Posts Tagged ‘SSL’

Follow along, and see if this sounds familiar…

In the process of designing a new light, you begin by collecting manufacturer data sheets. You rifle through the LED data to find lumen output for LEDs and select one with a rated lumen output of 390@700mA, 3000K CCT / 90CRI (test current), and 188 lumens per LED at 350mA (calculated value), @ 3.4 Vf, for 158 lumens per watt. Nice!

You calculate what you need to make the target 1000 output lumens, and design a product around the data and calculations, use 7 LEDs operated at 350mA, to include 30% over the target to compensate for optical losses and temperature per the manufacturer data sheets. Using first article parts to build a prototype, you send it off to the photometric lab, expecting to see results very close to what you calculated. You can live with a minimum of 900 lumens, but hope to see better than 1000, as the data provided by the component providers indicates this should be the case.

Your expectations are based on the following:

  • The LED data sheet says the LEDs can produce 188 lumens at 50mA
  • 188 lumens x 7 LEDs = 1316 lumens, providing 30% more than the desired end result
  • The optical data sheet claims an efficiency of 92% (8% loss)
  • The driver data sheet shows 97% efficiency at 350mA / at a voltage range of 18 to 34Vf, with a rating of 12W (covering the string voltage of 23.8 Vf – with a calculated watts load of 9.8W)
  • CCT selected is 3000K by LED data sheet, 90 CRI
  • Your LED case temperature tested at 40°C after 20 minutes, which the manufacturer data sheet shows minimal lumen loss, well within expectations and over-design of 1504 lumens.
  • Calculated and expected results >1000 lumens, 9.8W, 102 lm/W.

The results you are expecting

  • Luminaire total lumens 1100+
  • Watts with driver loss 10 +/-
  • Lm/W = 108+
  • CCT = 3000 / CRI = >90

The lab results come in, and you anxiously open the file and discover the following:

  • Luminaire total lumens 620.6
  • Watts load 8.7
  • Lm/W = 71
  • CCT = 2850 / CRI = 88.5
  • Measured LED case temperature 66°C
  • LED ambient temperature under the optic is 40°C
What happened?

There are numerous variables that come into play that will trim effective luminaire output from expectations built around manufacturer data sheets. Here are a few that this example will have suffered from:

  1. CCT is a generalized term. Actual LED CCT’s vary. Further, optical systems can impart a warming of LED color by as much as 200CCT. Operating LEDs at reduced current will also cause warming of CCT.
  2. CRI is an averaged value, and will vary somewhat by LED bin or production run.
  3. The actual LED lumens from purchased reals of product produce 167.32 lumens at 25°C Tj – a loss of 11% based on bin group purchased.
  4. The LED manufacturer data is based on tests of cherry picked LEDs strictly held to a Tj of 25°C, in an ambient temperature of 25°C, for a duration of 20 milliseconds – The actual LED case temperature of the LEDs was 66°C, with an ambient of 40°C, resulting in a junction temperature of 77°C – Result is a de-rated LED output of -15%.
  5. The LED manufacturer data is based on tests of LEDs that have never been populated onto a board, so have not experienced the thermal cycling processes involved there. One thermal cycle reduces the measured LED output by 7%.
  6. The driver manufacturer data assumes an ambient temperature of 25°C, operation at exactly 120VAC, operating at the maximum Vf. – Actual driver operating conditions are 42°C ambient – resulting in an efficiency loss of 3%
  7. The actual driver output is not 350mA, it is actually 340.4 mA, which is within the +/- 5% tolerance, for a current and LED lumen loss of 3%.
  8. The actual LED string voltage measures 22.4, indicating the LED Vf is 3.2, not 3.4 as shown on the data sheet – for a loss of 6% energy through the LEDs reducing lumen output
  9. The driver actually delivers 21.97Vf when connected to an LED string presenting a voltage drop of 22.4Vf while maintaining the output of 340.4mA, for a loss of LED lumens of 2%.
  10. The driver efficiency rating of 97% is at full load. The load connected in the design is 62%, resulting in a measured actual efficiency of 89%.
  11. The optic used has a measured efficiency of 97%, but that is based on simulated data derived from the manufacturers design software. Actual optical efficiency measures 88%, for a loss of 9%.

Add this all up and you get:

  • Lumen loss from actual LED lumens vs. manufacturer data = 33% (188 x .67 = 125.96)
  • Lumen loss from thermal conditions at the LED from manufacturer data sheet to actual applied conditions = 15% (125.96 x .85 = 107.066)
  • Lumen loss from driver under-current / under-voltage conditions = 9% (107.066 x .91 = 97.43)
  • Lumen loss due to actual optical efficiency = 9% (97.43 x .91 = 88.661)
  • Loss of driver efficiency due to ambient condition = 3% (.97 x .97 = .949)
  • Loss of driver efficiency due to low load condition = 8% (.949 x .92 = .873)

Total actual lumens per LED = 88.661
Total luminaire lumens = 620.63
Actual driver LED load = 7.625
Total driver efficiency at actual load = .873
Actual driver watts at 120VAC = 8.733
System lumens per watt = 71.07 lm/W

 What now?

The next step is to adjust current to the LEDs to push output up to 500mA, and get the following:

Total actual lumens per LED = 120.243
Total luminaire lumens = 841.70
Actual driver LED load = 10.9
Total driver efficiency at actual load = .903
Actual driver watts at 120VAC = 12.07
System lumens per watt = 69.73 lm/W

Now what?

The following is what happened:

  • The higher current increased LED output, but increased heat as well, so lumen increase was less than the increase in current supplied. The result is less than expected output increase and lower efficacy.

So, you push the LED to its maximum test current of 700mA and get:

Total actual lumens per LED = 159.59
Total luminaire lumens = 1117.13
Actual driver LED load = 16.3
Total driver efficiency at actual load = .88
Actual driver watts at 120VAC = 18.53
System lumens per watt = 60.28 lm/W

Now what happened?
  • More current increased heat even more, in both LED points and ambient inside the luminaire
  • The higher current increased the driver LED load beyond the original driver selected, requiring a change from a 12W capacity driver to an 18W capacity, which has a lower efficiency when loaded at 16.3W.
  • The composite of heat and driver selection compounded to reduce efficacy, but increased lumen output to exceed the design target.
The solution?

There are several:

  1. Lower expectations. The original target is obviously pushing the limits of the LED configuration selected. There is no solution to resolving the difference between manufacturer data and actual performance, this is simply the reality of this technology.
  2. Search for higher efficacy LEDs, more efficient optics, and higher efficiency drivers. An improvement of 10% at the driver, 5% in the optics and 10% at the LED will produce the following results:

Total actual lumens per LED = 144.3 (@ 500mA)
Total luminaire lumens = 1010.1
Actual driver LED load = 12.6
Total driver efficiency at actual load = .93
Actual driver watts at 120VAC = 13.55
System lumens per watt = 74.55 lm/W

  1. Further improvements in thermal design may also produce additional gains in efficacy by increasing lumen output without adding any additional power.

This is a common issue with designing LED products. Data sheet values simply do not stack up as they might seem and represent values that are not representative of application conditions. This applies to LEDs and drivers alike and will vary by product lot as well.

Then what happens is…

So, you dig around and find even better LEDs and drivers, have a custom optic made that reduces power and produces the best total package. Perhaps not at the 100lm/W you wanted, but close. Customers love it and you can make a profit from it, so off to market you go!

About this time, you will receive a notification from the LED manufacturer that their new version of the LED you are using will be discontinued at the end of the year, to be replaced with a Gen MCMVLXX product that will produce higher lumens by 10%, and operate at 3.1 Vf, while operating at a higher Tj temperature with less lumen loss.  The driver manufacturer will also send notification that it is out of stock on the driver selected, with no firm date when their Chinese vendor will deliver new inventory. The optic manufacturer will then announce that the optic you chose is not compatible with the Gen MCMVLXX LED update, but are working on it. This all means re-testing and re-evaluating all of the decisions made before, and potentially necessitating revisions to UL listing and investigations that could lead to re-testing there.

Welcome to the world of LED product design and development! 

Seriously, while this exploration is fictitious, it does represent the variables that make designing around component manufacturer data unpredictable, if not completely unreliable. There are some take-away’s from this:

  • Never assume you will get the lumens out of an LED that are shown in data sheets. Read all of the data and make corrections that more closely resemble actual application conditions – then subtract another 15% to be safe.
  • Never assume that drivers will deliver exactly the name-plate current and Vf. When in doubt, test the selected product under the conditions it will be used under. Also note that efficiency numbers are generalizations that rarely match actual application conditions. The only way to know what the exact efficiency is, is to test load the driver in question with the intended LED / LED array.
  • Never assume that optical manufacturer efficiency data is correct, or even based on actual test data. The difference in realized optical efficiency and manufacturer data can be significant.
  • Thermal conditions, for the driver as well as LED have a large impact on lumen production and system efficiency. You cannot have a system operate at too low a temperature. Also, remember that data provided is rarely realistic to actual application conditions, so this alone will have a significant impact on system performance.
  • A last side note: Verify system performance under all line voltages anticipated. Just because a driver functions at 120VAC on a bench for 5 minutes, does not mean it will work at 277V after 12 hours continuous operation. Dimming issues are far more common at high voltage (277V) than they are at 120VAC, so test at both, through the entire dimming range.
  • Oh, yeah… dimming driver are notoriously bad at holding efficiency, even at full brightness – and fall off as the product is dimmed from there.

I propose that all pursuits of a color quality metric represented in any form of numeric value based on averages of performance over any number of color samples is wholy inadequate and a wast of time. We have been using such a system for far too long, with too many questions and related surrounding quality issues unanswered to continue with such a weak approach. I suggest that we pursue a Lighting Qualities Classification system that encompass eight (8) core variables that are critical to identification and selection of lighting products. This would be represented in a similar fashion as the successful Ingress Protection (IP) rating system already in use.

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Zero Flicker Task Light

Posted: January 21, 2016 in Light Meters, Tasca
Tags: ,
The Tasca task lighting head. My pet project for more than 6 years now.

The Tasca task lighting head. My pet project for over 6 years.

 

When I created Tasca, I had several goals in mind:

  • Strong light output  – Check – 800 lumens is top of its class
  • Smooth wide light pattern – Check – 78 degree beam pattern with no hot spots, no streaks, no rings, >200Fc at 18″
  • High color performance – Check >80CRIe standard @4000K, moving to >90CRIe @4000 or 5000K in latest models
  • No sparkly LED arrays – Check – single high quality COB array source
  • High efficiency – Check – >70lm/W total fixture efficacy
  • Tough and Ready – Check –  examples have been in operation 24/7/365 in shop environments with zero failures
  • ZERO FLICKER – Check – see below

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The original idea for the lighted magnifier was for inspection and reading small print on tools, which are generally done in a fixed location. The intended use was for continuous periods of work that made battery operation an issue. Mainly, the initial thinking was to turn it on and leave it on for the duration of a project. So, with it in hand and in use, I found in a short time it was being used for much more than its original intent. The magnifier lens in its unlit state is excellent in capturing ambient light, so I had it in mind that one lighted unit for the very tight and difficult work was great, with an unlit version for all other tasks. Problem is, the lighted unit provides over 1,780 FC on the target, transmitting over 700 FC to the eye at 4″. The unlit version produces no more than ambient levels, and if your head shades the ambient light, that is cut considerably. So, when comparing the two in actual use, the lighted version simply knocks the stuffing out of the unlit one. This meant I needed to cut the umbilical and create a battery powered version.

Adding a battery power pack to the Magnifier was found to be a desirable addition after finding the lighted unit so useful.

Adding a battery power pack to the Magnifier was found to be a desirable addition after finding the lighted unit so useful.

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A little industrial chique tribute to 2015 Year of Light.

A little industrial chique tribute to 2015 Year of Light.

Actually, this started as a rough lab test experiment applying thermal transfer pipes (copper pipes filled with water) to move heat from an LED platform to a simple back plane surface. The experiment included bending the pipes, soldering them using silver bearing solder, and operating the system at various angles to see the effect these had on performance. Somewhere along the line, an idea formed of making this into a wall piece, creating an industrial-chic, which led to adding a cut down reflector, and using the SLA printer to create an industrial tech representation of a flame rising from the reflector. The square cut in the diffuser aligns with the connected graphic on the back plane, and the stenciled number 15 simply represents the year.

The graphic alignment with the diffuser negative space connects the back-plane to the foremost diffuser component.

The graphic alignment with the diffuser negative space connects the back-plane to the foremost diffuser component.

The driver is housed in the FDM printed housing below the light source on the back plane, with a dimmer. Total power to the source is 19W, while the LED is 95CRI 3000K. Note that the overly red hue to the background, and slight magenta appearance of the white graphics are all issues with the camera dealing with the red-enhanced LED source, which creates high CRI, with a 90 R9 value, but in reality is a distortion of spectral power that the human eye does not readily see – but mid-range camera image sensor algorithms cannot accommodate.

The diffuser is intended to interpret a flame, or gas light sock.

The diffuser is intended to interpret a flame, or gas light sock.

 

The thermal pipes move 19W of energy from the LED platform to the back-plane - which is where the whole project started.

The thermal pipes move 19W of energy from the LED platform to the back-plane – which is where the whole project started. Cutting the back half of the reflector out provides light to the wall and plate surface.

The retro black egg - origins unknown.

The retro black egg

I found this little light on ebay at a lunch money price, so couldn’t resist. It started life as a Hamilton Industries (Chicago) lamp model 60, made in Japan in the early 1960’s.   It used a 12V magnetic transformer and a resister to provide a dual level light control of its 20W signal lamp. The amount of light it put out was barely visible in the presence of any ambient light. Meanwhile, I had a cute little key-chain wireless remote controller for less than $14 from LED Supply that delivers PWM dimming and on-off control of 12VDC LED loads. I stripped the guts out of their kit and put them inside the base of the fixture. The little lighting head was about the right size for a 12V MR16 lamp, so rather than re-invent that wheel, I just retrofitted the head to take a bi-pin socket and planned to use a retrofit MR16 lamp to deliver the light I wanted. That ended up more of an issue than I expected. First, after testing of all the LED MR’s I had around, only one brand would operate and dim effectively when run on DC power. The rest were poor dimming on AC power, but on DC they were miserable. On the LED Supply remote dimming module, they were useless. The lamp I ended up with was a Philips Enduraled product, and it will dim down to around 10%.

The remote control acts as a panel control when nested in the base, and as a remote control with cute antenna when separated.

The remote control acts as a panel control when nested in the base, and as a remote control with cute antenna when separated.

The remote control is a bit of fun, as it has an antenna that works well with the antenna arm on the fixture, so they seemed a great match. I printed a holder for the face of the power supply (now control) enclosure at the base of the fixture to hold the remote, which makes it a simple panel controller when the remote feature is not needed. When the light is used to wash a wall or light art or some other function besides a desk lamp, the remote can be removed and control the fixture from across the room. The power supply is a simple 12VDC wall wart, while the base houses only the remote control electronics now.

The base now incorporates the remote in a recessed compartment.

The base now incorporates the remote in a recessed compartment.

The base looked in need of a bit of dressing up, so I printed a retro-turbo trim ring to surround the remote control mount on the SLA printer and painted it with VHT fake chrome to give it a sand-cast aluminum look. I also printed the same part on the FDM printer for comparison. I’m throwing in two images of the raw prints to show the difference in surface quality one gets between these machines. Obviously, for parts that include details that will be hard to sand and fill, the SLA process is superior. For parts that need to be strong and can be easily finished, the FDM is the go-to tool.

The lighting head uses an LED MR16 lamp for its optic and driver components

The lighting head uses an LED MR16 lamp for its optic and driver components

So, this little weak black egg ebay find has been transformed from a barely functional desk lamp novelty, to a bright, useful, remote controllable, dimmable, black egg turbo trimmed LED light novelty. I’m a fan of the 50’s and 60’s design aesthetic, so this one felt right and was fun to put together.

The turbo fins look very rocket-man when the egg is closed up

The turbo fins look very rocket-man when the egg is closed up

 

 

 

 

 

 

 

The remote facilitates using the light as a wall accent, or ambient uplight, controlled from elsewhere in the room

The remote facilitates using the light as a wall accent, or ambient uplight, controlled from elsewhere in the room

With the remote out, the light can remain on, lighting the turbo louver as a night light

With the remote out, the light can remain on, lighting the turbo louver as a night light

The ebay purchase

The ebay purchase

The cord was ugly and the closed appearance rather out of alignment and boring

The cord was ugly and the closed appearance rather out of alignment and boring

While FDM 3D printed parts (top_ are strong and easily finished, in fineer detail work, they lack fidelity and smoothness. The SLA (bottom) part is much smoother, requiring less finish work, but are less durable. In this case, the FDM is printed at its finest setting, the SLA at its coursest, so the contrast here is greater when the SLA is pressed to maximize reolution. Both took 2.5 hours to print.

While FDM 3D printed parts (top_ are strong and easily finished, in fineer detail work, they lack fidelity and smoothness. The SLA (bottom) part is much smoother, requiring less finish work, but are less durable. In this case, the FDM is printed at its finest setting, the SLA at its coursest, so the contrast here is greater when the SLA is pressed to maximize reolution. Both took 2.5 hours to print.

 

The Purple Light ‘UV’ Cure Cube

The Cure Cube is used for curing SLA 3D Prints created on the Form Labs 1+ printer. Exposing SLA prints to 405nm "UV" light increases strength and creates a harder surface for final finishing.

The Cure Cube is used for curing SLA 3D Prints created on the Form Labs 1+ printer. Exposing SLA prints to 405nm “UV” light increases strength and creates a harder surface for final finishing.

While not particularly visible to everyone in the SSL universe, over the past few years one area of interest in LED product development for me has been in use of 405nm LED light sources to cure various plastics materials. The advantages are lower power requirements and reduced overall heat in the cure zone over conventional fluorescent or HID light sources. This has been of particular interest in curing fiberglass resins manufactured by Sunrez. The typical demand is for between 200 and 1,000 µW/CM² at 400-405nm wavelength. The use of LEDs allows us to generate exactly that without the waste of visible light, and longer wavelength power the resins are not reacting to. In one project, we were able to replace a 1,500W HID light source with a 120W LED light system that produced faster cure times with less than 10% of the total power, and virtually no heat added to the heat generated by the resin’s exothermic reaction to the curing initiator. Since then, we’ve built 405nm light cure fixtures ranging from 1,200W to 25W.

In this case, I needed to cure 3D prints we generate on a Form Labs 1+ 3D SLA printer, and do so in an office environment without exposing other materials and occupants to UVA light output. The material used in the print process is acrylic based, with chemistry that is photo-reactive to 405nm. The actual prints are made using a UV laser source. When the part is removed from the printer it is washed in alcohol (91% IPA), rested for a few hours to dry the alcohol off, then placed in this cure cube for an hour or more, depending on the thickness of the final component. The end result is a hard first surface for finish sanding or painting, if necessary, and a more rigid part as a whole (less flexible).

The cube is simple, with vent reliefs top and bottom to encourage ariflow. The flush switch on the top cover was created using 3D printing processes for the slider and body, as well as top and bottom cover.

The cube is simple, with vent reliefs top and bottom to encourage ariflow. The flush switch on the top cover was created using 3D printing processes for the slider and body, as well as top and bottom cover.

The cube utilizes a simple aluminum housing, with FDM 3D printed top and bottom covers. The top cover houses a single Recom 500mA driver, slide switch and wiring terminal block on a Tasca LED driver circuit board.

5mm 450nm LEDs with a FWHM distribution of 60º, 25 per side and top (125 total), operating at 20mA each, mounted to custom circuit boards sourced at Express PCB. Each board connects the LEDs in parallel, while the boards are connected in series, resulting in a 500mA, 15.4V circuit, totaling 7.7W. The boards and internal exposed surfaces inside the box were then covered with White Optics 98 matte material to increase total light energy and diffuse The light energy at 405nm is roughly 600 µW/CM².

The bottom surface includes a glass plate where the product sits in order to make any possible stickiness of a part from adhering to the White Optic material below.

The interior of the cube is covered with White Optics 98 material for optimizing light energy re-cycling.

The interior of the cube is covered with White Optics 98 material for optimizing light energy re-cycling.

The housing was powder coated matte black polyester to make clean up easy and the box look nice. The overall interior dimensions of the box are 1″ larger than the total build volume capacity of the printer itself (5 x 5 x 6.5), as any over-sizing is unnecessary. This produces an optimal match between the location of the LED sources and any part the printer can produce.

The Cube is powered by a remote plug mounted 24VDC power converter.

The operation of the box is simple enough. The box is lifted up, the part is set on the base, the box is set over the part, and the light is turned on by sliding the switch to the on position.

Simple and compact is the order of desktop manufacturing, and this fits that model perfectly.

A look into the box lighted up and ready to accept parts.

A look into the box lighted up and ready to accept parts.

Testing so far has shown the cube can cure raw resin from liquid to fully hardened in less than an hour, and strengthens prints in that time or less. The heat generated from this arrangement is so small, there is no chance of any part being warped or affected by the process, other than the desired results of becoming stronger.

For parts to be left unfinished, that are desired to be used over extended periods, we coat the finished parts in either acrylic or polyurethane UV inhibiting clear coat, gloss or matte. This stops ambient room light or daylight exposure from making the parts brittle over time. I am building a second copy of this cube for completing extended testing of samples of the materials we are using to verify clear coat effectiveness, behavior of the print material over long exposure periods, and the behavior of these low cost LEDs over time. A commercial version of this cube could be made using more robust LEDs, but the costs would be significantly higher as well. In the current configuration, the LEDs only cost $0.60 each, so should they last a couple of years in use, replacement of the populated boards is a simple task, while the cost of higher power LEDs would have increased the cost of the entire end-product by as much as three times.

There is also an additional version of this same approach in using Red/Blue light sources for use in plant seedling starts. We’ve found tests with common rye and barley grasses, the time from germination to hearty growth ready for planting is accelerated significantly. Using an enclosure like this allows the plants to be exposed to intense light for extended periods of time (18 hours or more) without polluting the surrounding environment with the ugly light, just as the enclosed cube protects room occupants from exposure the the UVA light. In either case, the cube can be used in any room environment comfortably and safely.

So this gets us off the ground and is D1 of 52 in the series. As I’ve noted at the start, this is an exercise in making progress, and putting SSL to work. This is not a particularly exciting product in and of itself, but it is one that will be used regularly, which more than makes up for its lack of marketing sizzle for the masses – at least in my book.