Older white LEDs (ca. 2005-2010?) had a distinct purple tinge while modern ones have a spectrum much closer to a blackbody. I rather like the look of the older style and would like to purchase some now. Does anyone know what keywords to use to find the older style in a parametric search?
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1\$\begingroup\$ Sounds strange. Spectra of modern white LEDs are quite far from black body, and don't seem to have improved since 200x. There's still the large spike of blue and a dip in cyan on most white LED lamps. \$\endgroup\$– RuslanSep 7, 2020 at 10:48
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2 Answers
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These are called "Full Conversion White LEDs" though by the early two thousands they were partial conversion so you want to look for "Partial Conversion White LEDs". They worked by producing a UV light that excited a phosphorus layer that produced the white light. Some of the purple light from the UV would seep through and cause a purple tint. Also try looking up "Phosphor Film Conversion LED".
Here is an article that talks about them and their history: https://hackaday.com/2018/10/29/history-of-white-leds/
Here is a more technical article discussing it: https://www.digikey.com/en/articles/phosphor-film-conversion-for-white-leds
To be more specific the full name would be "Phosphor conversion indium gallium nitride white LED" sometimes called InGaN, the phosphor used is called yttrium aluminum garnet or YAG. Here is a picture of it:
You can buy them here (notice the blue hue in the picture):
Note: The "Cool White" modern LEDs mentioned in the other answer do not have a color spectrum that looks anything like first-gen partial conversion LEDs. Cool white will still come across as white, though towards the blue part of the spectrum. But the InGaN with YAG phosphor will actually look as though it has a distinct bluish color with a strong blue peak in its color spectrum that exceeds that of modern Cool White LED.
answered Sep 6, 2020 at 10:18
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\$\begingroup\$ That looks like exactly what I'm looking for. A search for "InGaN" on Mouser brought up these; the spectrum (p. 4) has a very strong peak at 465 nm (blue-violet). \$\endgroup\$ Sep 6, 2020 at 10:37
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\$\begingroup\$ @AlexHajnal Awesome,yea says in the Datasheet those are InGaN as well, that should be what your looking for. Dont forget to accept my answer please. \$\endgroup\$ Sep 6, 2020 at 10:39
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\$\begingroup\$ @AlexHajnal by the way the link I provided to buy some also show a picture and they are specifically from 2011 according to the data sheet. So I felt it was a closer match to what you were looking for.. Either should work though, but the older ones had a stronger purple hue, so you may want to go with my link.. either way, please remember to accept the answer and good luck. \$\endgroup\$ Sep 6, 2020 at 10:41
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1\$\begingroup\$ This totally answers my question but I'll wait the customary 24-hours before accepting the answer. Thanks! \$\endgroup\$ Sep 6, 2020 at 10:48
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\$\begingroup\$ @AlexHajnal Sounds good, happy to help. \$\endgroup\$ Sep 6, 2020 at 10:49
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Whilst the exact LEDs may not be readily available due to changes in manufacturing, modern white LEDs (and LED light fixtures) will often be called "warm white" for a more yellowy colour which mimics incandescent light or "cool white" which is more blueish like these older LEDs. So if you choose a "cool white" LED, that will give what you're looking for.
To make this more exact, manufacturers will specify a colour temperature. See this link for a more complete illustration of colour temperature and how it affects lighting.
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\$\begingroup\$ Not sure why this got downvoted. Some LEDs even come with a "color temperature" column in the datasheet, sometimes the range is as wide as 3000-27000K. \$\endgroup\$ Sep 7, 2020 at 11:02
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3\$\begingroup\$ @DmitryGrigoryev Not sure why this got downvoted. Probably because the question was specifically about older white LEDs with a distinct purple tint caused from the UV spectrum used in those, and not just some LEDs with yellow tint trying to mimic warm light from classical light bulbs, essentially making this answer sort of irrelevant. Just a wild guess, though. \$\endgroup\$– Num LockSep 7, 2020 at 11:27
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\$\begingroup\$ @NumLock The relevant part is that such LEDs (or functionally similar ones) are called "cool white" novadays. \$\endgroup\$ Sep 7, 2020 at 11:46
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\$\begingroup\$ @NumLock If you're looking for something similar to older LEDs though, then the colour temperature is exactly what you're looking for. I'll add a sentence to that first paragraph if you don't think it's clear enough. \$\endgroup\$– GrahamSep 7, 2020 at 11:53
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2\$\begingroup\$ @Graham To give you some specific numbers in terms of "Optical Power" modern Cool White LEDs Have a 0.75 relative optical power on its warm peak (the part caused by the phosophor) at 552.5 nM and its blue peak is 1.0 at 452.5. If you compare that to the InGaN w/YAG old school LEDs they have a at the same point of 552.5 also with 1.0 relative optical power, but its warm peak is at 550nM (slightly cooler) and only has a relative optical power of 0.4. So no a modern Cool White is not even remotely close to these older LEDs, the moderns have a 87% higher warm component from their phosphor. \$\endgroup\$ Sep 7, 2020 at 12:39