Uh oh: "Detroit’s LED streetlights going dark after a few years" - Page 1
Forum section: electronics / general

author: IDEngineer
author_rank: Super Contributor
timestamp: May 08, 2019, 01:13:09 am
content: From our "Even LED lights need proper heat dissipation" department:QuoteReminds me of, but not nearly as bad as, the recall a few years ago of many millions of fire sprinkler fixtures. I don't know how that one worked out, but just imagine being on the hook for swapping out every sprinkler installed in buildings across the USA over a span of many years. Bet their insurance company was scrambling to find some fine print escape clause!https://www.detroitnews.com/story/news/local/detroit-city/2019/05/07/detroits-led-streetlights-going-dark-after-few-years/3650465002/EDIT: Here's just the first hit on fire sprinkler recalls. 35 MILLION UNITS are involved in the recall. Woof.https://www.cpsc.gov/Recalls/2001/cpsc-central-sprinkler-company-announce-voluntary-recall-to-replace-o-ring-fire

author: Psi
author_rank: Super Contributor
timestamp: May 08, 2019, 01:22:40 am
content: Sounds like someone has been buying in bulk those reject 100W leds from aliexpress.

author: floobydust
author_rank: Super Contributor
timestamp: May 08, 2019, 04:44:15 am
content: It's weird the lenses are meltingunderthe LED? More heat please.Detroit filed a $9M lawsuit, up to 20,000E-cobraLED streetlights. 10 year warranty "... Leotek ceased all communications" they've surely left the country. Berkley California also purchased 7,000 of them.

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2019, 05:33:43 am
content: Just the other day a friend of mine who is in the streetlight business was showing me some pictures he took of those lights. They get dirt into the optics which absorbs heat and then the lens darkens which makes it get hotter until it melts. Leotek is one of his competitors.There are some quite good LED streetlights but a lot of them are crap. The earlier generations were fairly pathetic, with efficiency no better than the old mercury lamps that got changed out decades ago for more efficient but hideously ugly orange HPS lights. Those old mercury lights weren't the most efficient things but they sure did last, I have lamps that were in dusk till dawn service for ~30 years that still work and still put out plenty of light.

author: floobydust
author_rank: Super Contributor
timestamp: May 08, 2019, 06:20:56 am
content: It has nothing for a decent heatsink, just flat aluminium plate with a zillion screws and a smooth top side.Whatever happened to fins?

author: AndyC_772
author_rank: Super Contributor
timestamp: May 08, 2019, 06:48:57 am
content: Failures like that do make me nervous, because clearly something has happened over a timescale that's too long to ever replicate in the lab prior to putting a product on sale.It doesn't take all that long for something that size to reach its steady state temperature. I wonder what it was?Did this "excessive heat" always exist, and it's only now been noticed because they've been looking for it?Or did the lamp work perfectly well for a period of weeks or months, but something *very* gradually degraded during that time leading to a thermal runaway effect, which meant a failure mechanism suddenly accelerated?Hindsight is a wonderful thing, but I wonder what (if any) evidence existed that more cooling was needed *before* putting a large number of units into service for an extended time?

author: Psi
author_rank: Super Contributor
timestamp: May 08, 2019, 08:15:51 am
content: Lack of engineering oversight on project.Streetlamps should have temp sensors and regulated their brightness to keep the LED/heatsink under 50deg C.(yes i know LEDs can run ok up to 80deg C but these are streetlights and longevity is a critical factor)

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2019, 02:33:50 pm
content: Quote from: Psi on May 08, 2019, 08:15:51 amThat may not help in this case, it's optical heating of the plastic lens, not the temperature of the LEDs and driver.

author: floobydust
author_rank: Super Contributor
timestamp: May 08, 2019, 05:50:55 pm
content: The lens melting might be a result of something else. The article said the streetlights blink, and burn up. It must be a potted blob for waterproofing, the enclosure has many seams.Usually I see electrolytic capacitors fail and then the power supply goes unstable, which might over-current the LEDs and cook everything.Optical heating? If you pass sunlight through those lenses, I would not expect them to heat up. Even a laser beam. Unless this is a new issue.Good engineering will consider and test results of a cap getting old or -50% in value. I have to do that because winter (industrial) designs are spec'd to -40C/-40F.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: May 08, 2019, 06:17:53 pm
content: Quote from: floobydust on May 08, 2019, 05:50:55 pmThe problem is not the light passing through the lens. It's the light not passing through the dirt on it.Light is absorbed on a small speck of dirt, which causes localized heating.

author: Synthtech
author_rank: Regular Contributor
timestamp: May 08, 2019, 06:49:24 pm
content: Not to mention that LED lamps simply fade over time. I had dozens of LED down lights in my retail store and they were well ventilated and I usually used the Phillips lamps designed for heavy use in places such as hotel foyers and even with 8 hours a day usage they lost around 20 percent of their brightness after 12-18 months and a lot of them started blinking within 24 months.Fading light output is the dirty little secret that manufacturers try and hide, when you buy an LED lamp you need to find the specification for how long the lamp is rated before it falls to 70% output and factor that into your cost analysis.

author: floobydust
author_rank: Super Contributor
timestamp: May 08, 2019, 07:59:58 pm
content: Leotek's E-Cobra datasheet:"Hi-flux/Hi-power white LEDs produce a minimum of 90% of initial intensity at 100,000 hours of life based on IES TM-21."I wonder how they faked that (projected) spec, maybe running at 1mA lol.

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2019, 10:28:21 pm
content: Quote from: Domagoj T on May 08, 2019, 06:17:53 pmWhich then causes the plastic to start turning yellow then brown, absorbing more and more of the light energy until a hole is melted right through it.

author: james_s
author_rank: Super Contributor
timestamp: May 08, 2019, 10:31:56 pm
content: Quote from: Synthtech on May 08, 2019, 06:49:24 pmThat's surprising that you had that issue with Philips bulbs. I have some of the old remote phosphor Philips bulbs in my front porch lights, I installed them in 2011 and they have been running dusk till dawn every night since then. About a year ago I took one out and put it side by side with a new one I never used and it looked identical. Good quality LEDs in a properly designed luminaire can last a very long time. Those old Philips bulbs are rated 50,000 hours to L70, ie 70% of initial output and so far I'm thinking mine might do it.

author: thm_w
author_rank: Super Contributor
timestamp: May 08, 2019, 10:57:38 pm
content: QuoteWas thinking they should be using glass lenses, but when you spend $154 per light, I'm not sure if thats realistic.At least they were smart to get a 10 year warranty.

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2019, 03:58:28 am
content: Everyone is using plastic lenses, every streetlight will have an issue with dust, dirt, bugs.Perhaps they used cheap low melting temp plastic. Polycarbonate seems to be good to 90°C/195°F, and 110°C gave a 1 year life.http://www.hubbell.ca/030~Lighting_Products/030~Resources/whitepaper-polycarbonate-and-acrylic-lenses.html

author: benbradley
author_rank: Contributor
timestamp: May 09, 2019, 04:20:19 am
content: Quote from: floobydust on May 08, 2019, 07:59:58 pmI've heard of some paper by Hewlett-Packard from early on in the original red indicator LEDs (1960s), that the light output dropped substantially over operating time. I would guess this became less as purer silicon was made for the semiconductor industry over the decades, but I wouldn't know, as I don't know the mechanism that would cause this. I've looked for that paper or something that mentions it, and I can't find it. Does anyone know what I'm talking about?

author: Cyberdragon
author_rank: Super Contributor
timestamp: May 09, 2019, 04:30:48 am
content: Quote from: floobydust on May 08, 2019, 05:50:55 pmLenses are not a critical part of the light producing system of a lamp anyway. If just the lenses failed, it would simply get weaker. Something else is going on making them burn out entirely.

author: Domagoj T
author_rank: Frequent Contributor
timestamp: May 09, 2019, 06:26:39 am
content: Quote from: Cyberdragon on May 09, 2019, 04:30:48 amThe failure comes from overheating, which is the result of a failed lens that traps the heat inside the enclosure.

author: james_s
author_rank: Super Contributor
timestamp: May 09, 2019, 04:49:22 pm
content: They're just cheap poorly designed luminaires all around. I've been involved in a side project relating to street lighting and we have quite a pile of different LED streetlight luminaires to test with. I've opened most of them up and had a close look and some are far better made than others. Some are far more expensive too though, so one has to make choices.

author: floobydust
author_rank: Super Contributor
timestamp: May 09, 2019, 09:03:41 pm
content: I think you can't make a decent LED streetlight and there is no need to. A sea of patents and most of us would get fired because we couldn't achieve the cost target designing for a (real) 10-year service life.There's also the "race to the bottom". Here's what you get forunder $1(4.5¥) in china. Yes it burned my fingers (50W version) andBigClivemeasured 126°C temperature on his "100W" version.I got one just to hang on the wall and remind me that engineering quality products means absolutely nothing now.The vendor admitted they hate selling them, they are cheap even by chinese standards. But a certain third-world country loves buying them, so they make them. I could never get the aluminium reflector or IC alone for $1, let alone the MCORE pcb or LEDs, bubble packaging, silicone gel, instruction sheet, or assembly. The low cost is stunning.If you're looking at streetlight bids and tenders, a low price is going to be very attractive and a 10-year warranty... of course the company will shut down in a few years to absolve any liability.Just like the crappy condo developers and builders. Make a junky building, shutdown the company afterwards and there is nobody to go after when structural/water issues arise years later.Meanwhile, it all paid for a Lamborgini or two and exec's are enjoying a ride in the sun.

author: amyk
author_rank: Super Contributor
timestamp: May 11, 2019, 12:15:18 am
content: Burnt lenses is something I'd expect to happen with projector lamps and such, not LED streetlights... I think the LEDs may have failed half-shorted and heated the plastic to the point of failure, and it's not the light itself that did it.

author: james_s
author_rank: Super Contributor
timestamp: May 11, 2019, 03:51:39 am
content: It's the light itself, and probably some radiated heat, some failed units have been examined up close. Crud gets inside and deposits on the lens. This causes it to heat up and darken which causes it to heat up more. Eventually some of them melt holes all the way through under the LEDs and then the light gets brighter. Others fail before this happens. The whole fixtures are poorly designed.

author: soldar
author_rank: Super Contributor
timestamp: May 19, 2019, 07:16:02 pm
content: I think every new technology and application goes through a phase of failures and correcting weak points. This is why aerospace, medical and other safety-critical applications prefer to stick with more proven technologies. I remember the bad caps epidemic some years ago. Now it is easy to see they should have seen it coming. The same with LED lighting. Some will fail and the industry will learn how to do it better.

author: floobydust
author_rank: Super Contributor
timestamp: May 19, 2019, 08:08:25 pm
content: Quote from: soldar on May 19, 2019, 07:16:02 pmNo - it's the sea of patents on the LED, lens, reflector, heatsink, housing etc.Everybody wants an edge, something to make their streetlight better than the rest, and the big dog companies have patented every little bit of IP. So you have to avoid patent infringement and compromise the design, and be cheap too. This has made home LED bulbs crap as well.example:"streetlight lens"patents 12,528 hitsIt's a myth LED lighting lasts 50,000 or 100,000 hours. If they haven't faded into almost nothing, the support electronics is dead. Or the housing corroded, paint flaked off, water gets inside.

author: james_s
author_rank: Super Contributor
timestamp: May 19, 2019, 08:20:12 pm
content: It's not a myth, there are good ones that do last as specified, but there is a lot of junk too. Making something that lasts like that costs money, too many people shop by price.

author: floobydust
author_rank: Super Contributor
timestamp: May 19, 2019, 08:57:03 pm
content: How much more is the cost of "really good" LED streetlights?Take two streetlight fixtures - (8hrs/day average on time):lasts 10,000hrs or 3.4 yearslasts 30,000hrs or 10.3 yearsSo union labour has to drive out there, bucket loader truck and replace the cheap lamp fixture three times, compared to once for the expensive fixture. Guys get to keep a job changing streetlights. I'd guess several $100 taxpayer's cost to do this, plus disposal/warranty hassles.The "really good" expensive LED streetlights may or may not be worth it?

author: james_s
author_rank: Super Contributor
timestamp: May 19, 2019, 10:30:34 pm
content: You're expecting logic and long term thinking, which is rare in bureaucratic projects like city streetlighting. When two contractors bid on a project, the one with the lowest bid is likely to win, two lights may have the same claims of lifespan and look similar on paper but one is half the cost. If it ends up failing years earlier the money has already been spent, the company that made it might be gone.

author: floobydust
author_rank: Super Contributor
timestamp: May 19, 2019, 11:31:28 pm
content: Yes it's a terrible analysis. It was a $185-million project.Most of the numbers are about using fewer (65,000 vs 88,000) streetlights due to LED's luminance.Preliminary quotes per cobrahead were $185 ea.Savings almost $3M/yr in electricity. No figures for any maintenance costs"Maintenance savings are more difficult to quantify than energy savings given the extraordinarycircumstances surrounding the failed condition of the previous system. Certainly the conventional need for relamping fixtures every 4-5 years will be eliminated following the substitution of LED luminaires, although they eventually need replacement as well(perhaps on a 15-20 year cycle)."Restoring Detroit’s Street Lighting System pdf

author: IDEngineer
author_rank: Super Contributor
timestamp: May 20, 2019, 12:03:43 am
content: Quote from: james_s on May 19, 2019, 10:30:34 pmThe best public contracts I've seen include a bond that the contractor must post against future claims. If the company goes out of business, the bond helps pay for it rather than the entire burden falling on the taxpayers. This protects the public from the standard dodge of "Do the job, then close that company and open a different one to leave the liability behind". I've most often seen this done for road construction where the new surface is supposed to be "guaranteed" for 10-20 years of useful life. The bond allows another company to come in and repair/resurface if necessary within the guarantee period.The cynic in me says that politicians don't always do this because they are in cahoots with the bidders.