphor formulation with a single "chromophore".

I am aware of earlier Lumileds ones having two chromophores, with one having a minor very-narrowband emission at 611 nm in the orange-red (which I like to associate with trivalent europium or an yttrium oxide "activated" with trivalent europium), and the other being a "broader band yellowish" one typical of YAG phosphors used in white LEDs.

I am also aware of older color rendering index claims by Nichia of some of their earlier white LEDs achieving CRI of 85, while I am aware of more-modern CRI data for similar white LED spectra only achieving 70's. This is in the area of white LEDs having what appears to me to be the phosphor having a single "chromophore" that is somewhat "broadband-yellowish" with highly significant emission from "mid-green to mid-red" (maybe 530 to 650 nm or so).

I suspect that I am making a milder claim than another that has been presented here.

- Don Klipstein ( snipped-for-privacy@misty.com)

Well, at least we can rest there.

Okay. My use never attempts at a 'white', since all I care about is a being able to emit a decent exciting wavelength and maybe having some kind of separation between that and the center of the emission band. But I have been involved in calibrating RGB LED combos for a D65 white point. And I'm sitting here trying to imagine the idea of developing a realistic sense of 'white' from what amounts to some leaked blue color from the LED itself plus some (broad or narrow) phosphor emission from it. Yeah. Maybe. I don't think it would rate very well, though.

As you can tell, I probably haven't even fired up a phosphor-white LED except in some flashlight. I certainly haven't subjected them to the spectrophotometer (mostly from Ocean Optics) tools I use. I suppose it would be fun, when I get some time.

Yes, there's a nice 611nm commercial phosphor (YOE and P56 acronyms) which is Y2O3:Eu+3, just as you say. I gather it's widely used in fluorescent lamps and in projection TV tubes and maybe even plasma displays. It has a nice emission spike right at 2.03eV (611mm, as you say.) Apparently, from the research papers I see here (1960's), it can be sensitized for excitation at 365nm (3.4 eV) using a little Bi (they suggest Bi2O3), but that will reduce its efficiency at 254nm (4.88 eV.) The absorption is perhaps 25% or so below about 4.4 eV (longer than about 282nm) and reaches about 90% at about 5 eV (248nm.) It's definitely not well excited anywhere near 400nm, though. Nothing better than 25% on the chart I see, here. Probably less.

Thanks. One day, I'm going to see about checking the lines and gathering some spectra and then running that through the software I also wrote to produce the CIE color coordinates from it.

Well, then I suppose I have little to add or subtract.

Jon

High power LED cost around $1 per watt. A 7W LED should be equivalent to a 60W bulb for around $7. It would take around 2 years to recover the cost with energy savings.

LED can sell if subsidized by utilities like CFL currently does.

Only if you don't care about your electric bill.

There is one advantage of LED over CFL. LED lights can be focused to a distance where light is required. For example, we have high ceilings in the house. CFL are bright at the ceiling, but dim on the floor. LED can light up the floor much better than CFL.

[snip]

We also have very high ceilings, 12' to 16'.

Would it be better to use a white LED or make white light with blue, green and red LED's? ...Jim Thompson

-- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at

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he

LED comes in very pure white, better than RGB LEDs. In fact, people like to mix it with yellow white for warmer feel. Of course, if you want occasional special effects of color LED, then RGB would be nice. But most home are wired for on-off only; so, it's hard to control the colors. According to the factory, pure white and yellow white are the most popluar LEDs.

=A0 =A0 ...Jim Thompson

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What is your definition of "pure white" ?

At least the shape of the spectrum for all "white" LEDs I have seen differs significant from the spectrum shape of a block body radiator at any temperature. The CRI (Color Rendering Index) is quite bad.

Paul

How about cost per lumen? Aren't "white" LED's more expensive? ...Jim Thompson

--
| James E.Thompson, P.E.                           |    mens     |
| Analog Innovations, Inc.                         |     et      |
| Analog/Mixed-Signal ASIC\'s and Discrete Systems  |    manus    |
| Phoenix, Arizona  85048    Skype: Contacts Only  |             |
| Voice:(480)460-2350  Fax: Available upon request |  Brass Rat  |
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Coming soon to the elementary school in your neighborhood...

I pledge allegiance to Dear Leader Barack Hussein Obama and to the
community organization for which he stands: one nation under 
ACORN, unchallengeable, with wealth redistribution and climate
change for all.

I guess the correct term is "cool white", similar to light output of fluorescent tubes. "Cool white" is popular in factories. But for homes, people prefer "warm white" (yellowish). In the lobby of a nice hotel, they have alternating "cool" and "warm" LED spot lights. I like that mixture better than either one.

to

n the

Not really. With economy of scale, white LEDs are most cost effective. LED lights are very popular in Asia and Europe. We (US) are a little behind in building or using them.

=A0 =A0 ...Jim Thompson

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=A0 =A0 =A0 |

That's too high. And you can't present examples with long runtimes, the consumers caught on to that ;-)

But in the end you and I pay.

We have _massively_ replaced incandescents with CFL. Usually 40W->7W and

60W-> 13W. I took a look at the average bills, IIRC it was 2005 compared to 2008. No difference to write home about. The reason may be that we both grew up in households where the parents had to go through wars and famine. So we were taught never to leave a lamp burning once it was no longer needed. Now that makes a big difference.

One of these days I'll try it. But first tey have to become cheaper ;-)

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