LEDs have a limited life, and phosphor-based ones it seems more so. Plenty of articles in the solid-state journals about the mechanisms if you're interested, but I don't think there are any easy solutions. Plus they drive them hard in cheap stuff and high temperature/current means shorter life.
Best regards, Spehro Pefhany
Joerg schrieb:
Definitely! I have here a three coin-cells white-LED lamp. VERY Bright!! No resistor or such thing inside!
- Henry
Activated crystal defect growing. The LED goes blind.
- Henry
Jamie wrote in news:YSAcj.35$ snipped-for-privacy@newsfe05.lga:
What green LED has a 3V drop? ISTR that they drop around 1.8-2.2V.
*WHITE* and blue LEDs drop around 3.5V.Joerg wrote in news:lEBcj.2949$ snipped-for-privacy@newssvr19.news.prodigy.net:
probably not more than 25ma. That's the usual for the 5mm white LEDs.
This one doesn't have resistors either. There is a chip under a blob of tar but it's so small that I don't think it is meant to dissipate anything. And it doesn't get hot. The whole lamp runs off three AAA cells and they have two LEDs in series, total of six. The really strange thing is that there is also a reflector and a regular but faily dim bulb in the center. So maybe they want you to have a backup in case it all blows. After all this lamp is meant for crawl spaces and stuff and it would be a real bummer having crawled all the way to the end of the house and then ... poof ... darkness.
Looks like this one:
Dang, I paid $7 or so and now it's on sale for $3.
Hmm, then I wonder about all the stuff around here that has been powered for decades. The LEDs don't seem to have dimmed much. Of course that's not easy to tell over such a long period but those must have over
100,000 hours on the clock. For example the printer LPT mux. Bought it in 1989 for $10, if that. Made in China, no brand name, definitely not top-of-the-line stuff. It's been on since that time except for one month of shipping across the ocean, plus another month for escrow to close. Two red LEDs, as bright as ever.
Actually, ultra-bright green ones do.
Best regards, Spehro Pefhany
Obviously the definition of "long run" will vary. ;-) Your eye has a log response. The same problem occurs with IR LEDs, as many an engineer has discovered.
Best regards, Spehro Pefhany
Sure, if the LED is efficient. The number of mA required is like the number of eggs you need to make an omlette-- one is enough*.
Best regards, Spehro Pefhany
I've got to think heating it would help that. Might not be as good for the diffusion or epoxy around it, though. Depends on the scale of the defects.
Tim
-- Deep Fryer: A very philosophical monk. Website @
Joerg schrieb:
For the price you can get just two ;-)
Mine have indeed 3 cells with one switch and one white LED. Nothing more! A very pleasant stable case. All metall. 3 Euro.
This is not your price. They just want to clear off the store.
- Henry
Joerg schrieb:
No! Humans are very sensitive to am modulation but not for long periods of time. You just can't see it. I saw LEDs running 20 years and they faded out. Barely seen in the dark. Most important is the process technology of the manufacturer. They just bought the lowest price LED. Not correlated to quality in either way :-)
- Henry
Tim Williams schrieb:
The defects are on the atomic scale. Every heating from outside or because of internal loss will force the entropy...
- Henry
On a sunny day (Wed, 26 Dec 2007 17:03:27 -0800) it happened Joerg wrote in :
Ja, Beerenburg, been a while since I tried that, 30%, but it never diffused me :-) The diffused ones (LEDs) that have no colored plastic are OK I think. Th colored ones can look like they are 'on' when sunlight hits those at the right angle. That is why I always try to use non colored plastic. I have one nice example here, rectangular, non-colored, diffuse, in my DVD player.
10 x 3 mm, orange 'standby' light. _ | | | | | | -On a sunny day (27 Dec 2007 02:03:16 GMT) it happened Jim Yanik wrote in :
mm you sound so convincing I just measured it again, 2.989 V at about 2.9 mA.
Read what Don Klipstein writes about InGaAlP green LEDs.
I think it is good to know this, it may make a difference in some designs, I have used LEDs in the past to get 1.5 V stabilized, forget it now :-)
Added a blue one now, that one is 2.8 V at 1 mA (2k2 in series on 5 V).
On a sunny day (Wed, 26 Dec 2007 22:26:58 -0500) it happened Spehro Pefhany wrote in :
Especially ostrich eggs.
That is French, Dutch is: 'ei' (sounds like a bit like 'aye', but more towards 'ee'
There's your "constant-current" source.
robert
But then you also have to schlepp around both of them.
They probably use the internal resistance of coin cells as the limiter.
Probably. I guess the Christmas sales weren't quite as expected everywhere.
Nope, the button clicks through five states and only the last one turns that bulb on.
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