Rule of thumb in powering LEDs-prioritizing longevity over light output.  - Page 1
Forum section: electronics / projects

author: cdev
author_rank: Super Contributor
timestamp: October 27, 2018, 08:29:31 pm
content: I want to install some low voltage warm white LED spot lighting for safety and I want it to last a very long time so I don't ever have to repair it. It might be in inaccessible places, etc. Can I just derate it, if so by how much (a rule of thumb) Ive noticed that when I do that they last much longer and dont get dim, but my observation is not based on numbers, just my observation.In contrast it seems that LED light bulbs bought to replace conventional bulbs have a high attrition rate and so I have a bunch of them. I think I may just try to scavenge the remaining LEDs out of some of them to see how that works.I think their short life is probably because they are designed to run kind of hot.The LEDs themselves are probably fine and its the driver circuitry thats failing.Are there any papers that give an overview of the factors impacting LED longevity in a general way?

author: Buriedcode
author_rank: Super Contributor
timestamp: October 27, 2018, 11:21:32 pm
content: I don't have much experience with them but I assumed (perhaps wrongly) that its because often they are for hanging lights - with the (already running hot) driver sitting directly above a hot LED array with little or no ventilation. Both are running at their limits anyway, and their lifetimes are probably given for a more modest temperature range (= lies).Although it'll take a while I would be interested to see a comparison of lifetime for hanging vs "lamp" arrangement. Sorry, its not really what you asked for, I'll just watch the thread

author: cdev
author_rank: Super Contributor
timestamp: October 27, 2018, 11:29:52 pm
content: 'lamp' for me lasts longer than hanging or sideways.

author: SiliconWizard
author_rank: Super Contributor
timestamp: October 27, 2018, 11:54:23 pm
content: Quote from: cdev on October 27, 2018, 08:29:31 pmThat's what I have observed as well on a number of LED bulbs.Whether it's intentional, just bad design decisions or mainly cost reduction reasons, I don't know and it doesn't really matter. Most of the home LED bulbs are crap.Quote from: cdev on October 27, 2018, 08:29:31 pmYes, the drivers fail first. They are usually not properly heatsinked and the components are low-quality.The LEDs themselves will end up degrading as well when running too hot. We're just lucky enough that the drivers fail before they end up catching on fire.

author: texaspyro
author_rank: Super Contributor
timestamp: October 28, 2018, 04:45:04 am
content: My house has over 300 bulbs (in ceiling mounted cans)... all are now LED. I bought all my LED bulbs from am ebay seller that sold store returns (probably because they did not work with some dimmers). Most are Sylvania (made by Lighting Science Group). When I did the retrofit retail pricing for the LED bulbs would have been over $14,000 dollars. I got the "used" bulbs for less than what I was paying for hot-wire bulbs. Then LSG recalled a lot of their bulbs and they sent me brand new replacements... I'm fixed for life.I have had two LED bulbs fail in the last 5 years (before I was replacing at least one halogen bulb a week... and if the halogen was in the kitchen it usually took out a couple of other bulbs and the dimmer). Both failed bulbs were from the same socket.My LED bulbs are old-school designs with massive aluminum heat sinks (over a pound of aluminum in the PAR38's). Newer LED bulbs are way too aggressively cost reduced. Virtually no effective heat sinking.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: October 28, 2018, 06:02:35 am
content: While the following is specific to one group of LEDs it might give you some feel for the relationships. I would be very cautious in extrapolating these numbers to other LEDs, but the trends are probably not totally different.https://www.led-professional.com/lifetime-calculation-of-white-hp-leds-from-16-000-hours-aging-data

author: cdev
author_rank: Super Contributor
timestamp: October 28, 2018, 11:47:24 pm
content: Thank you, this info will be really helpful in deciding how to do my spot lighting.I have a dichroic filter, shaped like a quarter circle which I acquired decades ago- it was used in some kind of spectrometer made by OCLI in Northern California.It contains the entire rainbow and its very very useful in scoping out the color bands of any light source quickly, in a glance i can see how it diverges from a perfect spectrum. It may be useful in evaluating how much LEDs have aged.

author: David Hess
author_rank: Super Contributor
timestamp: October 31, 2018, 05:47:49 pm
content: It is the electronic ballasts which are unreliable. Maybe somebody makes a high reliability one but I do not know who.The obvious solution is to power the LEDs directly from DC since even DC ballast circuits could be unreliable.

author: Kjelt
author_rank: Super Contributor
timestamp: October 31, 2018, 06:34:39 pm
content: The ballasts have two weak points, one was already named:temperature.The second is on/off cycles. The led lamps from decent manufacturers mention the guaranteed or some max. amount of on/off cycles.

author: Synthtech
author_rank: Regular Contributor
timestamp: October 31, 2018, 07:03:19 pm
content: I used high quality name brand $34.00 LED lamps in my retail store that were very good but of course the dirty little secret of LED domestic and commercial lamps is that the longevity rating for them on the box is deceptive - their light output falls off quite rapidly, they may last so many thousand hours but after a year of 8 hour a day use they have lost 15-20 percent of their light output. I found myself changing them because they were dimming, not because they failed.

author: Ice-Tea
author_rank: Super Contributor
timestamp: October 31, 2018, 07:04:47 pm
content: If you keep the driver out of the equation: derating for the LEDs on its own means very little, its the temperature that's the killer. Derating it to 25% but having piss poor cooling will probably see it fade a few years anyway. Properly heatsinked LEDs can last a *very* long time, even when running them at full spec.

author: metrologist
author_rank: Super Contributor
timestamp: October 31, 2018, 07:11:33 pm
content: Quote from: Ice-Tea on October 31, 2018, 07:04:47 pmYeah, nobody want's that. No profit.

author: tpowell1830
author_rank: Frequent Contributor
timestamp: October 31, 2018, 07:45:57 pm
content: Big Clive reviews and tears down a lot of LED lights. If you don't watch Big Clive's videos, I have attached a link to his channel.https://www.youtube.com/user/bigclivedotcom/videosHope this helps...

author: texaspyro
author_rank: Super Contributor
timestamp: October 31, 2018, 07:58:45 pm
content: The standard for LED lamp longevity is a decrease to 70% of rated output. I have a few bulbs that have been on 24/7/365 for over 10 years with no discernible drop in light output. I did measure one PAR20 bulb in my integrating sphere after 5 years and it's output actually increased a few percent. I just tried to check it again last week, but the ink that I wrote the value on had evaporated...

author: Crazy_Pete
author_rank: Regular Contributor
timestamp: November 01, 2018, 06:01:07 am
content: Hahaha i came home to what fortunately had a glass table underneath it. A mentally disabled fellow (not being funny, his mother suffered a wartime injury as an innocent civilian victim while pregnant) who is associated with our co-op decided to be helpful and put 50W Halogen Lamps in a light circuit rated MAX 10 watts for LEDs. I came home to a terrible smell and various light parts, burnt melted plastic and other charred bits from the Ceiling all lying on the large Glass Dining Table. Had this stuff fallen on the hardwood floor it might have been a real problem. Point is always run cooler if you can and fer Pete's Sake (pun intended) SAFETY FIRST! :-)Thanks,Crazy Pete