LED light bulbs - temperature sensivity

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scribbled this interesting note:

Or a kerosene lamp???
-- John Willis snipped-for-privacy@airmail.net (Remove the Primes before e-mailing me)
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I have a camping 2-tube fluorescent lamp that runs on 4 D cells,runs 20 hrs on both tubes,40 hrs on one tube.Has a nice folding lamp housing so you can position it,and it's very compact. It cost only $12,made by Eveready,IIRC.
It came in handy last year for Hurricane Charlie.
Then I have one longer portable battery-powered single-tube fluorescent,designed to be installed in closets with no outlets,uses 8 AA cells,and has an external 2.5mm power jack that I made one long cable for that alligator-clips onto my car battery for a worklight,and another cable that goes to a 12V gel cell for inside use. That lamp cost around $9 IIRC,at WalMart,HD,or Lowes.
--
Jim Yanik
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John Willis wrote:
[... snip...]

Wonderful idea! What will you think of next? Bonfire? Congratulations for your fast 'progress' towards the stone age!
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On 1 Nov 2005 16:12:03 -0800, snipped-for-privacy@altavista.com scribbled this interesting note:

You're very welcome!
Personally, I don't throw out old technology. We've had power outages in this area that can last anywhere from less than a minute to several days. In the second case, a kerosene lamp, a gas cook top, and a good ice chest will get you through. The computer will be useless. The TV dead. The corded telephone may or may not work, depending upon conditions, and the roads will be impassable, although the cell phone charger in the car can be used to keep that one working...if the system is up.
You may not know it, but you, Sir, are addressing an individual who owns 78 rpm, LP 33 1/3 RPM, and 45 RPM records, in addition to eight track tapes, cassette tapes, VHS, CDs, CD ROMs, and DVDs. And I can play them all. The oldest playback device I own is a Victrola from the mid-1920s. The latest is a DVD player less than a year old. Just because something is new does not, necessarily, make it better in all circumstances. In that power outage, I could still wind up the old Victrola and listen to a little Bach!:~)
-- John Willis snipped-for-privacy@airmail.net (Remove the Primes before e-mailing me)
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John Willis wrote:

I agree with you that old technologoly has its merits - some of it is even superior to its newer counterpart - and I myself enjoy using it on many occasions. But like everything else, it has its place and time. Let us assume that the advice you gave me is good enough for you to take it yourself. If so, I am amused with the idea that every time when you turn your computer on, you also light your kerosene lamp and keep it burning beside the keyboard until it is time to turn your computer off.
Disappointed as I am with the response which I got in this thread to my inquiry about building a filter, I took it with good humour, amused myself with the various comments (even the uncalled for rebuke by Jim Yanik on Oct 31, 8:50 pm, where he clearly demonstrated that he did not pay sufficient attention to the passage he was quoting), but while I decided not to respond to any of those postings, it was too much for me to hold back my reaction when your idea showed up. O.K., if you are happy with a kerosene lamp burning beside your computer, who am I to object.
As a byproduct to my disappointment, I still got a pay off in two ways. First, a lot of laughter, and laughter, so they say, is good for health. Second, I found here a fellow, namely yourself, who, like me, enjoys classical music. It is nice to meet people with something in common to share.
All the best,
Aharon
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On 6 Nov 2005 14:30:58 -0800, snipped-for-privacy@altavista.com scribbled this interesting note:

Only when there is a power outage does the kerosene lamp get lit!~:) And then, not having a UPS, the computer stays off!:~(

Happy to have been of service!:~)

-- John Willis snipped-for-privacy@airmail.net (Remove the Primes before e-mailing me)
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snipped-for-privacy@altavista.com wrote in

How much light do you NEED,as opposed to "want"? You could use a small array of alkaline battery powered LEDS(not hi-power Luxeon LEDs);they could run off two D cells for the time you need (and a lot longer) to shut down your PC when the house power goes down. Run an array of small white LEDs off a 12V gel cell,and it would last for days,if not weeks.
It sounds like you want to light up an entire room with LED light,not just your PC keyboard.
--
Jim Yanik
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And this is most likely your problem.
A UPS puts out a very dirty signal that will easily destroy the cheap electronics within the LED bulb. If you can find a oscilliscope reading of a normal outlet and one of an average UPS I bet you'd be surprised by the difference.
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snipped-for-privacy@altavista.com writes

I wouldn't actually recommend using the lamp on a UPS, especially a consumer level unit. Their output isn't necessarily going to be the smooth constant voltage sinewave that the lamp is designed to work with.
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Clive Mitchell
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On Sun, 30 Oct 2005, snipped-for-privacy@altavista.com wrote:

It is a common misunderstanding that LEDs produce trivial heat. In fact, they produce quite a bit of heat per lumen. The primary reasons for the misunderstanding are:
1) This heat is emitted to the rear of the junction, not "out the front" in the same direction as the light as is the case with most other light sources, and
2) Most people's only LED experience is with the very small, relatively low output items used as indicator lights on e.g. electronic equipment and dashboards. A great deal more light is required for illumination than for indication.
The backside heat produced by LEDs powerful and numerous enough for illumination is *not* trivial, and it creates two problems: There is the issue of thermal resistance in the materials used to build the lighting device, its housing and surroundings -- this doesn't really differ from the same problem with any other light source, with the exception of the location/direction of the heat. This is throwing obstacles into the development, for instance, of LED vehicle headlamps. Not only is the significant backside heat creating thermal management problems requiring elaborate and expensive solutions (fan-cooled headlamps!) to avoid exceeding temperature limits in the lamp housings themselves, but the lack of *frontside* heat means the lens doesn't defog or thaw when the lamp is turned on. Too much heat in back, not enough in front!
LEDs are also highly temperature sensitive with respect to their output. It's common to see a swing on the order of +60% at -30C to -40% at +40C, relative to nominal output at 20C. Most other light sources in current use are minimally temperature sensitive in this manner, if at all. Filament and arc lights generally don't know or care what the ambient temperature is. Fluorescent lamps tend to have low output at low temperatures (and unreliable starting, in extremely low temperatures), but their internal heat tends to counteract low ambients such that this tendency amounts to little more than extended ramp-up time when started from cold. While thermal direction and management issues are causing problems for headlamp engineers, the temperature sensitivity of LEDs' output makes problems at the other end of the vehicle: How do you design a brake lamp that is guaranteed to be sufficiently intense at 40C when its emitters are producing only 60% of their rated output, while not being overly intense at -40C when the emitters are producing 160% of their rated output? It's not as easy as it sounds.

Unfortunately, it really is your only reliable option.
DS
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On Sun, 30 Oct 2005 20:46:58 GMT, Clive Mitchell

I agree that the heat rise above ambient of 20ma LEDs is minimal, but your blanket statement certainly does not apply to high power LEDs such as any of the Luxeons. These will all overheat if not connected to a proper heat sink.
As for the impact of ambient temperature on LED life, there is published data from the LRC that clearly shows decreased life for even small LEDs when they are operated in a high ambient temperature. Data for low power LEDs was presented at the 2002 IESNA Annual conference but I can't find the paper any more on the LRC Web site. Here is the full reference.
Narendran, N., and L. Deng. 2002. Performance characteristics of light-emitting diodes. IESNA Annual Conference. Technical Papers 157-64. New York, NY: Illuminating Engineering Society of North America.
LRC data for high power LEDs can be found at:
http://www.lrc.rpi.edu/programs/solidstate/completedProjects.asp?IDG
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Vic Roberts
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Most LED lamps use clusters of 5mm LEDs. There are a few Luxeon versions, but I shudder to think what the circuitry is like inside them.
If it's the early Chinese white LEDs, then even using them in a fridge wouldn't make them last longer. :)
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Clive Mitchell
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writes

A one watt Luxeon LED draws 300 ma at ~3.4V,all you need is a 3 terminal regulator IC and a dropping resistor to limit the current,and properly heat-sink the Luxeon LED.(and sufficient overhead on the supply.) Not efficient,but it will work.
In a dark room,a 1W Lux LED is really bright,maybe too bright at close proximity to a keyboard.
IMO,too much,I'd use a few 5mm bright-white LEDs.
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Jim Yanik
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So let's assume you are using a 120V source. That's 120 - the 3.5V for the Luxeon makes a total of 116.5V to drop at 300mA. Better make that a big resistor for the 35W it's going to have to dissipate.
I could always build one for our 240V supply. That would dissipate 71W.
I'm guessing that the commercial Luxeon lamps contain an unregulated switchmode circuit like the circuitry in a CFL.
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Clive Mitchell
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writes

Why not use a plain old iron-core *transformer* (wall-wart?)to lower voltage and boost current AND efficiency? (120VAC source)
IIRC,the OP was talking about driving them from a 5 or 12V DC source. That's what I was responding to.

More likely to be a regulated switchmode circuit. LEDs like a constant current. CFLs are much more tolerant than LEDs.
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Jim Yanik
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LEDs do actually produce as much heat as the same wattage lightbulb. Here's a link http://www.patmullins.com/ledlightmyths.html#toc2 that describes the screw in bulb replacements as doomed to fail without adequate heat dissipating area. I think the Lumileds design guides also show that surface area to be about 9 square inches per watt. Here's another link for a LED lightengine http://intencitylighting.com/IntenCity_OEM.htm with 400 square inches, and the adjoining pages show that to be about 36 watts of LEDs.
Here's another link http://www.enluxled.com/ showing a screw in bulb replacement that actually appears thermally viable.
LEDs with Fins! I'm impressed with that one.
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snipped-for-privacy@tns.net wrote:

The MCPCB that Lumileds stars are mounted on, 1 inch square , is rated as minimum heatsink requirement for 1W in 25 C ambient, temp of star board in 70`s C and junction temp at the limit.
Adam
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Yes, the Lumileds parts with a dissipator will operate at room temperature, but life time is short. For commercial applications, they require a lot more surface area, or a lot of airflow.
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