LEDs as lamp replacements

Eeyore wrote in news: snipped-for-privacy@hotmail.com:

For a 110V type at 1700 lumens, perhaps. 240V types only put 1200 lumens.

More like 6-7%. Each watt of tungsten radiation in the 400-700 nm range is around 250 lumens.

Figure around 250-300 lumens per watt of "white LED light". Looks like those achieve about 20%.

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

So why do Cree, and Wikipedia, and probably many others, cite only 17 l/W? Every time I've seen the efficiency expressed as a percentage it's been '1 to 2%'. Wikipedia state 2.6% which is a tad higher than I've ever been told before, and even that's nowhere near 6-7%! It's not going to be easy to learn if everywhere I turn there are figures differing by factors of three or more. What makes all the others I've seen wrong?

I have a homebrew BASIC program with the blackbody function and the photopic function.

A USA-usual "Big-3" brand 100W 120V "standard frost" or clear incandescent rated 750 hours average life and with a coiled-coil filament is rated to produce 1710-1750 lumens, traditionally 1710. (The "Soft White" version achieves 40 lumens less.) The color temperature of that one is 2865 K.

My homebrew program says 16.7 lumens per watt (pretty close) and that

The discrepancy is caused by tungsten having emissivity varying with wavelength - generally inversely. Infrared radiation is suppressed enough to get 17.1 lumens/watt instead of 16.7 despite the lamp having some heat conduction loss. (For that matter, color temperature does not exactly match filament temperature - filament temperature is slightly lower.)

So an ideal blackbody at 2865 K receiving 100 watts and radiating 100% of this produces 6.63 watts of visible light and 1670 lumens. The ratio of lumens to watts of visible output is 252, not 683. 683 lumens in a watt of visible light is only true for yellow-green light of wavelength around 555-556 nanometers, where this figure is maximized. Those saying that incandescents are only around 2% efficient are assuming that a watt of any kind of visible light has 683 lumens.

Assuming my 252 lumens per watt figure for the visible portion of 2865K blackbody radiation is true for a 1710 lumen 100 watt lightbulb, that means a 1710 lumen 100 watt lightbulb is about 6.8% efficient at converting electrical power to visible light (400-700 nm). The truth won't be far from this.

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

This makes sense, in a way, though the actual assumption is surely a misinterpretation. In the context of lasers it makes sense now, because those are usually monochromatic (or take pumping on narrow bands of lines), and the maximum efficiency of any 'line' drawn from that lamp will be around 2% at best. Discussions of efficiency for narrow bands or lines in lasers or LED's or phosphor or sodium sources dominate a lot of reference material, so that's probably why this figure arises so often.

Even so, it's harder to see how that hasn't been corrected in something like Wikipedia by now. I guess a lot of people don't think of light below

A lot of the heat energy is carried to the bulb by convection and emitted as IR, so the temperature will be lower than than if the filament was heated in vaccuum. It's not an ideal blackbody radiator. That could make a likely average fall well below 6%, especially if you consider that the world has a lot of 240V lamps too. The steepness of that curve alone is enough to make large changes in output of visible lumens with small changes in voltage.

In short, I guess that the figure of 2.6% and others similar might not have been gained by calculation at all, but by measurement. I don't know what the conditions for that were though, so I can't comment on them.

Wikipedia articles are written by anyone who wants to write them, and with a few exceptions can be edited by anyone who wants to go in and edit them - anonymously even, without even creating an account and signing in.

Tungsten deviates from blackbody largely by some supression of infrared, enough to slightly outweigh heat conduction and convection by the fill gas in some incandescents.

I think 240V 1000 hour 100 watt would be more like about 5.5%.

Yes, quite true. But at full voltage most 120V incandescents 60 watts or more are about 4.5-8% efficient at converting electricity to radiation in the 400-700 nm range.

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Of course. It's also more likely that such an item would be corrected than vandalised. If we were wanting a verdict on the mental health of Micheal Jackson the laso place I'd expect to find a sensible judgement would be Wikipedia but for technical things that don't have any salacious or celebrity entertainment value it's fairly good, or at least likely to improve over time.

It's not the only source I rely on either. It's actually slow to load and not the first I turn to, most times.

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Is this by calculation or measurement? I was hoping you or someone else would comment on that from experience with it. Those lower figures are so common that they must have come from somewhere, and not all from looking only at the strongest wavelength or omitting something in calculation. I've never seen claims of 6 to 7% for a 100W lightbulb before, and I'm sure I would if measurements routinely reported it.

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Watts of emitted light? I just saw a later post of yours that mentioned "lumens per visible radiated watt". I think that's why we're discussing such different values. I'm talking about input watts. I thought we all were, at least Eeyore certainly was, as that's ultimately watt (haha) is consumed no matter watt is emitted.

Cree themselves don't claim anything like 250-300 l/W for input watts, at least not yet, though that might not be long awaiting.

So how does a 100W incandescent look in that context?

They do lots of photometric measurements, while radiometric figures for incandescents appear to me to be rather rare. More common than actual measurements I see comments in the direction of "close enough to blackbody".

Osram says 5% here:

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

I am saying that a watt of white light is about 250 lumens, not the 683 some use as the lumen/watt figure for a 100% efficient light source. A

Most of those generating figures of incandescents being 1-2% efficient are assuming that they would achieve 683 lumens/watt if they were 100% efficient.

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

Ok, I see that lumens depend on the spectrum, not just the actual visible watts emitted, but given that there is convection in an incandescent lamp that makes some of its power emit in the IR, does enough leave that way to bring the lumens per input watts down to levels that can account for stated line-power-to-light efficiences of 3% and lower?

I think when Cree talk of lumens per watt, they're talking of lumens for each watt of electrical input, and that's how I want to make the comparison.

Most of the output of an incandescent is IR.

I was only mentioning figures of lumens per watt of visible light output to explain that an incandescent achieving 17.1 lumens per input watt is nearly 7% efficient.

Put 100 watts into an incandescent that chieves 17.1 lpw. You get 1710 lumens. Each lumen is about 1/250 watt of "white light", not the 1/683 watt assumed by those claiming incandescents are only 1-2% efficient.

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

What I meant was, might more heat be carried away by the convection in the argon fill, and be either conducted or radiated away at far longer wavelengths? I mentioned convection specifically to be clear I'm not talking about directly radiated energy.

I've managed unintentionally to get you to say that three times now. :) I'm not always quick on the uptake, but I try... what I'm getting at, is can any other evaluation result in that lower figure? I'm not convinced that taking only the lumens at 555 nm accounts for this. Lumens seem slippery enough if they depend on spectra and photopic sensitivity anyway.

Wikipedia again: "In photometry, luminous flux or luminous power is the measure of the perceived power of light. It differs from radiant flux, the measure of the total power of light emitted, in that luminous flux is adjusted to reflect the varying sensitivity of the human eye to different wavelengths of light."

I guess that much can be relied on. So try it this way:

Take a 100W incandescent, and a large ellipsoidal mirror to gather as much of its radiant flux as you can, throwing it to the other focus of the ellipse where a black painted thermopile awaits. The incoming light is passed through a dichroic filter at 700 nm to send the IR elsewhere and pass only the visible light to the thermopile. Assuming you get close to ideal light gathering for the visible wavelengths (and IR rejection), how many watts will be read from the thermopile?

I understand that photometric measurements abount, and radiometric ones are rarer, but that's what I want to look at, as without that grounding the rest seems most insecure.

As far as I understand what goes on there, around 10-15 watts is convected from the filament in a 100 watt "USA-usual" "standard" A19.

I believe some who are not aware that the lumen is a unit of luminous and not radiant flux, or not aware of visible wavelengths other than 555 nm having less than 683 lumens per watt, divided a lumen/watt efficacy figure by 683 to come up with incandescents being only 1-2% or 2.6% efficient.

I expect about 6.7 watts in the case of a 1710 lumen 100W incandescent, if the ellipsoidal mirror is a whole ellipsoid and 100% reflective and the dichroic filter passes all 400-700 nm light.

As for the rest, approximately or "educated guesses":

UV passing through the glass: .12% UV absorbed by the glass: .02%

Heat conducted/convected from the filament: ~13%

IR passing through the glass: ~60% IR absorbed by the glass: ~20.16% ("rounded oddly" to make figures add to

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

snipped-for-privacy@manx.misty.com (Don Klipstein) wrote in news: snipped-for-privacy@manx.misty.com:

I was trying to keep the lumens out of this entirely, but I'll buy it. :) It makes me wonder what the fuss is about actually. While it's better to get more efficiency, it seems that incandescents aren't so bad we need to consider banning them, we just need to think more about what source we use for a given task. As for the case to ban all but halogen types, how much might be gained? With IR reflection to make them keep the tungsten hotter for a given input, we get more light, but even so, is there that much difference? Enough to say that they stay and standard incandescents go?

If LED's ever get a spectral match for a small efficient low-volt halogen, at least the choice will be easy.

OK, I'm following all this - just about, I think. So let me now throw in a slightly new set of questions. Back to LED halogen substitutes. Some distance back up the thread, consideration was being given to losses in the control circuitry for the LEDs. So, the first question is, just exactly how are these things ballasted ? The reason that I ask this is that I was in an electrical cash and carry warehouse tonight, and I picked up a couple of LED-based GU10 replacements to have a look at. I didn't count the actual LEDs, but I'm guessing at about 15 or so - let's say 15. Let's also say that they are bluish types and let's guess at a forward drop of 4 volts. With them all in series, that's going to be around 60v DC that's needed to run them.

Now, these lamps were of exactly the same dimensions as a standard GU10 lamp, with the same 'nail head' pins, set in the identical ceramic base.

Next question. There were two types on offer, one rated at 1 watt, and one at 1.3 watts, both with a quoted lifetime of 50k hours. So what exactly is being said here ? Is that 1 watt input from the mains supply, or 1 watt used by the LEDs or 1 watt of visible luminous output power ? A website that I looked at quoted the output of a 0.62 watt one, at 20-30 l - I'm assuming that to be 'lumens'. If correct, and not a misprint, that seems to be a piddling amount compared to the 950 lumens quoted for an incandescent 240v

Setting aside the issues of colour temperature and CRI, which I am sure will shortly be overcome, it seems to me that these halogen replacement lamps are even now on their way to bettering CFLs in that they are already exactly the same pattern as the lamps that they are replacing, so must have sorted the ballasting problem. And yet there are no plans to phase out the incandescent version. This flies directly in the face of the proposals to ban standard incandescents, when the advocated replacement technology (CFLs) is far from being a satisfactory replacement, on several counts.

Arfa

"Arfa Daily" wrote in news:Fweli.25909$ snipped-for-privacy@newsfe5-win.ntli.net:

There might.. First, it needs to control a fixed current, and an efficient power converter can be tiny, flat, like this:

That one sounds like a marketing hype. The first thing is that it has lots of standard 5mm LED's. Avoid like the PLAGUE, seriously. All that voltage drop, and no cooling to speak off, what kind of thermal coupling can be had for a 5mm LED?

The ones to look for are the Cree and Luxeon types. The easiest way to look for them is a single emitter, or at least very few of them, with high output claims. Look into one (unlit!, they WILL damage your eyes if you do that to lit ones at close range), amd you'll see a distinctive fluorecent dayglo green yellow cast to the phosphor unlike the chalky phosphors of weaker white LED's.

Re wattage claims, it's hard to say, without evaluating all the evidence you can find together. In short, a lamp that needs several emitters to manage 30 lumens is a joke, when you can cheaply get a single emitter that puts out >200 lumens with 1 amp pushed through a voltage drop of around 3 volts.

I think the ban is 'being seen to be done' kind of reaction. It's got more to do with trashing an icon known for inefficiency, but there are better ways to make people change than all-stick-no-carrot.

If governments really want to reduce power consumption I think they should be subsidising the public to buy computer mainboards based on Nehemiah CPU's and such. Turning a domestic computer into a fan heater just to run Windows Vista as a private office is a sick joke! Far more worrying than a few lightbulbs.

I don't have a problem with a switch mode converter being small - just with the front end to get from 240v AC down to some realistic DC level, also being small. I work with switch mode power supplies of every size on a daily basis, but I've yet to see the front-end electrolytic, which would fit in any space that was closed in so that you couldn't see it, on one of those GU10-s.

As far as 5mm LEDs needing a lot of cooling, I've played with all manner of superbright emitters from white thru' traffic light colours all the way to red, in 'standard' packages, and never found cooling to be especially a problem. Although these are not hyper bright Luxeon-style emitters that I'm talking here, which I know *do* require external cooling, They are never-the-less still bright enough to hurt your eyes, and light a dark room up quite well. Where I have found theremal issues, is in the current control circuitry, even if just a simple resistor.

I agree that the potential ban on incandescents is just a government knee-jerk reaction, brought on by hysterical claims from their 'scientific advisors' that these things are going to bring about the end of the world, but not if we use the marvelous direct replacement CFLs instead (ha!) ... I was just interested what others' opinions on this were.

So, I'm still no closer to knowing how the multi-LED GU10-s or even single LED types, are actually ballasted for 240v AC use, and whether the claim that "these lamps put out almost no heat at all" is at least basically true overall, in which case the ballasting arrangement must be *very* efficient, or refers specifically to forward IR radiation in the same direction as the light, which obviously will be minimal, or is a fundamental marketing hype lie. Maybe I'll just buy one, and see if I can figure out just what its guts are.

Arfa