Application Note: Easy Solution to LED Wall Washing Color Problem

Remember our color temperature drifting in our LED wall washing application note? No? Click here to read all about it Well, as you may recall we had 6 high power LEDs on a linear board to be installed either in a ceiling or in a floor along a wall. The LEDs were fitted with large 3/4-inch diameter can-type prismatic, directional diffusers. The problem was that the LED manufacturer’s binning for accounts buying less than a zillion LEDs leaves something to be desired. Add to that the fact that the contract manufacturer didn’t assemble these first using LEDs from one lot and then progressing to the next but rather a mix and match approach as they went along. We were expecting the LEDs to be warm white but what we got was anything from deep amber to pink with several shades of yellow, orange, and green in between.  There were hundreds of these boards made and even with the solution of pulling the surface mount LEDs off the board and binning them by color on our end, we were faced with the prospect of 30 – 40% board loss. Ouch!

Well, using all of my artistic color theory I learned in college another engineer and I came up with a novel solution that is not only simple enough to be manufactured in-house but dirt cheap as well! I am hugely familiar with optical filter design in addition to light, light properties, and light measurement and knew that the way to cancel out a particular color was to use it’s complementary color in a gel filter (optical filter made of plastic, glass, or even gelatin which is where the name comes from – think Kodak Wratten filters) of some transparency level other then totally opaque. The other engineer assigned to the project came to the same conclusion at the same time separately from me – clever guy!  Now we could have gone out and bought expensive, ready-made optical gels but during the testing stage we would need to go through multiple shades of a particular complementary color to find just the right shade of complementary color to correct an LED. Not to mention that we would need several different complementary gel colors to correct for the various shades of LED colors PLUS the fact that we would probably need several levels of opacity since we had several strengths of each color from the LEDs output (i.e. amber, dark amber, and really dark amber).All this trial and error testing would leave us needing a huge library of color gels which would be a gigantic expense.  We both knew that the best way to do this would be to manufacture the gels in-house. I had done something similiar on a different project where I needed colored lenses to cover LEDs on an in-house manufactured vinyl instrument panel label – I had used ink-jet transparency film to print the LED lenses. BINGO! We could print various shades of the complementary colors we needed at various opacity levels on transparency film in my desktop ink-jet printer! We could print strips of 1 or 2 inch squares with each succesive color a darker or lighter shade of the color we thought was complementary to the LED colro we needed to correct. We could print all of these at whatever opacity we needed. In this way, we could hold the strip over the LED and cycle it through the squares on a strip and see it’s effect on the LED light ouput color in realtime. Testing with a light meter revealed that the gels reduced the light output by well less than 10%, which in this case was not a problem since the LEDs were to be operated at a power rating slightly ABOVE the design spec. The other engineer and I were able to come up with the 6 or so colors we needed and at what opacity levels we would need all for the cost of one box of ink jet transparency film ($15.00) and our time. As it turned out, this was a HUGE time saver as well. Taking the SMT LEDs off to correct the problem the board would require about 1 hour per board plus the time of resoldering a new LED on to a new board (the metal-core board would be destroyed taking the LEDs off). Anyrate, we settled on 5%, 10%, 15%, 20, and 25% opacity so we had 6 colors at 5 opacity levels for a total of 30 different types of gels. Once the testing was done and we had our selections, we set about manufacturing the actual gels to fit the LEDs. Here I took each color/opacity level and printed it out on an entire sheet of ink-jet transparency film (along with some text indicating what color and opacity level it was so we wouldn’t have any binning mistakes later). Once all 30 combinations had been printed in this manner, our production department set about punching out 3/4-inch circles using a hollow punch and a hammer. We got over 150 circles per page. We used plastic cups labeled with the color and opacity level and these were filled as the puncher went along. The entire punching process took about 4 hours – less than the time it would take to yank the LEDs off of 5 boards! Once all the punching and binning was done, then we went about correcting each LED on a board. The 3/4-inch round gels were designed to fit right in to the recess at the top of the LED’s can diffuser/lens. The fit was perfect! We would still need to do a little trial and error testing by occasionally swapping circle gels onto and off of an LED until it was corrected to the best of our ability. Once a gel was found that worked well, it could be glued into place with a few dabs of quick drying optical epoxy on the edges. Once a few had been done, the process got really easy and quick. We did find a few oddball LEDs with weird in-between colors in their output that required either printing and punching a new gel set or in a few cases, stacking gels to achieve the best possible correction level. For example we had an LED with orangish output that when we applied the bluish-purple complementary gel, shifted to a slightly green output which required the application of another gel of purplish-red to correct. There were a few LEDs that had colors that kept shifting around no matter what we did – these were chocked up to loss.

It wasn’t elegant but it was cheap and effective and will ultimately reduce the board loss to the barest minimum -  our test batch sent to the customer had LED with output colors well within their design specs so we are confident the solution will pass muster. I’ll let you know as soon as I hear back.

Technorati Tags: Innovative Lighting Design, Tools of the Trade. Tags: architectural lighting, architectural lighting design, architectural lighting design tools, color filters, colored filters, correcting led binning, correcting led color, designing with light, gelatin filter, gels, home made filters, homemade filters, homemade gels, led architectural lighting, led binning, led color, led color temp, led color temperature, led filters, led gels, led lighting, led wall washer, led wall washing, lighting design, lighting design tools, lighting designers

New Architectural Lighting Blog Image Gallery!

Just a quick note to let you know that I have posted a gallery page (click the “gallery” tab at the top of the blog just under the header or click here) . Currently it contains a small collection of some of my 3D renders and sketches of concept LED-based architectural lighting fixtures.  I will add to it as I can. Let me know what you think!

Application note: LED Use in Wall Washing Applications

Introduction

LEDs are quickly expanding into the world of architectural lighting into many specific applications once occupied by metal halide or tungsten halogen lamps (think MR16 sized) such as spot lighting, marker lighting (stairs, railings, doorways etc..), and wall washing. Its this last one that I want to talk about here – particularly the pitfall of color temperature as it applies to white LEDs.

Wall Washing? I don’t even clean my windows!

Multi-colored exterior wall washer lights. Courtesy led24.de

Wall washing is when a light or series of lights, usually but not always colored, are positioned and often aimed (physically or through the use of lenses) to spread a wide swath of light onto a wall. Colors can be used for moody effects and colors can be blended from lamp to lamp even within a single fixture. You’ve seen this a lot on the exteriors of large buildings – particularly modern designs or highly stylized buildings such as theaters, casinos, hotels, arenas, etc… Sometimes wall washing – really a sub- type of effects lighting – is used to great effect indoors as well – not only on larger expanses of vertical walls (you typically see larger metal halide or halogen lamps used for very large walls) but equally well on smaller walls, particularly when using LED fixtures.

Why use LEDs for wall washing?

Well for several reasons really. Generally the same reasons for using LEDs in most any application they can fit into – cost savings on both maintenance and energy use, heat reduction, ease of dimming/cycling, and size reduction. I’m not going to go into a full-on discussion of LEDs versus lamps (I’ve already done that) here but I will talk briefly about their advantages in wall washing applications. Thanks to the LED manufacturers (particularly Cree and Osram) and their latest generation of high powered LEDs with their much increased power output – LEDs can be put to the task of replacing the typically hot, energy hogging, high maintenance metal halide and halogen spot lamps. Here are some comparisons in no particular order:

• LEDs are much more efficient in their energy use than halogen or metal halide lamps leading to a cost savings in energy over time.
• They are much smaller even when considering the use of additional focusing lenses for wall washing/spot applications, they do produce heat but far less heat and what is produced is thrown out the back and can be easily directed away from the fixture (the fixtures themselves – often extruded aluminum can be heatsinks in their own right) – so the light itself is not hot whereas a metal halide spot light tightly focused on a wall could melt the paint right off if care isn’t taken. This also means they can easily get wet outdoors since an LED wall washer throws no heat in the light, the lens or window sealling off the LEDs won’t heat up and crack when hit with cool water like it can with lamps throwing lots of heat.
• Due to the really small size of LEDs (even high powered ones), one can create substantially smaller fixtures – even when considering the relatively small MR16 type halogen lamps the LED fixture is generally smaller.
• LEDs last, on the whole, waaaaaayyyy longer than lamps. Halogens typically last under 2,000 hours of continuous use and metal halides typically under 10,000 hours but almost all LEDs have lifetimes of 100,o00 hours of continuous use. While I’m on that subject – the lifetime of a halogen or metal halide lamp is defined as “when it’s dead and won’t turn on anymore” where as lifetime for an LED is defined as 70% or less of it’s initial output” meaning LEDs won’t typically just blink out but will dim and/or color shift when they are considered at the end of their life. So, due to the extreme lifespan of LEDs – you get a huge boost in the maintenance savings since your not out replacing bulbs all the time. Kewl
• Since LEDs are solid-state devices, they can be turned on and off at will with no ill effects whereas turning lamps off and on can over and over again shotens their lifespan. They can also easilly be dimmed but so can lamps – in fact lamps typically only need a small rheostat to dim whereas LEDs need a more complicated pulse width modulation module (PLM module) for dimming. Since the power supplies (called drivers) are solid-state themselves, they are typically small and can allow for all sorts of new, innovative features such as computer control and real-time feedback on LED parameters plus LEDs are all low voltage DC where as lamps, especially high-powered wall washers, tend to be AC although a lot of low-voltage halogen lamps are used but their output is not particularly ideal for large wall washing applications.

What are some of the pitfalls of using LEDs in wall washing applications?

Well, the initial cost of LEDs is generally much higher than traditional halogen or even metal halide fixtures and due to that initial cost, it can take a long time in cost savings from efficiency to pay for the expense. Power output – lets face it, it takes way more LEDs together in an array (at much greater cost) to make the same power output of a modest halogen spot lamp which costs like a tenth of what the LED array would. The more LEDs you use, the more drivers you will need and if your utilizing dimmers or computer control, more LEDs increases the complexity of the wiring. Lastly, color temperature – which isn’t really a problem with lamps, can be a BIG problem with LEDs. Colored LEDs aren’t as much of a problem but color temperature variation really comes into play with white LEDs. Non-colored lamps tend to be very consistent in color temperature between lamps but due to the complexity of manufacturing and how white LEDs are made, you can get considerable variance which must be delt with as I recently learned.

Color Temperature Variations

Well, this is the crux of this application note and the reason I am writing today. Color temperature. Color temperature (given in degrees Kelvin) refers specifically to the visual rendering of a white light as compared to that of an ideal black-body source where the temperature of the black body source causes it’s light output to match that of the compartive light source. The “warmer” the color temperature, the more yellow it appears (but the lower the actual color temperature 2700 – 3300 K – kind of weird huh?) and the “colder” the temperature, the more bluish it looks but the higher the color temperature is (+5000 K). What may look white to you at first glance may not be – it could be bluish, yellowish, or variations in between. Halogen lamps are black body sources and tend to be yellowish and metal halide lamps tend to be quite bluish but they tend to be quite consistent from lamp to lamp due to the physical properties of how they generate light (really, REALLY, hot elements and gasses) . LEDs being solid-state devices and there can be considerable variation in the manufacturing process. “White” LEDs are typically made by taking a blue LED chip and coating it with a yellow phosphor that glows or phosphoresces when hit by the blue light but phosphors of various colors (green, red, blue etc…) can be stacked in various thicknesses on top of various base LED chips (sometimes near UV chips are used) to create “white” LEDs. It’s precisely this amount of variability that can lead to color temperature problems in white LED applications. Generally, you would want to stick to one LED type from one LED manufacturer to eliminate possibly using different types of phosphor coated LEDs but even then the LED manufacturing process can produce considerable variability even among one LED type from the same manufacturer. Generally, LEDs are produced in large batches of 10’s of thousands of LEDs and all the LEDs from a single batch tend to but not always have similar color characteristics. Through the use of automated spectrophotometric equipment, LED manufactures can futher sort or bin their LEDs by their specific color temperatures – putting the more white LEDs together, the yellowish LEDs together, and the bluish LEDs together in smaller batches or bins. Depending on the manufacture and how sophisticated their equipment is and how demanding their customers tend to be – even amongst individual color bins you may still find some variation. The quality of binning tends to vary from manufacturer to manufacturer and it is often directly proportional to how many LEDs you order.

Prominence of color temp variation in LED color rendering varies with distance between fixtures & between LEDs themselves

Generally, you can get more picky about color binning when ordering huge numbers of LEDs and you have no say at all really when order less than a 1,000 pieces – something to consider. Generally, however, the variability from LED to LED within the same lot or reel tends to be ok with a few deviants. Its when you start mixing and matching from various reels/lots that you can really run into problems. In practical use, you may not ever notice that a

“white” LED isn’t quite white depending on it’s use – with spot illumination applications like down lighting and task lighting you may not notice particurlarly where you tend to have one LED or a very tight cluster of LEDS all emitting a narrow cone of light or the spot fixtures themselves aren’t that close to each other but the color shift is particularly pronounced in wall washing applications

where the light fixtures are very linear and you may have several inches between LEDs (preventing their output mixture until several inches to feet up the wall) and the fixtures tend to be put one after another in long strings. Walls tend to be like a blank canvas and where the light tends to be right up against that canvas, you really start to notice the color.

Practical Lesson

I know all of this since I recently worked on an LED wall washing application where the color of binned LEDs shifted all around even though the LEDs all came out of the same bin. The binning wasn’t terrible (it could have been better) but our contract manufacturer didn’t consitently use all of the LEDs from a reel before moving on to the next when populating the module boards. We had hundreds of linear LED modules with 6 high power LEDs on each and each with a prismatic, directional lens on them. Each was supposed to be a nice warm color around 3000 K. However, what we got were many, many LEDs that produced amber even dark amber LEDs that when placed up against a white wall, looked yellow – I mean you’d call these “yellow” LEDs

The effects of color temperature variation of white LEDs in wall washing applications

.

Plus we got some that were pinkish in color, greenish, and even orangish in color yet they all came from the same bin. These colors, even many inches above the actual LEDs would mix and create unattractive hues on the wall but were particularly noticable right above the LED. See my ugly illustration to the upper right to get an idea of what happens. Anyway, since the boards were all made up with the LEDs on them through no fault of our own, we quickly had to use our expertise and start pulling these surface mount LEDs off them and doing our own “binning” to get boards with uniform color outputs from each of the six LEDs. Was this a nightmare? Yes, but a lesson learned – check LED color temperatures wherever possible even if the LEDs all come from the same bin when the application demands it, like color sensitive wall washing applications. Make sure that lot/bin numbers are carefully checked when assembling devices from LEDs and stick to one lot or bin when placement of LEDs will allow for color mixing such as a linear array.

Conclusion

Well I hope my thoughts or rants made some sort of sense to someone. Let me know what you think. Have you had your own experiences with lousy color temperature variation in white LEDs – let me know?

P.S. The solution to this is…..

If you want to know what the quick, easy, and dirt cheap solution we came up with for this problem is – click here to find out

Technorati Tags: Innovative Lighting Design, Tools of the Trade. Tags: architectural lighting, architectural lighting design, architectural lighting design tools, color filters, colored filters, correcting led binning, correcting led color, designing with light, gelatin filter, gels, home made filters, homemade filters, homemade gels, led architectural lighting, led binning, led color, led color temp, led color temperature, led filters, led gels, led lighting, led wall washer, led wall washing, lighting design, lighting design tools, lighting designers

Clearing the attic

Well, it’s been a looooonnnnnnggggg while since I posted anything. It’s been soooo hard with other commitments within the company and outside the company but I am still pushing forward – albeit a bit slow. Thank you for all of the comments lately, it’s really nice to see that many of my readers are participating.  I have been invited by a couple of blogs for link exchanging which is really cool and that is something I am always open too. If your blog relates to architectural lighting in a meaningful way, then I am totally open to that. One thing that I am not really open to which has come up is that I link exchange WITHIN a post. Let me say that I am not offended by anyone asking so don’t worry about that but I am not going to place links/ads within the blog outside of the blogroll but thats not to say I wouldn’t consider it if there was some really deep connection on a technical level that would really enhance the post.

Well that’s it for now. I’ll be posting a small lighting application note soon.

Sticky: Second Phase of HYVE/Osram “LED-Emotionalize your light” Design Contest Starts

I just received a follow up email from HYVE regarding the “LED-Emotionalize your light” design contest. Here it is for any of my readers that have participated:

The second phase of the LED-Emotionalize your light! Idea Contest has started!

At this very moment the jury is selecting the 3 best ideas and designs out
of more than 500 contributions and the winners will then be announced on
Wednesday. The first phase has been a huge success with 505 ideas, 764
members, 6599 community evaluations and 2897 comments within 7 weeks and
still new ideas are submitted. While the winning ideas are waiting for
their announcement the three most active community members have already
been chosen: Congratulations to howman, LED Head and Classic!

Contest Phase 2
The focus of the second contest phase will be on refinements and further
developments. The 10 most interesting ideas are selected by the jury and
the community is forced to advance these contributions by further designs,
applications or technical solutions. Phase 2 will be closed on July 20th,
2009 and two weeks later on August 4th, 2009 the 3 contributors of the
best improvements will be awarded. The best submission will receive
1.000€. The second prize will be 600€ and the third prize will be
400€. But keep in mind, the three most active community members will be
rewarded as well. You have the possibility to comment on ideas or
improvements, to evaluate them or to leave messages on
www.led-emotionalize.com.

Social Networks
Beside the contest platform all participants and everyone who is
interested can join the LED-Emotionalize your light – Design Contest
group or the contest community on facebook. You have the chance to receive
the latest contest news on twitter and in case of questions contact the
contest team by sending an email to info@led-emotionalize.com.

We really appreciate your participation in Phase II of the contest. Become
a part of continuous success of creativity and open innovation by
reporting on the contest or forwarding this information to your creative
network!

Thank you for your support

Technorati Tags: lighting design , lighting designers , lighting design software , lighting engineering , Office Lighting , office lighting design , designing with light , lighting contest , lighting design contest , osram , hyve , lighting innovations , led emotion , led emotionalize , competition , led competition , lighting design competition

Dialux Videos

Using the website Truveo, I have found several Dialux-related videos from across the web.  I cannot watch many types of online videos from work so I cant tell you what they entail or what their quality is but it’s worth a look. Maybe one of my readers could comment back and let me know whats up with these? They didn’t look like tutorial videos (growns from the readers) but rather showcases of specific projects but I didn’t look at them all and again, I can’t view the videos themselves. Even if they are just showcase videos, it’s still cool to see Dialux in action!

Click here to checkout Dialux videos via Truveo

Sticky: HYVE Innovation Community in collaboration with OSRAM, are hosting an online idea and design competition

First off, let me say that I am NOT posting this late. I did not get this until 25MAY09 but the contest runs until the end of July so you still have time. I am posting the email sent to me by HYVE regarding this really cool contest. I am considering entering and I hope all of you lighting designers out there do too. Come on! Strut your stuff – you might win something. If any of you do, please post back here or send me an email with images and an explanation (short) of your design – I would LOVE to post them here! Here is the email explaining the contest:

We, the HYVE Innovation Community in collaboration with OSRAM, are going
to host an online idea and design competition in the beginning of May
until the end of July. The contest “LED – Emotionalize your light”
(www.LED-emotionalize.com) asks international light and design lovers to
share their ideas in the field of light designs using LED technology and
to create innovative and emotional mood light concepts. Moreover the
contest aims to generate feasible ideas for light solutions, which are on
the one hand easy to use and implement and on the other hand affordable
for everyone.

With the help of an easy to use submission procedure ideas can be
contributed, described with simple application scenarios and extended by
designs or technical solutions. Participants will not only have the
possibility to create their own Light design, but also to have it
discussed within the community. The community members can comment the
ideas of other participants as well as to evaluate or refine them.

The competition has already started and will run until the end of July
2009. Within the first phase new ideas and designs are collected and
discussed by the community. In the following second phase the best designs
and ideas are presented and jointly advanced by the community.

All participants of the competition have the chance to win valuable prizes
amounting to 7000€. The designs will be judged by a professional jury,
consisting of senior staff of OSRAM and selected professional
representatives. The selection considers community and expert evaluations
and will be based on creativity, innovation and emotionality of the
submitted ideas. Furthermore the most active community members in each
phase can receive valuable non-cash prizes.

The “LED – Emotionalize your light” Idea contest is supported by the
light producer OSRAM and the Siemens AG

The following link will guide you directly to the competition:
www.LED-emotionalize.com

Really cool designs have been submitted up to now. For example Luminous
speaker, which can change their colour according to the music or luminous
chairs which might change their colour if it’s happy hour.

So check out the competition and if you find this competition exciting and
interesting, we would appreciate it if you could report on our contest in
your blog.

Thank you for your support.
So there you have it – get going already – I want to see what you guys and gals come up with. I’ll try to enter and post what I come up with too. 

Technorati Tags: lighting design , lighting designers , lighting design software , lighting engineering , Office Lighting , office lighting design , designing with light , lighting contest , lighting design contest , osram , hyve , lighting innovations , led emotion , led emotionalize , competition , led competition , lighting design competition

Smart LED Parking Lot Lights

UC Davis parking garage. Photo courtesy of Cree.

Ruud Lighting/BetaLED along with the University of California at Davis have developed “smart” LED parking lot lights that reduce the energy consumption by 80% over the more traditional metal-halide lamps they replaced. The 50 LED light fixtures implement a two-level activity sensing system that dims the lights to half power when no motion is detected and then bring them back up to full power when motion is sensed. Along with conserving energy, drivers, pedestrians, lot attendents, and security personnel will now have visual ques to the presence of other drivers/pedestrians in the area. After two years of development and testing, the fixtures were installed in the UC Davis South Entry Parking Structure. The smart lighting system technology is being destributed via Cree’s LED University program. Very cool indeed!

Click here to read the full article from LED News

Technorati Tags: architectural lighting, parking lot lighting, parking lights, led parking lot lights, UC Davis, University of California, California Lighting Technology Center, Smart LED lighting, Smart lights

Submit your craziest, goofiest, or kookiest light fixture design pics

Here’s an idea. I am really interested to see what any of the light fixture designers of the world have come up with for really far out light fixtures, maybe while they were in design school or something. Don’t worry, I’m not going to swipe the designs or anything – indeed the weirder the better so these aren’t likely to be active designs with patents or anything. I’m sure you have come up with some kooky designs so lets see them! Please comment with links to pictures you have up on the web already or email them to me by clicking here (gif, png, jpg) Don’t be shy!

Maybe once we have a bunch, I’ll host a poll to get your opinion on which is the kookiest or most likely to make a real product (maybe with a prize or something…shhh).

Technorati Tags: light fixture, lighting design, lighting design contest, light fixture picture, crazy light design, kooky light design, goofy light design, creative light design

Announcing the Sketchup Graphics Blog!

I would like to inform all my readers that I have a new blog, the Sketchup Graphics Blog, that is about all things Sketchup. I have taken the Sketchup related posts from here and copied them over to the new blog. Sketchupgraphics.com will feature the latest news about Google Skethcup, Sketchup plugins, Sketchup tutorials, and more. Please check it out and let me know what you think!