I would have thought that it would take much longer for water to penetrate a thick epoxy LED case than a thin ELM film.
I routinely put white and pink LEDs in my mouth and I've nver had any problems with my spit killing the phosphor.
I do not answer private messages asking for help because no one else can: benefit from advice I may give or correct me if I'm wrong.
Please ask on the open forum if you have a question and I'll be happy to help, if I know the answer.
I'm sure it does take longer, but AuDuckGuru mentioned they were in the garden. So I'm figuring that means left out in the rain, condensation, possibly quite wet for quite a while.
And most of these higher-power white led's are not in T 1 3/4 cases, they are flat with a thinner layer of some rubbery plastic with the phosphor embedded in it.
Last edited by duffy; 7th February 2009 at 11:37 PM.
My cheap Chinese white LEDs from solar garden lights are the same size as an ordinary LED (T 1 3/4) but they have a fairly flat top so that the viewing angle is very wide, about 140 degrees. They turned into dim blue LEDs only after spending a few days in my hot night light.
A 3rd one was also outside for a couple of years but was never in my hot night light and is still bright white at 23mA. It still has a visible yellow phosphor when it is not lighted.
Uncle $crooge
Be careful when you are looking into that dim blue light, Mr. $crooge.
"White LEDs can also be made by coating near ultraviolet (NUV) emitting LEDs with a mixture of high efficiency europium-based red and blue emitting phosphors plus green emitting copper and aluminum doped zinc sulfide (ZnS:Cu, Al). This is a method analogous to the way fluorescent lamps work. However, the ultraviolet light causes photodegradation to the epoxy resin and many other materials used in LED packaging, causing manufacturing challenges and shorter lifetimes. This method is less efficient than the blue LED with YAG:Ce phosphor, as the Stokes shift is larger and more energy is therefore converted to heat, but yields light with better spectral characteristics, which render color better. Due to the higher radiative output of the ultraviolet LEDs than of the blue ones, both approaches offer comparable brightness. Another concern is that UV light may leak from a malfunctioning light source and cause harm to human eyes or skin."- Wikipedia
I replaced the defective white LEDs with one that sticks out of the case so it doesn't get too hot. It has been lighted for one hour and it is still as bright as it began.
The yellow phosphor on the defective LEDs is gone. Before the chip was covered with phosphor and now I can see the bare chip.
Uncle $crooge
The phosphor's missing? Oh, wait - I know. Firefly larva need to eat phosphor so they can light up at night, see, so...
I haven't seen fireflies for about 47 years.
My new white LED is still glowing brightly after 3 hours. Its top is sticking out of the case and feels quite warm but not hot. The top of the case is so hot that I can touch it for only a couple of seconds.
Uncle $crooge
My new white LED has been running perfectly for over 10 hours so the problem is fixed.
Uncle $crooge
This is the first time i saw a pink LED woow....Originally Posted by Hero999
I've got some in my junk box which I bought for curiosity's sake.
They look like this:
They're just a blue LEDs with a phosphor which makes them pink.
I bought them from Rapid Electronics stock no: 55-1822
Here's the datasheet.
BTW this is ma my first post....
What a great way to start on the forum!
I just cant come up with a good one!
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