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those LEDs from mid 1980..

That other thread about LEDs reminded of something I have observed a few days ago.

I was in need for an additional indicator LED to debug someting. Since it is only a temporary thing I picked an old leaded 3mm red LED out of my 'assorted parts' junk box and soldered it right beside another, new red LED.

The old LED must be from the mid 80th and hasn't seen much use. At least I remember having this LED there since almost forever.

Obviously I noticed a brightness difference, but I also noticed something else: the old LED was *really* diffuse. You could not see any of the inner structure. It was just a little glowing red dot while in the new one (which was diffuse as well) you could clearly see the LED chip, the mechanical support and all that stuff. I tuned the two LEDs for equal brightness for a better comparison.

Overall I liked the look of the old LED a lot more. the glow is just more even compared to the new one.

Which leads me to the question: Does anyone has a source or part-number of LEDs which are not super optimized for low current and high light output but for nice and even look?

Best, Nils

Reply to
Nils
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On a sunny day (Thu, 25 Dec 2014 15:35:03 +0100) it happened Nils wrote in :

I have some green LEDs wit ha concave front:

---- ===========| ( ---- Those look OK

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Cannot seem to find where I got those from...

Reply to
Jan Panteltje

PS

I have some green LEDs with a concave front: ---- ===========| ( ---- Those look OK

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Cannot seem to find where I got those from...

Was conrad.nl I am sure, no longer listed, but digikey has them:

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Datasheet:

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Reply to
Jan Panteltje

They're called "diffused" LEDs - a soft light coming from deep within the lens. Frosted is similar but the light appears to come from the surface of the lens.

They're both becoming rare because an SMD under a light pipe is easier for machines to assemble.

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I will not see posts from astraweb, theremailer, dizum, or google 
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Reply to
Kevin McMurtrie

There are "indicator" LEDs, for direct viewing in a panel, and "illuminator" LEDs, for backlighting some kind of diffuse material with a printed legend. There are various versions of the indicator LEDs, with varying levels of diffuseness. You may be able to figure them out by reading the optical dispersion charts that are provided by some manufacturers. Probably the ones with the widest viewing angle will be more diffuse. I am sure that very diffuse LEDs are still available, I use some in projects.

Jon

Reply to
Jon Elson

Real diffuse LEDs are made by putting glass powder into the encapsulant.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
ElectroOptical Innovations LLC 
Optics, Electro-optics, Photonics, Analog Electronics 

160 North State Road #203 
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hobbs at electrooptical dot net 
http://electrooptical.net
Reply to
Phil Hobbs

There is a lot more powdered glass diffuser (and coloured dye) in the old 1980's and earlier LEDs. The greens back then were rather poor.

I have a demo of late 1970's LEDs in series with modern high brightness types with the same current flowing through the same colour shows very clearly how much improvement there has been in luminous efficacy.

The early LEDs used to improve their quantum efficiency remarkably when dipped into LN2 (or die instantly) - I presume the modern strained lattice ones do not although I have never bothered to try it.

You want ones with integral diffusers but the trend has been towards mostly water clear packaging so you may have to look pretty hard.

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Regards, 
Martin Brown
Reply to
Martin Brown

I don't know about 3mm, but we use 5.8 mm (diam) red diffused leds as panel indicators. Manufacturer part number AND114R.

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George H. (Red led's are, "so retro", everyone else uses blue. :^)

Reply to
George Herold 

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I've had very good results with the 2mA. HLMP-4700 family from 
HP/Avago. 

John Fields
Reply to
John Fields

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