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Why do yellow (amber) & lime green LEDs suck? Answered

In my experience, I have dealt with many colors of LEDs, and from what it seems, red, neon green, and blue LEDs tend to be pretty good at producing light as well as surviving abuse. They also tend to require the least amount of current. However, I have found that almost all the the classic lime green and yellow LEDs are very different, and generally don't give much light output even with significant amounts of current! I have a couple of ultra bright red and blue LEDs at the moment that will glow bright enough to see them easily only a 100 microamps! That is something I simply cannot do with any of the yellow or green LEDs I've ever had!

A bit of research shows that GaN and InGaN is commonly used for the blue and neon green LEDs, while GaAsP, AlGaInP, and GaP are typically used for the old-school red, amber, and lime green LEDs. I imagine brighter and more rugged yellow LEDs must exist, given their use in stop lights and road signs. Do they in fact exist? Or is our yellow LED technology still stuck in the 1980s due to little interest in them and little to no R&D?

The reason I ask is because I want to build a light source utilizing amber and blue LEDs to mimic white light, and I'm purposely trying to select colors which will give a white light w/ extremely low CRI. However I want yellow LEDs that are a closer match to blue LEDs in terms of intensity, and preferably, efficiency.

I did some small scale experiments with some unknown LEDs salvaged from christmas lights, and I am impressed how poorly this light renders colors! (and how quickly my 15 ohm resistor went up in smoke driving all the yellow LEDs I had to use to equal the light from a couple of blue LEDs!) although the light hitting white paper appears purplish white, colored objects seem ghostly and take on either a deep blue, muddy grey, or yellow. Perfect for maybe a haunted house ambient lighting! Add a 50Hz capacitive driver to get some good flicker and presto, worst light quality EVER! :D


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4 years ago

I know the LED problem from my work back in the days on traffic light systems.
When the first LED ones came out I had to take crash case apart just to check these amber LED's.
To my big surprise they were not amber at all!
Like the blue ones there is some phosphorous material added on top of the actual crystal.
Similar to what we know from the 3000k range for LED downlights.
Because I could I contacted our supplier about them to get some more details.
Sadly all I could get was "They are especially designed for our company, there is no retail of them unless you buy at least 10000 directly from the supplier.

Old style amber LED's use a very fragile and sensitive crystal that won't produce much visible light compared to blue or green.
There are now high intensity amber LED's available but as there is little demand in the hobby sector and even less for other applications other than traffic lights or wrning lights they are hard to come by.
I have an old single chip amber LED "laser".
At the time the company classified it as a laser due to the extreme intensity of the light.
Originally it was used in an automated optical control station for reflow soldered circuit boards.
The chip inside is almost 5x5mm in size and as far as I could tell made up of at least a grid of 10x10 amber LED chips of a tiny size.
The brightest I could find in a hurry is about 8000mcd.
This company also stock a great range of Cree LED's in various colors, maybe you want to check what's on offer before giving up ;)


Answer 4 years ago

That's surprising! I am sure I have only dealt with the old school amber/yellow LEDs, and I can tell they are as narrow a wavelength as low pressure sodium visually. :/ It does not have a phosphor "feel."

Mouser only seemed to have reinforced the lack of cheap, bright, amber LEDs, especially ones more in the ~570nm range. (most are the more orange-y 591nm ---- 600nm) I did come across one claiming 22000 MCD, but looking at the datasheet, that's only because it has a very narrow 6 degrees viewing angle! :O

Guess in my design will need 3 times as many amber power LEDs to blue ones, oh well :/