A user of the LED Museum recently sent these in. This is a Silicon Carbide (SiC) blue LED in a water-clear, 5mm epoxy case. This LED is quite dim, and attempts to boost its brightness by having a very narrow beam, as shown in the photo:
As you can see, this LED has the familiar "square with ring" beam pattern normally associated with high-brightness yellow, orange and red LEDs purchased from Hosfelt Electronics. However, this LED's beam is very weak, probably coming in at just a couple of dozen mcd at best. The ambient light level here is too high for me to get an accurate reading on something this dim. :-(
The spectrum appears to be the same broadband one characteristic of this type of LED. There is emission from red all the way to violet, with a higher peak in the blue region around 450nm. The dominant wavelength (the color your eye would see it) is closer to 485nm, which gives the LED an overall sky-blue color.
The person who sent these says he found them at Halted Specialties Corp. (a specialty/OEM store local to him) for $1.75 apiece.
Goldmine Electronics G9494, $1.29 apiece at last check
This is another example of a silicon carbide (SiC) LED.
This blue LED comes in a T1 3/4 case, tinted a diffused greenish sky-blue color.
When lit, the LED is not very bright at all, especially when viewed from the sides. But it is brighter than you would expect when you look at it head on; they made effective use of the reflective die cup when they manufactured the LED in order to try and compensate for a dimmer than usual chip.
The effective viewing angle of this LED is around 30 degrees or so; beyond that you can probably forget about being able to see it outdoors or in the sun; however it is quite visible in ordinary room light, and would work well as an indicator in household electronics & appliances. I would compare its brightness to some of the original red LED models from the middle and late 1970s; many of which are still in use today.
The color of this specimen is influenced a little by its tinted case, and appears to have less red & orange output than a similar SiC LED in a transparent case would. Overall, it has a color like a pale or light sky blue, but with a hair less red & orange in it (boy that was real scientific, wasn't it?) :)
I'd estimate this one to output about 2-3mcd of light on a good day.
If you can find these cheaply, go ahead and use them in household electronics or portables. But beware, they require around 4.5 volts to light up really well. So forget about using them in your 3-volt Walkman. They'll light at 3 volts, but just barely.
Too dim to project a photographable beam at the calibrated distance of 17 inches, this was taken by holding the LED about three inches from the target. I have a color camera backordered and on the way, this may enable me to capture some better photos of most of the LEDs here in the near future.
Litton (part # unknown, price unknown but suspect under $2 apiece)
If bright LEDs hurt your eyes, than this LED is just what the doctor ordered.
An early, original silicon carbide blue model, it was the first type of blue LED that became available anywhere.
Packaged in a slightly milky, slightly bluish T1 3/4 case, it is essentially barely visible in a bright room. Its light is a pale blue in color and covers a very broad portion of the visible spectrum from red to violet; peaking in the green and high-blue regions. I doubt this model produces even 1mcd of light; rendering it essentially useless for anything but low-ambient panel indicators - there's no way this one will ruin your night vision even when driven at or above maximum ratings.
So you want to make a blue flashlight? Then be prepared to buy about 500 of these - you'll need at least that many of them to get any useful light much farther than a few mm beyond the LED's lens. Instead, buy a single blue Nichia model - it should easily outshine over 500 of these.
The tough silicon carbide chip probably made this one suitable for really tough conditions and areas where ESD might be a problem that would ruin ordinary LEDs though; and they may have also had a home in the cockpits of expensive aircraft at one time or other because of their characteristics. Blue-blocker sunglasses won't make these vanish, because so much of their spectrum falls outside the blue region. If they weren't so dim, they might still be in service today.
As things are now though, they're little more than an unfortunate curiosity - most of them are probably in landfills or are forever consigned to languishing in the bottoms of parts bags and being kicked under workbenches like so much trash.
(If you work in the industry, and know of a few silicon carbide LEDs wasting away in a drawer or a bag somewhere, I'll gladly accept them and promise to give them a good home - please e-mail me if you know of or can obtain any)
Manufacturer uknown; probably Cree. Part # unknown, $15.00 apiece
Back around 1991 or 1992, I bought two of these. One was LOST (how the hell do you lose a $15 LED?!?) and the other was in a piece of equipment which was struck by lightning. The LED in this equipment is burned and blackened on the inside, but amazingly enough, it still lights up!. The light is dim - most of it is being obscured by the burnt epoxy surrounding the silicon carbide die... but it can still be seen in normal room light.
One person seems to think that the bond wire is probably shot to hell, but the LED chip is still getting current from the carbon tracks in the very burnt epoxy surrounding the chip, and is therefore still able to light.
When it was new, it was rated at 5 volts, 50mA and put out 14mcd of light. It was in a clear case, which was ever so slightly tinted a violet blue; presumably so you could tell them apart from other LEDs in your parts bag.
The LED's light was a clear sky blue, almost a greenish-blue cyan color. The LED actually had a pretty broad spectrum, emitting light from the red all the way to near ultraviolet, but about 50% of its light came from the blue part of the spectrum.
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