Posts Tagged ‘SSL’

In my previous entries regarding the Cree LR6, I’ve noted the good and bad sides of the product in some detail. I’ve noted my dissatisfaction with the brightness of the diffuser, which has caused me to first apply plastic trim rings to add a little cutoff, then later, to simply not turn them on. Dimming performance over the years has been disappointing as well. No dimmer I have found has dimmed them satisfactorily, most cause them to flicker. The latest from Lutron, designed specifically for LED/CFL sources, did not fix the issues, so I simply gave up. Rather than remove these expensive retrofits ($65.00+ each), I chose to do what many of us do when caught in a  quandary – stopped using them at all. Estimating these were not used more than an average of 1 hour a day for the last 4 years, total operating time is less than 1,500 hours. I’ll give them 2,000hrs, assuming that when they were first put in place, I used them more than I did as we grew tired of their glare and flickering under dimmer control.


LR6 installed in kitchen 2010. Note that all of the units appear to be of the same neutral color and uniform to one another. The color from the fixtures initially was quite nice, even though the brightness was always objectionable.

It became quite obvious that Cree chose to design this product to excel in efficacy, at the cost of aesthetic appearance and visual performance. Over the years they have made excuses for this by stating it was their intent to produce high angle brightness to “fill” rooms with light. This is the old “Volumetric Lighting” dodge that others have used (Acutity uses this term now) as an excuse for  the appearance of brightness in diffused optics, stating it removes the cave effect and improves visual brightness in a space. I’m not a proponent of this, nor do I agree with its basic logic. Visual brightness is uncomfortable, reduces visual performance, and creates a sense of institutional aesthetics to space. I see no reason to use high angle brightness throughout a space to light the perimeter walls, which is what is proposed in the volumetric argument. If you want the walls lighted, then use wall washers or perimeter wall lighting. In the rest of the space, brightness above 45 degrees must be controlled to reduce glare and veiling reflections on work surfaces and displays. The argument that this is no longer necessary due to the anti-reflective nature of modern displays is simply a marketing game of distraction. Veiling reflections can appear on any surface, including smart phones, magazine pages, desk surfaces, even ink on mate paper. There is no case to be made for accepting high angle brightness, period. Volumetric lighting is a sham that should be called out for what it is – lazy design targeted at achieving high efficacy (fixture efficiency) by eliminating proper optical and brightness control features that negatively impact total lumen output.

In an effort to reduce the offensive brightness of the LR6, I created a simple plastic ring trim for the LR6, which was presented in the 52 in 52 project back in 2010. It helped, but was a band-aide job to be honest.

That all said, I have recommended the LR6 retrofits to others over the years, specifically in commercial applications where the brightness issues would be less irritating or problematic. They work well in commercial truck-stop restrooms, and the local Walmart toilet, for example. I’ve also seen them in retail dressing rooms, with some success, and a couple of gift shops in hotels, as well as a few hospitality applications. Some look fine, and the product well suited, others have been awful. That’s the nature of products sold to save energy first – at all costs.

Now to the Fail
This leads to the next installation of the LR6 saga. After less than 2,000 hours of on-time, I noticed s decided shift in color of two of four units. One shifted to pink, the other to green. The remaining two remained steady and neutral. This condition worsened so quickly that it appeared to happen day-by day. Considering how little these fixtures were used, the change and rate of shift was somewhat alarming.


LR6 in Kitchen 2014. Note shift to green and pink in 2 of 4 units after just 2000 hours in service.

Now, anticipating there will be an argument made that the plastic glare shields I added have caused the issue, I tested the fixtures with and without the shields at 4 points within the fixture, including one at an LED in the array center using thermal probes, and found no difference with or without them, so am certain these had nothing to do with this issue.

Note also that the difference in image color is due to two factors. First, the original image was taken during the day (see the window), so there was a fair amount of daylight added to the space. Second, the camera used to take the first image has long been replaced. The second image was taken with the camera in my Samsung Note 3. This changes nothing in regard to the results being shown. The green and pink shift issue is very real. In testing the color performance of these fixtures, from the baseline of 2700K when new, the neutral fixtures were now 2750, the pink ranges from 2249 to 2399 depending on how long it is left on, the green is stable, but at 3350. The neutral fixtures were now 95CRI (92 CRIe / 94CQS), the pink 91CRI (90CRIe / 91CQS), and the green 87CRI (81CRIe / 89CQS), while the Du’v’ was as expected – the neutral was +.001 (anything under .002 is acceptable, the pink  -.0045 to -.0061, and green +.008, which, combined with the CCT shift, explains the movement from neutral to green and pink hues. In other words, the difference in color was not just subjective, it was measurable and significant, with the two shifted products falling well outside the ANSI bin standard for the 2700K CCT baseline. It was also interesting to note that after the neutral units had also shifted cooler, indicating they were likely on their way toward similar failure as the other obvious pair.  This was a disappointing outcome from a $275 investment and completely reverses my impression of this product from exceptional to unsatisfactory.

The shift from the black body line tells the whole story with the pink and green movement clearly visible.

The shift from the black body line tells the whole story with the pink and green movement clearly visible.


Overlay of the three colors shows how the original white light characteristic (the green line) is shifted both up and down to produce the pink variation (yellow line) and the green (red line).

The differences between the outputs is also clearly visible when compared against the 2700K standard center for the McAdams Ellipse, showing a variation well outside 3 steps, making it clearly, objectively verifiable as being a visible difference.

The differences between the outputs is also clearly visible when compared against the 2700K standard center to the McAdam ellipses, showing a variation well outside 3 steps, making it clearly, objectively verifiable as being a visible difference.

The Fix is In
Rather than replace these products with the newest version of the same – which to me has the same glare and brightness issue – regardless of the new lower price, I decided in stead to remove them and replace them with a more conventional PAR20 retrofit lamp from Philips. This allowed me to re-install the baffles in the downlights to create a proper appearance to the fixtures. I chose this as an opportunity to install new nickel silver baffles to fit the metalwork in the kitchen. The new lamps use 8W, instead of the 13W of the LR6, cost only $14, and produce more light on the surfaces I care about – the counter tops. Better still, the glare bombs are gone. While the end product efficacy is a bit lower due to the baffle absorbing some of the light, I just don’t care. I can now use the overhead lighting again. Hazah!

New Philips PAR20 LED lamps in new nickle baffles ends the glare, reduces offending brightness and reduced energy consumption by 45% - and eliminated the color shift issue.

New Philips PAR20 LED lamps installed with new nickel baffles ends the glare and offending brightness while reduced energy consumption by 45% – and eliminated the color shift issue.

Still Not Perfect
One issue remains, however. Dimming of the new “Dimmable” retrofit lamps remains pathetic. The new lamps only dim to about 50% of full brightness, using the newest Lutron wall box dimmer designed for dimming LED/CFL retrofit style products. However, at least don’t flicker while doing that, so I’ll live with it. The reduction in fixture brightness, coupled with dimming to whatever level they can deliver is a big improvement in both visual comfort and overall appearance in the space. Concerned that we were placing these lamps in a downlight, when the label for the product specifically states “not for fully enclosed fixtures” I checked operating temperatures and found that in the large, ventilated 6″ recessed can in an un-insulated space, their was no indication these lamps are under any stress. I am also not a fan of 2700K LED color, as it tends to look a bit artificially yellow-orange, but it is what it is.

Still Not a Fan of the Retrofit After all these Years
I remain solidly against retrofit solutions, as I believe they present compromises in performance and appearance, and apparently in reliability. Yes, I recognize it is the cheapest and easiest solution to deploying LED technology and saving energy. So are adding dimmers and automatic lighting controls, often for a lot less money.  While we spin our collective wheels selling ourselves short with cheap fixes, the actual potential and performance liabilities create reputation issues for the technology that will take years to overcome. The CFL died a PR death more than a technical death, LED retrofit products have the same potential for harm to the ultimate goal of integrating LEDs into the mainstream.

I’ve been using this kitchen as a test bed for applying retrofit solutions in a typical down-light condition. This is the last time we will apply this approach, as I am still unsatisfied that this is the best looking, or best performing solution. Now that down-lights can be found for under $100, with proper optics and external, truly dimmable drivers, my next round will be to do what I know to be the best solution – replace the fixtures completely and be done with it. For the meantime, I can now at least enjoy the kitchen lighting again.


For anyone interested in saying hello in person, to knock ideas around, or just tell me what you think of things, meeting up at a conference is ideal. Since I try to bring original content to each venue, the time it takes to put a presentation together is enough that I usually limit the number of presentations to 3-5 a year. This year is about over, but I do have 3 more to go on the schedule, for anyone interested.

The next outing is the LED Show, which is usually held in Las Vegas, but will be at the Los Angeles Convention Center this year. I’ll be there in the afternoon of the 17th, the morning of the 18th, and for a short time after the presentation session on the 18th. I’ve been presenting at this show for several years, and always have a good, meet new people, and learn a few things. Hope to see you there.

This is the presentation brief for the LED Show, Thursday September 18

This is the presentation brief for the LED Show, Thursday September 18

The next presentation is for members of the Chicago Lighting Club, I’ll be presenting the evening of October 20th. The topic is going to be held back as a surprise and fun for the designer types out there.

Directly following the Chicago Lighting Club I will be presenting at the LED Specifier Summit in Chicago. This is a great program and the one day format makes it perfect for busy designers to get in and out. Chicago is closer to home than most venues, so if you are in our neck of the woods, stop in and say hello.

Spec sum

I will be presenting at 2:00PM in Ballroom E

I don’t have any further planned public events on the calendar for the remainder of 2014. I do have presentations prepared on various topics for private presentations, both on a consulting basis, and for use in training sales, marketing, and design members about lighting, the lighting market, and solid state/LED technology on a practical level. If you have something in mind, let me know, we can create custom content as well.

In a recent article published in Architectural SSL on the topic of blue light content of LEDs, I attempted to present the discussion of blue light from the perspective of those raising concerns about blue light hazards against known and practical objective knowledge on the topic. The article covered the gambit of concerns, from retinal damage concerns to melatonin levels in occupants, from both sides of the argument, as there are those who dismiss this as a non-issue out of hand. The article also forwarded two conclusive suggestions. First: The research on this specific topic, as it relates specifically to LED light sources, is a little thin. Second: For those concerned about blue light content, selecting LEDs of a lower CCT and higher CRI delivered the lowest blue light content. Whether or not this is the best choice for visual acuity was not the subject of the article, nor was it suggested as the best solution overall. There is a great deal of research supporting the concept of high CCT light for enhancing human visual performance. Much of this was completed under light sources other than LEDs, so there is no caveat included that states anywhere that blue light content of LEDs is at acceptable levels, or of no concern.

On the topic of blue light, the conversation will invariably include a mention of the fact that human kind evolved under daylight, which contains blue light, thus, there is no issue with blue light to be concerned with. That argument is nonsense of course. We also grew up under some amount of UV light as well, yet we know for a fact that this is dangerous to both our skin and eyes. When we added sunglasses to the formula to cut light to the retina, which then causes the pupil to dilate to accept more light, we soon discovered that our low grade sun shades were not filtering UV light to the same degree as visible light, which created an explosion in retina cancers and other UV related physical damages we now know to control. This is why virtually all sunglasses sold today now include specific UV filters to control damaging rays, and why we humans, evolved under the sun, wear sunblock to protect ourselves. We also live under a lot if infrared radiation, but are hardly going to be sticking our faces in the fire claiming our eyes are safe, since that IR radiation has been around since we emerged as a species. The reality is, artificial light is just that, artificial. It is not natural light, no matter how we market it. This artificial creation of light is similar to our fatty foods. The balance between what is a natural blend of fats, proteins and carbohydrates is manipulated to achieve some result that is not the same as cutting a raw slab of meat from a living animal and eating it, or simply consuming a raw unprepared vegetable. Just as we have taken what naturally nourished us in raw foods that now cause us disease, artificial light can and does contain similar liabilities. This has been the case long before LEDs, and is still with us in the solid-state age.

The IES has issued an interesting document on the topic of higher CCT light sources as a more effective approach to efficient visual performance. This is TM-24-13 ‘Adjusting the Recommended Illuminance for Visually Demanding Teasks Within IES Illuminance Categories P through Y Based on Light Source Spectrum’ (a ridiculous document name BTW), is frequently quoted by those supporting a very high CCT light source be used to enhance visual performance. However, this is not the core data point TM-24 uses to establish light source choice at all. The metric used is the S/P ratio, or Scotopic/Photopic ratio, which indicates how the spectral power of a light source supports the full range of Mesopic vision. In this document, typical sources are cited as examples, based on common lamps and light sources, from HPS to Daylight, with a relative S/P ratio for each. None of these sources were LEDs, nor was the discussion of blue light content included in the EVE (Equivalent Visual Effect) summary. There is no suggestion, positive or negative, that LEDs of any CCT support the relative EVE or S/P ratios based solely on the CCT they produce. Further, there is nothing in the document suggesting that the characteristics of LEDs will enhance or detract from the evaluations, because, simply, LED light sources were not addressed at all. The only solid conclusion one can make from this document is that a high S/P ratio is a significant factor in optimizing visual acuity. While with today’s available light sources, and using daylight as the supposed “perfect model”, it might be suggested that high CCT sources alone are the solution, this would be an overly broad, overly generalized and simplistic interpretation of the content of TM-24.

Now, that set out, let’s look into another topic I believe is being slipped by without proper scrutiny. This is the idea of modifying human biophysical responses to light by purposely introducing a light spectral power distribution to attain a desired result. Specifically I am talking about the known effect of blue light in the range of between 430 and 460nm that imparts a melatonin suppression response, with a circadian efficiency peak of 485nm+/-. It is suggested that if we purposefully manipulate and add (or allow to exist) blue light at these wavelengths, we will help people feel less drowsy and more energetic. I believe this broaches an area of ethics we as a community need to fully resolve before we accept this as a desired effect and forge ahead with high CCT light sources, believing we are reaping the benefits of better visual performance with a pep-pill bonus. We all know that adding stimulants to drinking water could reduce drowsiness in working environments. This is, of course, unethical (not to mention illegal), so we don’t do it. So, is purposefully manipulating circadian rhythms of offices and manufacturing facility employees, using light that is specifically and purposefully, in full knowledge and intent, doped to reduce melatonin levels to increase alertness? Do we know for a fact, or even beyond a reasonable doubt, that this has no long term health effects? I suggest that this is not an ethical approach to lighting, and that any attempt to purposefully amp up alertness by doping the lighting system with increased blue light without the consent and knowledge of the occupants, raises serious questions that are well beyond the realm of marketers and proponents of high CCT/high Blue light products.

This leads to the oft-cited suggestion that LEDs produce no more blue light than any other light source, thus are of no concern. The DOE has even supported this position in statements, effectively dismissing any discussion of the topic as irrelevant. What’s missing, and of critical importance, is that this generality is simply incorrect. While there are some LED sources that deliver no more blue light than other conventional sources, does this mean that the sources held up for comparison are acceptable as a baseline? How do they align with the vaunted perfect light source, daylight, and is there a way to attain what we want from light sources without the increased blue light content? In the sweeping, overly broad statements made, none of these questions are addressed, only avoided.

At various times I have suggested that high CRI LEDs of any CCT, produce less blue light as a portion of total light energy, than low CRI LEDs. This is based on LED light sources founded on the effect of phosphor conversion of either a 405nm violet, or a 456nm blue die light source. Since we are talking about blue light, as defined by melatonin suppression (430 and 460nm) the more of the core blue light of the LED that escapes, the greater the blue light presence will be. To increase CRI of an LED, more blue light needs to be down converted to the yellow-green and red wavelengths, leaving less escaping as raw blue light. Thus, the higher the CRI, and a subsequent lower blue light content as a portion of total light energy. As you will see here, this theory has its limits.

So, with this all in mind, I did a few tests of light sources to see just where we are with the blue light content issue between sources. I captured spectral data in micro-Watts per square centimeter using a Mightex CCD Spectrometer, then normalized all sources to an identical total output in watts of irradiance between 400 and 700nm, where we do most of our seeing. Withing that total output, I isolated the energy produced between 430 and 460 (>430 to <460) to see how much of the total energy produced by the source landed in the blue light zone being discussed. Here are the results:

While most spectral data comparing products shows relative distribution, its not until actual irradiance is compared that the differences between sources is revealed. In this case, all of the sources are generating the same exact total irradiance in microwatts per square centimeter, so the differences in balance between produced wavelength energies is made apparent.

While most spectral data comparing products shows relative distribution, its not until actual irradiance is compared that the differences between sources is revealed. In this case, all of the sources are generating the same exact total irradiance in microwatts per square centimeter, so the differences in balance between produced wavelength energies is made apparent. Note the red spike for the 2800K LED, which generates its high CRI rating, comes from an added red LED die in the array, not phosphor conversion.

  • 5800 K Daylight (cloudy sky)  = 98.9 CRI – 9.6% of total light energy falls between 430 and 460nm
  • 5000K Daylight (direct sun) = 99 CRI – 8.4% falls between 430 and 460nm
  • 5800K LED @ 65 CRI – 20.8% falls between 430 and 460nm
  • 5000K LED @ 90CRI – 13.1% falls between 430 and 460nm
  • 4000K LED @ 80CRI – 11.2% falls between 430 and 460nm
  • 4000K D841 T8 Fluorescent Lamp – 12.2% falls between 430 and 460nm
  • 2800K LED @92% – 6.8% falls between 430 and 460nm
  • 2500K Halogen @99.7 CRI – 2.2% falls between 430 and 460nm
While the graphic looks like a jumble, looking at it carefully reveals the ramp from lower left to upper right of halogen, the distinctive blue pump hump of the LEDs, the flatter total coverage of daylight, and the strange tri-phosphor spikes of the fluorescent source.

While the graphic looks like a jumble, looking at it carefully reveals the ramp from lower left to upper right of halogen, the distinctive blue pump hump of the LEDs, the flatter total coverage of daylight, and the strange tri-phosphor spikes of the fluorescent source. Note: In these graphics, I have reverted to relative spectral data.

The products tested ranged over and under the black body line, which is apparent when comparing them side-by-side as some yellow green, some magenta.

The products tested ranged over and under the black body line, which is apparent when comparing them side-by-side as some yellow green, some magenta. To make matters even more interesting, the poor CRI 5800K and 4000K T8 lamp came closest to sitting on the black body line, even beating daylight, while not matching its CRI (or CQS). This indicates flaws in our modeling, including and beyond CRI itself.

So much for the LED not producing more blue light myth, and the disconnect between CRI and blue light discussion. In LEDs, not only is color quality a measure of a sources visual appearance, it can be corollary to the amount of blue light one can expect to be emitted from the light sources as well – although, as I will demonstrate, this is not always true either. In other words, we must stop assuming that all CCTs generate the same amount of blue light, or that CCT alone is a meaningful single metric in determining blue light content.

Please note that all white light will deliver blue light above the described 460nm through the peak circadian efficiency peak of 485nm. This is necessary to realize any full white appearance. However, that fact does not diminish the impact of addition blue light presence below this peak, as the circadian response curve is quite broad, ranging from <380nm through 625nm.

If we use a 9% of total energy as a baseline of acceptable blue light balance in the spectral power distribution of light sources, the following conclusions can be drawn:

  • A low CRI 5800K LED produces 2.3 times the blue light as daylight
  • A 90CRI 5000K LED produces 45% more blue light than daylight, but 48% less than the lower CRI/Higher CCT LED
  • The high CRI 5000K LED generates no more blue light than an 80CRI 4000K LED or T8 fluorescent
  • The 2800K 92 CRI LED generates 25% less blue light than daylight
  • The 2500K 99CRI halogen lamp generates 75% less light than daylight

This is, by no means an endorsement of reverting to halogen light sources or call to abandon the pursuit of LEDs or high CCT light sources. What I am suggesting is that we be realistic and recognize what we are working with, and if it is possible to realize both high CCT s and high color performance, while controlling blue light content, perhaps we should. The 5000K LED at 90CRI is one example of this, we gain the higher 5000K CCT over the 4000K, with greater color accuracy, while suffering no gain in blue light. The next question is whether this is corollary to the important S/P ratio. For that, I re-measured each of the sources using the Asensetek Spectrometer to create a side-by-side comparison as it would be applied using the principles described in TM-24-13. Here are those results:

  •  5800K Daylight – S/P Ratio 2.41
  • 5800K / 65CRI LED –  S/P ratio 1.83 (does not measure within TM-24 table showing 2.0+)
  • 5000K /90CRI LED – S/P ratio 1.61 (does not measure within TM-24 table showing 1.85-2.05)
  • 4000K / 80CRI LED – S/P ratio 1.36 (does not measure within TM-24 table showing 1.6-1.8)
  • 4000K / 80 CRI T8 – S/P ratio 1.59 (at bottom of TM-24 table showing 1.6-1.8)
  • 2800K / 92CRI LED – S/P ratio 1.36 (within TM-24 table)
  • 2500K Halogen – S/P ratio 1.24 (within TM-24 table)

Not what I expected, and more than a little dissapointing. It appears that LEDs are not delivering the same S/P ratio performance as the fluorescent sources cited in the TM-24 recommendations, or the daylight and fluorescent equivalents of the same or similar CCT. Apparently more work is required here. All of the LED sources, regardless of CRI or CCT, are falling short, which indicates they will not perform better than their fluorescent counterparts. Even when the 4000K LED and T8 lamp are compared in my little test, the LED fell short. Additionally, while I personally hoped to see a connection between the CRI and the S/P ratio, this was not to be. Quite the opposite. The high CCT, low CRI 5800K LED topped the charts in regard to the S/P ratio (of the sources tested thus far anyway) while also delivering poor color performance and the greatest amount of blue light. This indicates to me there is a serious flaw in the way all of this is being evaluated that needs to be resolved. Otherwise, TM-24 S/P recommendations become antithetic to color quality, which is not an attractive prospect.

In an effort to understand this a bit more, I decided to make my own LED recipe using some remote phosphor plates and a 456nm blue array I had lying around – to see if I could mix up a very high CCT source with good CRI, yet avoid the blue light content. Here is the result:


This the CIE diagram of the two farbicated LED samples. Note how far south of the blackbody line they fall, looking a little magenta. Also, illustrates the issues with CRI, as these two did well there. CQS calculated to just 80. However, even it has no data to show how far these were off being white.

7000 and 8700 CCT LED Fabricated from Blue pump and phosphor discs

7000 and 8700 CCT LED Fabricated from Blue pump and phosphor discs

  • Fabricated 7000K LED delivered 91CRI – 22.3% falls between 430 and 460nm – S/P ratio of 2.3
  • Fabricated 8700K LED delivered 90CRI – 24.3% falls between 430 and 460nm – S/P ratio of 2.5 (spot on to the sky reference and 8000K fluorescent reference in TM-24

I was encouraged that a 7000 and 8700 CCT LED system could be made to generate 90+ CRI. Unfortunately all this did was demonstrate how poor CRI calculations are in this region, as the CQS values for these were a solid 10 points lower, while their position well below the black body line reflects their somewhat purplish presence. As a minimum, we should be given a Du’v’ value for all color ratings – but that is another topic altogether. Although, while the color looked off, it did a fair job of looking white on reflected surfaces and did render colors on my color checker nicely enough. The S/P ratio certainly looked good, nearing daylight and better than any of the other LEDs I tested before. So, at the least we can conclude that a high color rendering accuracy does not harm attaining a high S/P ratio.

The blue light evaluation produced decidedly disappointing results, delivering the highest of all sources tested so far. Obviously, a high CCT/high CRI (CQS) with high S/P ratio can be achieved while still deliver very high blue light content. So my high CRI to low blue light content argument falls apart as the CCT increases.

It also appears that there is a missing piece to this puzzle – since I can nearly duplicate daylight performance in both CCT, CRI, and S/P ratio, but deliver nearly 3 times the amount of blue light in balance compared to natural light. That means these artificial light sources have 3 times the impact on melatonin suppression than natural daylight. I do not find that a desirable result, nor should anyone else. I am not even considering or suggesting that there is any health impact other than potential sleep/wake cycle effects. While there is some research indicating blue light near the 400nm through 450nm range can cause retinal damage, there are at least as many papers indicating that retinal illuminance levels are unlikely to be high enough to be a concern. So, we’ll leave that topic for others or another time. My concern is that application of LEDs everywhere, coupled with the advantages of increased CCTs in visual performance to reduce illumination levels (to trim energy use)  means we are going to be exposing ourselves to a significant increases in spectral energies that effect our melatonin levels. Dismissing this out of hand seems reckless. As an insomniac, the prospects are not attractive at all.

The heart of the blue light issue as it relates to melatonin, is the use of the 456nm blue LED. Move to a 405nm violet LED, and the majority of the energy from the core LED falls outside the range of concern. However, being closer to UV light energy brings with it its own baggage that will need to be addressed, while most 405nm LEDs fall short of the lofty efficacy we see with 456nm products. Further, my experience with conventionally made 400nm to 405nm LEDs is they are significantly more sensitive to temperature, aggravating getting the most of them. Perhaps there is a solution in GaN on GaN architecture that resolves that issue.

Overall, if we agree that the goal is to achieve optimal visual performance, as shown in TM-24-13 – through increased CCTs to some degree, while seeking a high S/P ratio, we need to discover a way to maintain good color quality and accuracy (which begs a new standard, as the CRI is obviously not helping us here), while also managing the blue light content. It seems to me, after looking at these results, that all that blue light escaping is lost efficiency in delivering high color performance and creating even better S/P ratios for visual acuity. However, I was unable to achieve the desired result on my admittedly make-shift work bench.

So, to the origins of this discussion. While I have suggested that for those most concerned about blue light, the only real approach using LEDs available on the market today is to select lower CCTs with high CRI/CQS scores. These products use up more of the blue light to create the yellow-green and red colors necessary to achieve the higher color accuracy results. This was consistent with the test results presented here. When you get beyond 5000K, all bets are off, no matter what CRI/CQS rating the source achieves. This is especially true for spaces where high precision lighting is not the task in hand, and where relaxation before heading to bed is in order, the 2800 93CRI LED tested generates less blue, melatonin suppressing light than daylight. However, it does generate 3 times that of halogen, so there may be a case made for bedside lighting remaining conventional, or consider a light source like Soraa’s LEDs, which use 405nm LEDs as their blue pump, which is below the threshold of concern.

For high precision task lighting, the blue light issue is harder to avoid. To get the high S/P ratio means higher CCTs, often much higher than what many of us are accustomed to. While this can be done with high CRI (which does reduce blue content to some degree), it is not necessarily corollary, while most high CCT LEDs are poor in color accuracy (and very high blue content). Couple this to the fact that these applications also include use of higher illuminance levels, compounding exposure as a whole. There is also a failure in the S/P and CRI/CQS metrics when we get beyond 4000K, indicating a more careful evaluation is necessary to make solid decisions. Assuming a high CCT and high S/P ratio is the whole story is obviously inaccurate. Further, with blue light energies – as a component of total light energy – exceeding what we experience under daylight by as much as a factor of 3 (much more if you consider low CRI LEDs with much higher blue content), being cautious and conscious of the effect this might have on sleep patterns is a prudent measure. We might keep in mind that workers in construction, precision shooters, and others exposed to daylight on a daily basis have found blue light filtering glasses to be an aide to both visual acuity and comfort. Under the same CCT of LED light, there is an even greater component of blue to be considered. Whether or not this is going to be an issue, we do not yet fully understand. Whether the benefits of the higher CCT S/P ratio are negated by the high blue light content of LEDs is something else that will need to be studied and resolved.

I suggest that as time passes and LED technology develops, much of the blue light issue will fade as a combination of growth in understanding and increased conversion efficiency where that energy is used to generate improved color qualities – rather than simply allowed to escape, assuming some attention is paid to the issues raised here. In the meantime, avoiding simplistic assumptions, either for or against blue light, CCT levels, CRI/CQS accuracy, and S/P ratios and their meaning, is the first step in breaking through to greater results. Moving toward lowering blue light, raising CCT, establishing a new color accuracy metric, and establishing a metric for clearly indicating and defining the effect of spectral power on human visual and non-visual response also appear to be in order in the long term.

After reviewing a range of different metering choices in actual use, I compiled a summary of findings, as well as my own personal subjective ratings of features and overall utility as a lighting professional. This chart is the collection of all findings in a simple comparison table for those who find this useful (like me):

The Meter Comparison Table in .pdf format.

Note that all of the meters tested were shown to deliver accurate results when testing LED products, as well as conventional lamps. This is not always the case. Many older meters do poorly under LED light sources, either delivering unreliable results, or unstable readings. One example of this are the obsolete Minolta meters manufacturer before LEDs had entered the market. These often deliver CCT results that are far enough off more current meters as to render them essentially useless. Also, some LED products flicker at a frequency that creates moving readings, which never stabilize enough to be readable. The meters I have that exhibit this behavior were excluded from review completely, for obvious reasons.

This is by no means a comprehensive review of all the meters available to designers and engineers. I could have scoured web sites and pulled down more data to include objectively from indirect information. However, that was not my intention, and like the results I get from testing actual products against published data, there is no substitute for directly using and testing any product. The problem for most of us is that testing every option before buying is just not possible, or practical. So, with that in mind, and reflecting the fact that I have both collected more than my share of instruments and put them to use, and have had access to others purchased for and with customers, I offer the reviews as they stand. In this, simply regurgitating what I get from web sites would only pollute the results, as anyone can do that, as that is how I came to purchase those products I have, for both good and bad results. I hope that this this is of value to those making your own decisions, hoping to avoid some of the redundant purchasing decisions I have, that has led to having this many meters collected to review.

That all said, if anyone has a meter they feel was unfairly excluded here, that would like to be added, I offer this. Send me the meter and give me a few weeks time to play with it, and put it to use in tests we are completing on a regular basis. This includes whatever software is required to create a complete picture of the product in actual use. I’ll add what I find to the meter reviews by adding an entry for the specific product, and update the summary comparison table before returning the meter – unless I find I can’t live without it and find myself compelled to add to my collection – which we can discuss at the time.

This is the Lighting Passport Flagship set. Includes case and accessories in a neat package.

This is the Lighting Passport Flagship set. Includes case and accessories in a neat package.

I first saw this device at Light+Build Frankfurt last fall. I was impressed enough to find one added to my collection of tools. The Asensetek Lighting Passport is a unique product in several ways. First, it is essentially a meter head (where the cost is), coupled to an iOS or Android device that does all the computational and display work. The lighting head has a nifty slide action receptor cover, so there is nothing to come off or get lost in a bag or pocket. The measurement range is as broad as any of the other spectrometers tested here, plus some. Not only does it produce the expected spectral power distribution, CRI, CCT, CIE 1931 and 1976 coordinates and illumunance in lux and Fc, it also delivers CQS values. There are several additional data points worth singling out:

  • Du’v’ value. This is the missing piece of the CRI value we have always needed and were never provided. This tells you whether the light source is above or below the black body line. A positive value indicates the source will appear on the yellow/green side, while a negative indicates a tint of magenta will be present. When you put two sources side-by-side of the same CCT and CRI/CQS, you will see these differences clearly. Now, with the Du’v’ value, the difference will be quantified and usable in future comparisons when you don’t have both sources in the same room at the same time.
  • S/P (Scotopic/Photopic) value. This is the value that will drive future lighting decision making. This indicates how well a spectral power distribution satisfies both the scotopic and photopic visual response curves of the human eye, which combine to deliver mesopic vision, and is the center of most current thinking in explaining why we find one source more visually stimulating and clear over another. This is also the value described by the IES in TM-24 13, where the application of S/P ratios can be used to reduce energy use, by taking advantage of the dynamic advantage of high S/P ratio light sources ability to generate increased visual acuity at reduced illuminance levels.
  • PPFD, or Photosynthetic Photon Flux Density. This is the amount of light in umol/sec meter sq. in the spectral distribution (red and blue peaks over human vision in yellow green) that is used in lighting of plants. While not everyone will find this useful, when you need the data, this meter delivers it. Its also an interesting value when looking at how an artificial source and daylight compare, but that’s for another discussion.
  • FWHM color value. This is an interesting value that shows the width of a products light output to 50% of its relative power in wavelength. This is an indicator of how broad the total power distribution is, and is very interesting when comparing two sources to one another.
  • Peak and Dominant wavelength. Peak wavelength tells you where the highest output of a product is centered (in color), while dominant wavelenght tells you where it sits in CIE coordinate positions.
  • ANSI bin and CIE McAdam Ellipse values. Based on a preset standard value for the CCT a source is nearest, you can see where the measured product sits within the standard ANSI color bin, and how far off in McAdam steps it is from the CCT standard center. These are excellent tools in comparing two sources to one another of the same CCT and CRI, and along with the Du’v’ value will provide insight into what to expect in application of the products, in relation to color differences between two products.
  • Multiple source comparisons and multiple readings of a single source. The Lighting Passport allows multiple readings to be taken and compared, or collected into database. This provides direct comparisons on the meter itself of two products to one another, or of multiple readings taken in sequence within one test session. This not only allows comparisons to be made objectively on all metrics, it provides a tool for evaluating color shift over light distribution patterns. For my own use, using this meter on a goneometer rig means I can not only collect the illuminance data necessary to define light distribution, but see how the color values shift throughout that light pattern.
  • Light transmission accessory software. This small utility program is great for evaluating light transmission of materials, generating a simple report of the materials properties in both total transmission, and spectral transmission. This is a tool that every lighting meter used for design should have.
The range of information available to view on screen is excellent, clear and easy to read.

The range of information available to view on screen is excellent, clear and easy to read.

So, with that all covered, one would have to say that the product is impressive, and spot on target for what lighting professionals need in a portable and small lab environment. But, that would be missing some even more interesting features of the Lighting Passport that puts it head and shoulder ahead of the rest. Like this:

  • Separate metering head operated by wireless (Bluetooth) connection. The small head size means not having the meter body height involved in the placement of the sensor, which can be an issue in task illuminance readings, where the light source is inside 36″ of the target surface. In all the other meters with an integrated head, the body height of the meter gets in the way of gaining an accurate measurement. The Passport includes a small stand attachment that allows the meter to be set where you need it, then stand back to eliminate the influence of being in proximity of the measured result.
  • Works with ANY iOS device and Android 4.4.2 device, identically. That means phones, tablets and Pod music devices. So, if you already have an iOS or Android phone, you don’t need anything but the meter head, which slips into a pocket, to take for on-site measurement. This also means that use of a tablet sized device allows the meter and its output to be viewed easily by several people in a room, even projected onto a video monitor. In my case, I’ve connected the sensor head to my Samsung Note 3, and taken readings in a room with people viewing the results on an HDTV connected to the Note 3’s USB connector. This takes education sessions, product evaluation sessions, and general discussion and presentation to a level no other meter can match. Here’s another neat feature of this product – the interface software is open platform based, which means those with the need to create a custom interface for specialty evaluations have that available to them. This also means that updates to operating software through Android and iOS app outlets will make keeping the product current will be far easier than anything proprietary products can match.
Separating the meter head from the display is an outstanding feature that allows it to be used in a wide range of applications, and not interfere with readings.

Separating the meter head from the display is an outstanding feature that allows it to be used in a wide range of applications, and not interfere with readings. The little clip to the left attaches the head to any tablet device with a secure clamp feature.

The lighting head is compact and when mounted on its provided stand, stable for remote measurement. It is also the only part you have to carry with you to a job site, should you already have the software installed on a smart phone.

The lighting head is compact and when mounted on its provided stand, stable for remote measurement. It is also the only part you have to carry with you to a job site, should you already have the software installed on a smart phone.

The meter and its design is impressive enough to be a reason to consider it, and is very usable as a stand alone. However, on top of this, the Spectrum Genius software creates an expanded opportunity for evaluating all of the collected data in a single screen, and compare sources, or multiple readings at once. This adds a layer of utility to the metering system that really enhances its use for those doing a lot of work in evaluating application results or products for consideration in specification. It also generates very nice reports, exports data into spreadsheet worthy data sets for use in other calculations. In my case, I export the data set from multiple reading sessions to create photometric reports that are used in conjunction with the spectral reports to create all of the same data one gets from an LM-79 report, in-house, of any product I can get my hands on. That means I have been able to compare LM-79 reports provided by manufacturers to test results of product samples – with interesting results. I can also provide preliminary LM-79 evaluations of products in the design phase for customers, before they  are completed for final testing at an independent accredited lab. No more ugly surprises and re-testing issues when a product does not perform as needed or expected.

The Spectrum Genius software puts everything in one place, making evaluation quick and easy to see.

The Spectrum Genius software puts everything in one place, making evaluation quick and easy to see.

The Lighting Passport can be found in the market under the brand name Asensetek, and is sold in the USA by Allied Scientific Pro. The prices are wide open, you can order them on line, and with a range of between $1,500 to $2,500 for the meter and its attachments, plus software for free to $500, this package delivers a massive bang for the buck. This pricing is less than some of the high end white-light illuminance meters on the market, while delivering far more information. The product can also be calibrated, so can be used for precision applications and  other uses where it is important to have backing for the data collected.

Printing a report from the software to provide to customers or store as a record for comparisons is a nice feature

Printing a report from the software to provide to customers or store as a record for comparisons is a nice feature

In conclusion, I use the Lighting Passport as my go-to meter choice, and have found very little to complain about. It’s not perfect:

  • The software is a little glitchy in its display, but not so much that I find it an issue.
  • The software also creates a graphic error when creating a report using CQS, as it overlaps the data from R values with the Q values from Q7 thorugh Q15, which is truly annoying. I’m hoping this is resolved in future software updates.
  • The software also uses a dongle for security, which some will hate. I like it, as I have the software installed on both my laptops and desktop, and can move the dongle between them for use anywhere. others will find the tether objectionable I am sure.
  • The transfer of data from the meter to the software is through email or iTunes over wireless, although you can upload the data by file explorer in Android devices. This is fine with a smart phone, and works just fine with the iPod device provided in the Lighting Passport Flagship set (with wireless availability). It would be nice to be able to connect directly from a desktop through wireless to download stored files, but this is not a serious problem, and more an issue with the devices themselves – separate of the meter system. I find no compelling need to operate the meter from a desktop, as the remote head and hand held ergonomics of the data collecting device are just fine. In a lab space, use of an Apple mini-pad or other tablet device works quite well, and eliminates the need to have a computer dedicated to lab duty where it sits unused most of the time.
The package of components are well thought out, and well designed. Quality is very good.

The package of components are well thought out, and well designed. Quality is very good.

Overall, for anyone looking for a portable, high quality spectrometer/illuminance meter product, the Lighting Passport is going to be hard to beat. At its current price, I would say impossible to beat actually. More on this from Allied Scientific Pro More on the Spectrum Genius Software

We have now entered the modern era, where meters are available with a dazzling array of features, at a fraction of the cost once commanded. In this case, the UPRtek MK350S, available also in a lesser featured, and lower cost MK350N version, produces amazingly beautiful results with little pain in the wallet or the head from learning to use it. You may find this also sold under other brand names, such as AIBC, or sold through outlets such as Allied and Ikan. I first saw the MK350S at Light+Build in Frankfurt. A customer of mine also saw them, and was so impressed, he purchased one and has allowed me some time to play with it and in preparation of building up a test lab for his company.

MK350S package

MK350S package

The MK350S comes with all the parts necessary to put it to work. With a bit of minor assembly, insert the battery, slide in the data/wireless card, charge it up, and its ready to go. The touch screen interface is a great feature, as is having the results readily displayed on the device itself in full living color. Their is a camera function that not only allows a picture to be associated with the readings taken, but assists in aligning the sensor when readings are taken.

This meter can deliver the entire collection of desirable architectural lighting results (with a couple of interesting exceptions we will cover in a moment.) The output on the screen can be configured to show:

Spectrum view
CIE 1931 view
CIE 1976 view
LED Bin position (within a standard ANSI bin for the CCT reading)
Footcandles and Lux
Dominant and Peak wavelength
Comparison of two light sources
Associate a photo to a meter reading

The data can be stored on an SD card for use within the companies basic software, which duplicates the presentation of the device itself. Overall, the product runs in the $3,100 range at the advanced level, while the MK350N can be hunted down for around the $2,500 mark. The extra $600 produces several nice additions, particularly the lack of CRI and Purity. Further, the MK350S includes wireless communication for control of the device, where this is an add-on the the MK350N, which will bring its cost closer to the MK350S level, and still be missing the CRI function. Here is a link to a comparison of the two MK350N vs. MK350S.


The range of delivered outputs from the MK350S is impressive

I found the product an exciting tool. Its difficult to resist walking around taking readings all over the place and looking at the results. It’s great having this all in hand, without cables connected to a laptop, and a display bright enough to be seen in daylight conditions. The meter fits well in the hand, and goes a long time on a charge. Overall, this is a great new step forward in bringing accurate, relevant lighting data to specification level decision makers and evaluators.

LUX.G image from AIBC web site

LUX.G image from AIBC web site

There is another unique feature provided in the MK350S, called LUX.G that generates a colorized brightness ratio image of a space to illustrate brightness patters. This false color imagery helps the user see the brightness patterns more clearly, and is rather interesting. Not sure exactly how useful it will be, but it is certainly something to look at.

This all said, I have a few nits to pick with it.

No CQS. With CRI under attack, and likely to be replaced soon, likely with the CQS or other similar system, I wonder how they will deal with the new standard when it emerges, or will this be a matter of having to replace the product itself?

No P/S Ratio. It seems an easy addition to include the Photopic/Scotopic ration function, considering how this is becoming a topic of discussion for future approaches.

No McAdam Ellipse evaluation in the bin function. With the data existing in the system as it sits, there is no reason this comparison could not be included.

Not wild about the software/wireless registration loop. The company makes every new user jump through a few hoops to get their software up and running, and the wireless card to work. The real problem here is that the wireless card must be functional to access the memory card for storing data, so until that’s done, there is no way to get the data from the device anywhere else. But that’s okay, since the data is useless without the software, which also requires a registration loop.

Integrated display on top with fixed light sensor is not ideal. The fact that the sensor is permanently stuck in the end of the meter, and the display is on top, means that in lab or tripod mount uses, the meter must be connected to a computer to see the results. Further, the sensor at the end of the meter means reading some angles must be done blind, then read, which renders the camera assisted aiming moot. While we’re on that topic, the camera position on the head is enough offset of the sensor, that measuring close up objects is a bit odd, requiring you offset what you see to get the sensor properly centered. It would be a nicer device if the sensor head popped off for hard-to-read, tripod, and lab application.

These are all minor issues in the bigger picture, and will likely be smoothed out as the product is applied over time. This is a level of performance, and superior in the GUI over much more expensive systems, like the Minolta CL500, whose display is poor, or others where connection to a computer is necessary to come even close to what is displayed in this handheld device.

More on the MK350S from UPRTek and from AIBC

To compliment a standard light meter, which does a fine job collecting illuminance information, I sought a low cost solution to evaluation of color data, specifically CCT, spectral power distribution and CRI. My goal was to find a product under $2,000, that could be calibrated, that would deliver me color information simply and without a large amount of special technical effort. I found that in the Mightex CCD Spectrometer. At a base price under $1,700, it fit the budget nicely. Of course I added a few accessories to it, and paid them to calibrate the meter with a fiber optic mounted cosine sensor, which increased the total invoice to a touch beyond the $2,000 target… However, in the end, I found the results to be exactly what I was looking for – almost.

Mightex CCD Spectrometer

Mightex CCD Spectrometer

The CCD based (same technology as high resolution cameras) spectrometer is that it holds its precision over a wide range of temperatures and for long periods of time before requiring re-calibration. While the software is not as slick as the previously mentioned Orb Optronix SP-100, it is certainly functional, and delivers the information I wanted from it. It calculates CCT and CRI, and presents it in both graph and graphic formats. The spectrometer’s raw data can also be downloaded in a file format usable for evaluation in spreadsheet form.

Connecting the meter to a computer is as simple as plugging in the USB cable, which also provides the power to the unit. I use a fiber optic cable from a cosine correction end attachment, as this allows me to leave the box and its connection to a laptop on a table, while reaching up to ceiling products, or fixing the reception head to a holder for lab testing on the goniometer.

Mightex CCT and CRI screen output

Mightex CCT and CRI screen output

mightex graph

Mightex Graphic output

The output reports are very easy to read, and show all the information I need them to, including individual R values in the CRI calculations, and pertinent color coordinates in both numeric and graphic format. For the money, it delivers most of what much more expensive equipment provides, in a very simple to use and apply unit. The software does take a few moments to figure out. Of particular issue is selecting an appropriate sample rate, sample number, and integration time to create the most accurate CCT and CRI result. This is usually done by experimenting with various settings in the operating software until a smooth spectral distribution curve is created. A smoothing function can also be applied to improve results.

This is not going to be a user-friendly device for anyone who is not familiar with photometric testing using spectrometers. Failing to apply the proper settings creates wildly erroneous results that will be confusing to those who are not familiar with what causes them.

One missing piece that needs mentioning, is that the Mightex does not produce illuminance values in any form usable in architectural lighting. The data can be read in absolute irradiance as uW/cm2,  which can be translated and converted to other forms. I needed this exact data for one customer in the UV light curing business. However, for the most part, the data is most useful in spectral power distribution evaluation as presented without bothering with any such effort. For my uses, other meters provide me the photometric data I need without relying on the Mightex for use beyond color evaluation and performance. Overall, this is a nice tool for those looking to create a low cost lab setup. For the architect, lighting designer, or electrical engineer looking for a portable light meter solution with CCT and CRI capability, it is probably not an ideal solution.

More on Mightex Systems