Text-Alternative Version: Understanding and Evaluating LM-79 Reports
Below is the text-alternative version of Day 1 of the three-part TINSSL Webinar Series "Understanding and Evaluating LM-79 & LM-80 Reports for SSL Technology," held August 10, 2010.
Sarah Eckstein: Today's webinar will focus on understanding and evaluating LM-79 reports. Tomorrow's webinar will focus on understanding and evaluating in situ temperature and measurement points and LM-80 reports. On Thursday, just take notice of the time change for this particular one.
What you will have learned in Days 1 and 2 together, we'll be walking through examples of real test support on Day 3. Before we move on to today's webinar, I would like to give you a quick overview on who NEEP is, what NEEP provides through the Technical Information Network for Solid-State Lighting, and what the DesignLightsTM Consortium for Qualified Products List is because Jason will be referencing this program in his presentation.
So, after presenting these three slides, I will introduce Jason Tuenge and Kelly Gordon.
Hey, Terry, it's not letting me—whoops, there we go, it's up there, just kidding. So, NEEP is a regional energy efficiency nonprofit that collaborates with policy makers, energy efficiency programs, and industry to accelerate the use of energy efficiency in buildings and homes.
The Technical Information Network for Solid-State Lighting, also known as TINSSL, increases the awareness of solid-state lighting technology, performance, and applications. NEEP has received a grant from the Department of Energy to deploy information and dissemination related to solid-state lighting.
TINSSL members, who make up a very broad audience, receive updates on solid-state lighting technologies and opportunities to participate in educational webinars such as this one.
One of the other activities I would like to mention that NEEP is heavily involved in is the DesignLights Consortium for Qualified Products with projects.
Sorry, my screen is a little slow. And so, the DesignLights Consortium for Qualified Products with projects needs the role interplay of the project manager, which collaborates with 26 utilities and energy efficiency programs, along with working with the contractor that was hired to evaluate and verify the manufacturer's test data.
And the main purpose of setting this project up was to build a prescriptive list of commercial LED lighting products, to really weed out the junk versus the high-quality, high-efficient LED products.
So, without further ado, I would like to introduce our main presenter for today's webcast, Jason Tuenge. Jason joined PNNL in 2008, and has ten years of experience in the lighting industry. He provides lighting engineering support for DOE's activities within the commercial building initiative and market-based programs for solid-state lighting.
Jason also manages the technology fact sheets program, producing educational material on topics ranging from solid-state lighting itself to human factors and economics.
I'd also like to introduce Kelly Gordon, who will support the Q&A portion of today's webinar. Kelly Gordon has been with PNNL since 2000, and has more than 20 years of experience in the energy efficiency field, with a particular focus on efficient lighting technologies.
Kelly currently manages PNNL's activities related to DOE's L PrizeSM competition, and was further involved in the development of the DOE ENERGY STAR criteria for solid-state lighting luminaires and integral replacement lamps.
So, without further ado, Jason, I'll hand it over to you.
Jason Tuenge: All right, thanks, Sarah. Can everybody hear me fine?
Speaker 1: Yep, I can.
Jason Tuenge: Okey-doke.
Speaker 2: Yeah.
Jason Tuenge: I'm going to go ahead and mute the lines, and we'll get started here. Okay, I still hear some background noise.
Speaker 3: Where somebody wanted a long/short, long/short.
Speaker 4: But that's what it is?
Speaker 3: Oh, yeah, it's ridiculous.
Jason Tuenge: Shoot. Terry, any idea why we still hear people in the background? All right, well, I did mute the lines. Hopefully we don't get any more noise. So, I'll try doing it again.
Okay, so over the next three days, we're going to be going over the connection between LM-79 and LM-80, discussing how to review those reports and make sense of the two in terms of how they relate to each other.
I'm sure most of you are already familiar with what LM-79 is. Basically, it's a relatively new standard developed specifically for solid-state lighting products. There are a number of similar standards for incandescent or metal halide or fluorescent lamps or luminaires. Now we've got one specifically for LED products.
And this document, as you can see, is indicated really just for integral lamp products or luminaires, not intended for the light sources that go into either lamp or luminaire. In other words, not for modules or packages. You know, the LEDs themselves.
So, along the way, as we've been—as this technology has been maturing, we've needed to develop some new terminology to characterize some of the performance aspects, and at the same time, relied on a lot of existing terminology metrics equipment.
But now we find ourselves taking a much closer look at a lot of these terms. Where we just kind of took them for granted before, now we're finding we have to look at them more closely to make sense of it all.
So, basically this standard addresses test conditions and measurement methods. It does cover the measurement of special power distribution, like the diagram you see over on the right. Typically, this data is gathered in an integrating sphere, you know, an old technology, where basically you draw up your source into the sphere and out comes your total output measurement, total lumen output, and you can also capture chromaticity in special power distribution.
From this data, you can calculate correlated color temperature; Duv, which is a new metric for solid-state lighting; color rendering index, which is well known, been around for quite a while; and a relatively new metric that you might see in some of these reports is the color quality scale. This is something intended as an alternative to CRI, given some recent—you know, recently exposed flaws in CRI as exhibited when measuring CRI for LED products.
Something else that you can get, or something else that's standardized in LM-79 is measuring the spatial distribution you get from sources. And this is typically done using a goniophotometer, where basically a mirror and/or a sensor are moved around in space around the fixture, or the fixture itself might be turned around in space so you can capture how much light is going in each given direction, and this is—you cannot get this with an integrating sphere. You have to do it on a goniophotometer, where things are moving to capture this sort of data.
And this is how we calculate things like zonal lumens, bug ratings. It's worth noting that when you do calculate your total output from one of these, you are doing some interpolation for your total output. But typically, you go with your sphere data for this sort of thing.
It also addresses measurement of total electrical input to the system, to the lamp or the luminaire, and from this then, you can calculate your efficacy. And as I mentioned before, this shows basically, you know, since you are capturing data to a number of points, your intensity data, you're end up having to interpolate, and that introduces some error for calculating your total output. Better to go with an integrating sphere for this sort of thing.
LM-79 does not address measurement of LED drive current. This is a very common point of confusion. Just because you see a current value given doesn't mean that's what's actually passing through a given LED module or package. What you see reported is typically the input current to the driver or drivers that are contained within a luminaire or a lamp. So, it's really just the input to the lamp or luminaire, not to a given LED in an array in the lamp or luminaire.
LM-79 does not cover in situ temperature measurements. So, your temperature measurement point is not given any attention in LM-79. That's covered in a separate test, the ISTMT, which we'll get into tomorrow.
LM-79, as many of you know, does not cover lumen or color maintenance. This is covered by LM-80, which again will be covered tomorrow, or which also will be covered tomorrow.
LM-79 does not standardize report format or content, as many of you have noticed. You see all sorts of different arrangements of data, and this can make it difficult to compare performance between products, and also to quickly determine whether you're missing data. Sometimes you end up with just color data.
I'm hearing some noise in the background, so everybody make sure you've got your lines muted.
So, you might in your report only see color data, or you might only see spatial data. So, it would be nice if LM-79 covered this sort of thing, but it does not at this time.
Reports also do not indicate the make/model information, the catalog number, or the LEDs themselves within a lamp or a luminaire. This would be useful for evaluating LM-80, but this is very difficult to do accurately and reliably capture.
And last year, we've got some—it's good to know you're off the power draw, but this is not by default included in most reports. You have to request that especially.
In LM-79, they do offer typical items reported.
Again, I'm getting a lot of background noise. Somebody thinks they're muted, but they're not.
So again, here we've got a listing of typical items reported per LM-79. So, this is basically like a suggested items list for inclusion in reports, but not mandatory.
And continued—and we'll get into some of these here in the next few slides. So, a good example of a set of criteria for LED products is given by the DesignLights Consortium that Sarah described.
Here we've got requirements presented in tabular format, so we can just look around the column heading to see that what they've focused on are total output, zonal, you know, basically your lighting distribution, your luminaire efficacy, correlated color temperature, and CRI, and lumen maintenance.
The last one, lumen maintenance, is not covered by LM-79. We'll get the others.
There we go. Make sure I didn't skip a slide.
So, when you get a report, you will pretty much always see total lumen output reported somewhere. You may not see distribution—you know, intensity distribution somewhere in your report, but you typically should see that somewhere, especially if you're actually looking at the distribution in terms of your own criteria.
Just because you get zonal lumen reporting doesn't mean you get exactly what you need. In the case of NEEP, one thing they're looking at is the lumens and the zone from 80 to 90. So, here you'd have to do simple addition of seven and three, and I think I can highlight that here—of seven and three, and then divide by the rest to—or divide by the overall to get your percentage in that zone for their requirement.
So, you don't always get exactly what you want. Some just do a few hand calcs.
You'll also see diagrams like this, characterizing basically the color of the light that's being produced by your source. This can be given in terms of XY coordinates, or U prime/V prime coordinates. You'll also see the correlated color temperature. And since we're looking at solid-state lighting products, you could see Duv reported as well.
Basically, the curve that we're seeing in black, which I'll trace here, is basically tracking a black-body radiator, kind of like a tungsten filament in an incandescent lamp as it heats up, it goes from red to blue. Something that many of us are already familiar with, but this is how we characterize some of the—
Yeah, I'm gonna go ahead and try re-muting apparently. That's not working for us.
Terry Shoemaker: Jason?
Jason Tuenge: Okay, let's see if it does the trick that time. All right, so basically the CCT just tracks along this black-body curve, and then Duv is used to quantify how far off the curve you might fall. So, you might end up—let's see if I can choose a color here. Well, I think this will probably work for now.
If you end up below the curve, you could end up with a color that's fairly pinkish. And if you're above the curve, you can end up kind of greenish, which is definitely undesirable. So, this is information we try to capture.
The document that we reference in characterizing the color traits of LED products is this NEMA document, which is an ANSI standard. And this does a good job of describing and graphically illustrating how this all works, where before, in the past, we've used MacAdam ellipses to characterize things like fluorescent lamps, and now we're using quadrangles. And your chromaticity coordinates have to fall within one of these quadrangles.
So, an example—oh, sorry. So, basically, this is broken down in tabular format, as you can see here. If you've got, for example, a 3,000K nominal lamp, then actually what you're shooting for is 3045K or 3,045K, plus or minus 175. And then Duv shoots for 0, which means right on that black-body curve and—let me highlight this for you—and then you can be plus or minus .06 from there.
So, taking an example using the flexible CCT, which is shown at the bottom of the table down here, and which, by the way, is actually not used by ENERGY STAR or NEEP, but this just gives a good illustration of how this works for other chromaticities as well.
Basically what's shown here is a 3,200K nominal source. And you've got the points shown right here(ish). This highlighter's a really heavy line weight, and I'm not sure how to change that, sorry. Then you've got the point landing very close to the curve and thereby meeting our requirements. You know, Duv is .02, landing within the required range.
Something else you'll hear mentioned quite a bit is absolute photometry required for LEDs, whereas other sources tend not to be overly sensitive to temperature. You know, other lamps tend not to be overly sensitive to temperature. LEDs are extremely sensitive to temperature. This is why you see so much attention given to thermal management on LED products.
With other products, like fluorescent or HID, you test the lamp, the ballast, and the luminaire separately so you can mix and match parts and pieces and still have a good idea of what you're gonna get when you actually combine them together and sell them on your site.
And so, things like luminaire efficiency, rated lamp lumens, and ballast factor have meaning when you're dealing with relative photometry. This also reduces the amount of testing. One thing worth mentioning is that when T5HO lamps were first introduced, a number of you probably noticed that you ended up with luminaires rated over 100 percent efficiency. And this was due, actually, to these thermal impacts and some confusion over ratings.
And so, it's not just LED, but LED is especially sensitive to temperature. And so, we look for absolute photometry for LED products, where you do not test the sources, the drivers, and the luminaires separately. It's all integral in one test. And if you change anything, you need to retest the whole thing as a complete system.
So, again, this heat sensitivity is the reason why you see these heat sinks on products like the one shown at the top right here, a track light. And this is also why you don't see things like efficiency calculated, because it has no meaning for an LED product since there's no rated lamp lumens.
So, potentially, this entails quite a bit of testing for LED products, which are already expensive as it is. Right? Given—you know, so understanding this, ENERGY STAR and others do allow conservative testing, where you basically test your worst case, and then allow a lot of other cases to then follow with the same test, knowing that they actually outperform the one that's been submitted.
So, basically here you can see a description form ENERGY STAR saying that a number of things are fine so long as the LED packages remain the same, drive current is the same, electronics, thermal management. As long as those are all the same, you can make other minor changes and submit as part of a family.
One thing worth noting is that you can change your optics. And so there's some potential for gaming here for manufacturers, where, you know, they could in theory submit a clear lens fixture and then, as part of the family, tagalong with some other opaque lens fixtures that clearly don't perform as well. So, you need to watch out for these sort of things.
Here's some additional information again clarifying that optics are basically left to the discretion of the manufacturer. And if so, again, there's potential here for gaming if you're not really paying attention.
And then NEEP, you know, the DesignLights Consortium, for the Qualified Products List, their set of criteria, they made a couple clarifications really in line with ENERGY STAR criteria. You know, for example, if you paint your housing a different color, that is not a problem. And if you've got one optic that directs light left and another one that goes right, but they're symmetric to each other, then you can, of course, just test the one side. You don't have to test both sides.
ENERGY STAR and NEEP both require testing by a qualified test lab. This is not part of LM-79. It does not state this in LM-79. You have to have testing done by a qualified test lab. For the time being, the best place to go is this link provided here. This is the CALiPER page for test labs.
At some point, NVLAP will be catching up, and we want to see NVLAP certification of all these labs, and that will ultimately lead to manufacturers actually being able to do some of this testing. If they can demonstrate that their lab behaves independently from, say, the sales branch of their operation.
You want to take a look at—I'm sorry, I didn't flag here that we're just getting into this checklist that we're gonna be providing at the end of today's and tomorrow's webinars, and then implementing fully, and the last on Wednesday walk through some of these—some sample submittals—and see how you can go through a review process with confidence, knowing that you've covered all your bases, checked all the things you need to check.
So, getting back to this, one thing you want to do is make sure that you're looking at something that does not appear to have been manipulated. One thing to do is to request the original report from the laboratory in PDF format.
This, like many other things, can be gained. You know, for example, a manufacturer could suppress a word document from a lab, modify it, and print PDF. So, this is not a guarantee that has not been manipulated. But this sort of thing can help discourage some of this editing. You might actually request data come directly from the lab by e-mail, rather than from the manufacturer, if you're really worried about it.
Here is an example of one manufacturer that's actually very forthcoming about the fact that they changed—or that they incorporated the report into their own report and kinda rearranged information for their own desired presentation. You won't always find this kind of a statement on these kind of manufacturer private reports.
One thing that is really key is—and really difficult, as it turns out—is to be sure that you're looking at something that really pertains to the product that was submitted. Often what happens is you'll have a manufacturer submit a product to a test lab. They'll give some catalog number, but then it was either temporary or partial or something, and then when they submit to you, they give you a complete catalog number, and then it's up to you decide whether that test really even applies to the product they submitted.
In a perfect world, they would submit the exact same catalog number at the test lab. They can include that in their report, so then you can just simply match the two up and say, "Yes, this is the same thing that was tested that I'm now reviewing." This doesn't always happen, and you have to use some judgment or simply force the manufacturer to make things right so that you can compare these items in confidence.
You also want to go looking through the descriptive text to make sure that everything lines up—input current to the product; the voltage that it's operating at; the wattage that it's drawing; number of LEDs, if that's reported; the drive current, if that's reported. Again, drive current is not measured as part of LM-79.
CCT, the optics, take a look at it and make sure that they haven't tested with clear lens and submitted with opaque, or try to tagalong opaque as part of a family when all that was tested was clear. Also, make sure that there's no thermal management that's not indicated on the cut sheet.
This was a comical but scary example that I stumbled across while reviewing an IES file from a manufacturer, where, hard to believe, where some manufacturers will come right out and say, "Yeah, we've got the best fan on the planet to keep our LEDs cool." Some will apparently actually take a product that has no fan and then when they submit it for testing, they'll attach a fan to it. Then hopefully, again using a qualified testing laboratory, they won't hide this fact. They'll clearly state it in their report, and maybe even take a photo, just to make sure nobody misses this point.
And so, here was something where this text had been removed from everything else but the IES file, and I caught it in the IES file, where they'd actually attached a cooling fan to this product, which would clearly give it a performance advantage at least in data.
Something else that was at least a problem early on in the process because we were dealing with some new metrics were some errors that were being introduced by our trusted test labs because they're human, and some of these new metrics required some hand calculations.
You know, they use software to generate most of the reports, but then some things like power factor and efficacy weren't necessarily calculated like other product types. Now we want them for LED. And so, we did notice a few errors here and there. So, it's good to do a spot check just to make sure that there isn't an error of the sort shown here, where basically the efficacy that was reported was not actually the efficacy you get by doing a quick hand calculation.
So, that wraps up the material for today's presentation. Basically, tomorrow we're gonna be following up, as I indicated earlier, with an overview of ISTMT and LM-80 reports. These basically complete the process when you're using the ENERGY STAR option one compliance pass for lumen maintenance and color maintenance.
This is something that may be somewhat in flux in the near future. You know, ENERGY STAR, as I'm sure many of you know, is now under EPA, and so some of this may change. Certain product types may be exclusively Option 2, and so that you may not even have the choice of dealing with LM-80 data for certain product types. Under Option 2, you simply test LM-79 twice—once at 0 hours, and then again after 6,000 hours of operation under the appropriate environment as per ENERGY STAR.
We're gonna just focus over these next days just on option one, tying together LM-79, ISTMT, and LM-80. Again, one variable that gets overlooked quite a bit is drive current. And so, that's something else that we need to make sure to look out for in particular just 'cause you have your LM-79, ISTMT, and LM-80 doesn't mean you've got drive current really pinned down. So, be paying attention to that.
And that is all for today. At this point, I'm gonna go ahead and open up the phone lines.
Terry Shoemaker: Jason? Jason?
Jason Tuenge: Okay, so everybody should be live, and if we run into problems, please—I'll have to re-mute everybody, and then please submit your questions through your Q&A off the window. So, now we're all live.
Terry Shoemaker: Jason, can you hear me?
Jason Tuenge: I can hear you, Terry.
Terry Shoemaker: Thank you.
Jason Tuenge: Okay, so we're gonna open it up now to questions. Let's try to keep it one at a time, and if it gets too crazy, we'll go ahead and mute as I was saying. Are there any questions? I hear background noise. I'm pretty sure we've got people online.
Kelly, are you on?
Kelly Gordon: I think so. Can you hear me?
Jason Tuenge: Yep, I can hear you. Well, I think we've got everybody. Apparently not a single question.
Terry Shoemaker: Jason?
Jason Tuenge: Uh-huh?
Terry Shoemaker: We did have one question come in through the Q&A page.
Jason Tuenge: Okay, I'll switch over to that. I don't see a question, actually.
Terry Shoemaker: It's, "Which test, if any, addresses color shift over time for SSL lamps?"
Jason Tuenge: Oh, okay. Yes, color shift over time is addressed by LM-80, which we'll be getting into tomorrow. Well, and actually, for the—so, I guess to clarify that, and again, I'll get into it more tomorrow, but, you know, for a complete lamp, you would be looking at doing the Option 2 compliance path, where, you know, you actually test the whole product. Once the LM-79 at 0 hours operation and then again at 6,000 hours of operation, and then just track the shift over time. That'll be for the whole product.
But again this is gonna depend on where exactly things land. Kelly, correct me if I'm wrong, but I believe right now, as it stands, and this is fairly new, that the integral lamps indeed need to be tested this way, not using LM-80 data. But for other product types, and possibly in the future for integral lamps, depending on where things go, you'll see you can use LM-80 to track the color shift over time.
Kelly Gordon: Yes, LM-80 does address color maintenance over time, and integral lamps in the ENERGY STAR program do need to be tested as.
I believe there was another question that came in. Do you see that, Jason?
Jason Tuenge: Yes. Let's see here. Boy, actually for some reason, I seem to be lagging here. I'm gonna need some—
Kelly Gordon: Okay, it's under "Manage." It says, "Can you give more detail on interpreting the polar graph relating to zonal lumen?"
Jason Tuenge: Oh, okay. Let me switch back over to it. Okay. So, basically—well, I guess the lines are open, and so if I'm not quite clear, feel free to speak up or go ahead and submit again in writing. But basically, intensity is just lumens per solid angle. And so, without actually breaking out a spreadsheet, it's kinda hard to really explain exactly how it all fits together.
But basically, what you end up doing—on the left you can see we've got a fairly tight distribution. Right? So, we've got a punch downward. Let me see if I can use my drawing tool here very well. So, basically this is pointing downward. Right? And so we've got quite a bit of intensity going downward, and not much at all going out at the higher angles. Right?
And so, this is gonna be reflected when you look over in the zonal lumen summary. Over here, this 0 to 5 zone is more or less straight down, whereas this region here is, you know, the higher angle is closer to horizontal.
And so basically with a spreadsheet, you just—you take your intensity and your solid angle, which is kind of hard to explain without lots of hand waving and diagram drawing, take your lumens divided by your solid angle. That gives you your intensity. So, if you rearrange things, then you get your intensity times your solid angle is your lumen, given here. Actually, that's your percent. No, actually that is your lumen.
So, basically—yeah, you're gonna see basically both forms of information. You get your intensity on the left, which kind of gives you a sense of where the light's going, and then you see the zonal lumen summary, which is more generic. You lose, for example, where in a horizontal direction the light's going. Just kind of averages it into cone.
When you look at these regions, they're basically a series of concentric cones. Sorry if that sounds so alien, but it kind of looks like this, where you've got—you know, for the 0 to 5, you'd be looking at a cone that looks something like this, and then for—you know, it'd be covering the area inside here, the 0 to 5.
And then for the region from, say 85 to 90, you'd be looking at this region that's spun around—you know, around straight down. Then it's looking at these regions here. So, you just spin that around the funnel. So, hopefully that clears it up a little bit. I'm not fully prepared to give, like, an animated description of how the two relate to each other.
Kelly Gordon: Okay, we do have some additional questions coming in.
Jason Tuenge: Yeah?
Kelly Gordon: Okay, so do you want me to read this one, Jason?
Jason Tuenge: Sure.
Kelly Gordon: So, could you share some thoughts about outdoor pole top and surface mount SSL lighting performance? Some manufacturer data purport that SSL lighting does not adhere to the inverse square law describing lighting fall off over distance. Is their assertion correct? What progress are you expecting without outdoor SSL for lumen output going forward?
Jason Tuenge: Well, okay, I do see in front of me—let me make sure I can make sense of this. Yeah, I mean, wow. Okay, so that one's kind of all over the place. So, there are some things that are fairly new with LED. One thing that absolutely does not change is any of the laws of physics underlying photometry. That absolutely applies to LED just like everything else.
You know, something similar is you'll hear that, you know, in terms of spectrum, LED's a whole new game, and you can't really capture performance in an LM-79 report. We've got a number of comical voicemails here in the office from an individual along those lines.
And basically, the laws of physics have not been changed at all for LED. All we're really dealing with here is trying to deal with the thermal issues of LED. That's really the main trick. And there are some things that are tough to capture, like drive current of LEDs.
There's a few things like that that are just kind of hard to measure. But otherwise, when you get into things like the inverse square law, which is just how you calculate illuminance, then there's no change. The only thing that you could potentially run into is if you've got—and this can happen for fluorescent as well—if you run into issues with, say, near-field photometry, you know, or the five times rule falls apart. You know? So, that's not LED, that's just for a big source that's really close to a surface.
So, really there's nothing new there. Getting on to the point of output, yes. I mean, LED is definitely making great strides. Probably the main thing you run into when you start getting into really high output fixtures is that they need a lot of LEDs in there in order to do the job. And as a result, they get expensive. Right?
So, you know, whereas going from a 100-watt high-pressure sodium to a 1,000-watt high-pressure sodium doesn't add that much cost. You're going from a $15.00 lamp to a $40.00 lamp maybe. With LED, you make that same kind of a leap, and you increase your cost ten times. So, it's much more dramatic for LED. So, there's some barriers like that.
But you can already see that the LED's making great strides to moving up that wattage chain and becoming more competitive with higher-wattage HID lamps. And in certain applications, competitive, say, with fluorescent indoors. But yeah, it's still competitive. It's not necessarily outperforming other technologies, and certainly not by default.
Kelly Gordon: Okay, are you able to see the next question, Jason?
Jason Tuenge: Yes. Okay. So actually, Kelly is quite well versed in this one, I'm sure. Do you want to take that one?
Kelly Gordon: Which one are you talking about, the XY?
Jason Tuenge: This one is actually looking at the beam-angle lumens.
Kelly Gordon: Okay. I'll read the question. How does the zonal lumen data relate to how a manufacturer rates their beam angle on an LED reflector or MR16? For example, what does the percent of total lumens need to be at a given beam angle to classify on packaging a 25 beam angle versus a 120-degree beam angle?
Okay, so let's review what beam angle means. Beam angle is dealing with intensity. So, this is in candelas, not in lumens. And the beam angle is the point, the angle at which the intensity has dropped to 50 percent of the maximum intensity.
Usually, when you think about directional lamps, like PARs or MR16s, you would see the maximum center beam. So, sometimes that's called center beam candle power maximum beam candle power.
And then as you move out, if the lamp is pointing straight down, that's the zero angle. As you move out, away from that center beam, the angle at which the intensity is 50 percent, so that is the beam angle. And that can be measured using the goniophotometer to identify the beam angle.
And then the other—it says—another example, what is the beam angle of—
Jason Tuenge: We're getting a lot of background noise.
Kelly Gordon: Did someone want to add to that? Nope? Okay. Many manufacturers are using optics that provide a slot versus a slug, which is generally providing 120-degree beam angle. Now typically in our lamps and BR lamps, they are categorizing not as much by a beam angle, that it is more generally characterized as a flood lamp. Usually the PARs and MR16s are more specific in reporting their beam angle, and there are tolerances defined in ANSI standard C78.379 for how those beam angles are quoted.
Jason Tuenge: Hey, Kelly? I think I'm gonna go ahead and mute the lines.
Kelly Gordon: Okay.
Jason Tuenge: If you want to get yourself back in here in a second. Just give me one second.
Kelly Gordon: Okay.
Jason Tuenge: Okay, Kelly, go ahead.
Kelly Gordon: Can you hear me?
Jason Tuenge: Yes, I can hear you.
Kelly Gordon: Okay.
Jason Tuenge: Shall we go on to the next one, or were you still on that one?
Kelly Gordon: No, I think I'm done with that one.
Jason Tuenge: Okay. So, next up, I guess I'll take a whack at it, and if I leave anything, let me know if I miss anything: "Please explain in further detail why drive current is important."
Basically, there's consensus among all the major manufacturers that there are two critical components at least for evaluating the life-time of a LED product, the useful lifetime. One of these is the temperature basically, the junction temperature at which the LED's operating. And so, we need to measure somewhere that's correlated with the junction temperature so we can get an idea of how well the thermal management is working, how well heat's being drawn away from the LED. So, that's one thing.
And then another thing that's closely coupled with that and very much related with the temperature is the drive current. So, these are two things that, you know, if you're driving your LEDs too hard, or if they're overheating, or both, this really has an impact both on initial performance, so your measurements you're taking right now.
If the thing is running too hot, and being overdriven, it also then impacts how rapidly the thing deteriorates over time. So, you end up with less light, and possibly much less light very shortly after you begin operating it. So you might have a useful lifetime of only a week or a day if you're overdriving or overheating it.
Additionally, there's a pretty broad consensus that ambient temperature plays an important role. But apparently this is not unanimous among the major manufacturers. Sound good?
Kelly Gordon: Okay. And there's still the other question—maybe I'll just read it out: "Sometimes the LM-79 tests give only X and Y coordinates, and not Duv results. If I go to XY coordinate on the chromaticity diagram, it has hard to measure how far off the black-body line you are. Is there a formula we can use to make sure we are within the Duv tolerance?"
And Jason, you may know more on this, but yes, there is a way to convert from XY coordinates to the U prime/V prime coordinates and then to be able to calculate the distance from the black body. So, if you would want to email us, we can email you that information back.
Jason Tuenge: Yeah, we can do that, but I think it's probably a pretty fair thing to expect of the labs at this point.
Kelly Gordon: That's true.
Jason Tuenge: Yeah. Again, it's not mandatory. They don't have to do it, but at this point, they should all know that they should be providing that information.
Kelly Gordon: Okay. You want to take the next question, Jason?
Jason Tuenge: Which is, "Is there a move to standardize the LM-79, LM-80 report format?" This is definitely your turf, Kelly.
Kelly Gordon: Okay. Yeah, I think that that's recognized that that is desired. Now where it gets a little bit tricky is that the various independent test labs and even manufacturer test labs that do this testing may use different types of equipment and software to collect the data. And so, that's typically why you see differences in the way the information is presented, because they're not all using the same software or the same equipment.
But there have been some efforts now—with LM-79, for example, many of you are aware of the DOE's Lighting Facts® program, which has the Lighting Facts label, which presents five key attributes of LED lighting products. Now, the Lighting Facts program has developed a fairly simple cover sheet that collects some of the key information from LM-79 testing into a standardized format. So, that's one effort that gets kind of part of the way there.
For LM-80, we do not have a common reporting format at this point. I think it is a worthy goal to have such a format that would make it easier to evaluate this information.
Jason Tuenge: Yeah, I think it would be especially useful, given that we don't have independent test labs reporting information, so we have to give it that much closer scrutiny, if it is coming from the manufacturers.
Kelly Gordon: Right.
Jason Tuenge: I think, yeah, it would be especially nice with LM-80. Whoop— another one just came in: "Will this presentation be made available after the webinar?" So, where might this be found?
Terry was addressing this earlier on. I believe the audio—well, I don't know if it will be as an AV file. We've done that in the past.
Kelly Gordon: Okay, let Terry answer.
Jason Tuenge: Yeah.
Terry Shoemaker: Jason?
Jason Tuenge: Yes, I can hear you.
Terry Shoemaker: We will plan to post the .wmv or the video file in approximately one week on both of the DOE solid-state lighting and the NEEP Web sites. Since the presentation is in PowerPoint right now in a large format, we can generate a PDF. It'll take a couple days to get it posted, but we could also send that out upon request.
Jason Tuenge: Thanks, Terry. Any more questions? We've actually got this blocked out 'til 10: 30, don't we?
Kelly Gordon: Okay, another question has come in.
Jason Tuenge: All right, I see it. "Will SSL tests show a CRI equivalent for users who are more familiar with CRI? Is ultraviolet light or any other negative attribute present with SSL that might be incompatible with a museum environment for gallery installation?"
This is interesting, 'cause we were actually just recently looking into this. We don't have anything formal to present on the latter item at the moment, but we have done some preliminary investigation.
So, as far as a CRI equivalent, so as I indicated earlier on, CRI is, by all means, still the default value given in LM-79 reports. There it is. Whoops—there.
So, basically, CRI will still be shown probably for quite some time for LED products. It is not necessarily the best metric for LED products, especially if you're dealing with RGB color mixing products. It's been shown to be a very poor metric, actually, in terms of capturing a user's preference for the color of light coming out of a source in terms of how it renders objects.
They find LED products—they can—they have shown that LED products with very poor CRI are actually preferred by people using lighting products. So, that's why the CQS metric was developed, was to try to explain why this happens and to come up with a metric that prevents that sort of confusion, so that if you have a high CQS, then people that buy the products will likely be happy with the end result.
So, currently, I'm not aware of labs reporting CQS. This is given mostly just as kind of a warning that, you know, you're probably gonna start seeing this showing up on reports, and in criteria. Now for the time being, it's really gonna be CRI, and you just have to watch out for it 'cause CRI, again, does not necessarily give you a true measure of LED performance in terms of color rendition.
Then getting back to museum lighting, where obviously you're very concerned about color rendition, basically what we've found so far, and the findings are definitely limited, I think we've all heard that you get no UV out of LED products. This doesn't appear to be entirely true. There is a small amount of UV. But from what we can tell, this amount is comparable to the amount you get from other sources after you add a UV filter, which means there's still some UV even out of a filtered incandescent lamp, or halogen.
But just with a bare LED, you're already down kind of in that neighborhood. So, we still need to do more investigation here to really capture—and with appropriate photometers that are designed to measure UV specifically—exactly what we're getting down in that range from one source type to another.
But at this point, it seems pretty—you know, by and large, looking at a wide variety of sources, that there really is not much UV at all coming out of LED sources. There may be other spectral concerns. You know, it may not render the way you want it to. If you've got certain materials that are especially sensitive at certain wavelengths, then you want to be aware of that and make sure you don't match it up with the wrong source, be it LED, incandescent, or fluorescent. You want to pay attention. You want to match your source with the material you're lighting.
That should about do it for that question.
Kelly Gordon: Okay, I don't see any additional questions at this time. Is there anyone on the line who would like to ask a question? Okay. We may be able to move through wrap-up then.
Jason Tuenge: All right, last chance everybody. Going once, going twice. Nope? Let's go ahead and close up shop then. Thank you everyone for attending. I hope you found this useful. And I hope we will see you again tomorrow and on Thursday as well as we go through our overview of ISTMT and LM-80 reports and then walking through our checklists, to see how you can actually review this information, which is a lot to deal with, in kind of an organized manner, and leave feeling like you've actually covered all your bases.
So, again, thank you everyone, and hope to see you tomorrow.