White LED question - Page 1
Forum section: electronics / beginners

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 11:15:32 am
content: I know that the blue LED first appeared in the mid 90s, but is that the only way to produce white light? I believe most white LEDs use a white phosphor, charged by a UV source, so why didn't white LEDs appear much earlier, before the blue LED?I've come to expect in this forum that someone will imply that I am stupid for asking this question. You will be blocked/ignored.

author: Ian.M
author_rank: Super Contributor
timestamp: August 08, 2025, 11:24:43 am
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amBecause although Nichita had a UV LED back in 1992, it was only 1mW optical output. High brightness, reasonably efficient UV LEDs didn't hit the market till 2002 (although i believe there were far Violet near-UV ones before that), and were initially horribly expensive, so tri-color phosphors similar to those used in fluorescent tubes (which down-convert UV-C from the mercury vapor discharge) weren't viable for LEDs earlier. I bought a UV-A LED circa 2010 to make a UV torch and even then it wasn't cheap compared to white or blue LEDs of similar power.Block me if you like, but do us all a favor and do a bit of research before asking them to avoid criticism of your questions!

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 11:27:22 am
content: Quote from: Ian.M on August 08, 2025, 11:24:43 amThat's probably true, but any such white LED must have been more efficient than an incandescent. The first white LED I ever saw appeared in the late 90s.

author: Ian.M
author_rank: Super Contributor
timestamp: August 08, 2025, 11:46:15 am
content: And your point is?Nichita marketed white LEDs based on Nakamura's blue LED + a Ce:YAG phosphor from 1996. High brightness UV LEDs that could excite a tri-phosphor mix came much later. IIRC they were initially about $15 each for a 5mm 30mA LED.There was a massive obvious market demand for high output blue LEDs even back in the early '90's so that's where the development money went. UV LEDs were much much more niche, and gas discharge UV sources met the market needs of the time adequately.

author: Terry Bites
author_rank: Super Contributor
timestamp: August 08, 2025, 11:48:26 am
content: Ian M is right, and its pertinent advice for everyone on the blog. Do your research, learn how to use google. Dont jump to conclusions.www.energy.gov/eere/ssl/led-basicsI found this in less than 10s!You could go the the inventor's website for the history. Did you check on who invented the blue and the white LED?www.led-professional.com/all/25th-anniversary-of-the-white-led-2013-nichia2019s-innovation"In 1993 Nichia commercialized the very first high luminous blue LEDs.With these high luminous blue LEDs and its then 30+ years of phosphor expertise and history, Nichia created a revolutionary technology.In September of 1996, Nichia combined Yttrium Aluminum Garnet (YAG) phosphor with its innovative blue LEDs to officially produce the first ever white LEDs. "Easy.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2025, 12:14:31 pm
content: Actually the first white LEDs weren't any more efficient than old incandescent lamp. They did last for longer and produced a more stable colour light than incandescent lamps, so were adopted earlier in battery powered applications, but it took a decade fro them to be a feasible alternative to incandescent and longer to replace fluorescent lamps.

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 12:20:56 pm
content: Yep, just what I expected; zero courtesy, fault-finding is the goal.I've done a lot of research; how much is sufficient, is anyone's opinion.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2025, 12:25:49 pm
content: Quote from: Connecteur on August 08, 2025, 12:20:56 pmYou might get a better response if you had posted links/references/citations to your research.

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 12:26:49 pm
content: Quote from: Zero999 on August 08, 2025, 12:25:49 pmI asked a question. What links/citations do you have in mind?

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 12:27:59 pm
content: This has always been a bad tempered group. Nothing has changed.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2025, 12:33:13 pm
content: Here we go again, another Connecteur 'tell me I am stupid' threadQuote from: Connecteur on August 08, 2025, 11:15:32 amI'm sure I must have offended you in some previous thread over the years. Please block me, such offers don't come up every day.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2025, 12:42:47 pm
content: Quote from: Connecteur on August 08, 2025, 12:26:49 pmYou said.Quote from: Connecteur on August 08, 2025, 12:20:56 pmGiven you've done your own research and still have a question, then it would make it easier for us to help you, if you told us what research you've done.Why do you find that controversial?

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 12:43:11 pm
content: Quote from: Gyro on August 08, 2025, 12:33:13 pmMy thoughts exactly.

author: Gyro
author_rank: Super Contributor
timestamp: August 08, 2025, 12:44:39 pm
content: Quote from: Connecteur on August 08, 2025, 12:43:11 pmYou're supposed to have blocked me!

author: Connecteur
author_rank: Frequent Contributor
timestamp: August 08, 2025, 12:59:05 pm
content: Quote from: Gyro on August 08, 2025, 12:44:39 pmNot worth the effort.

author: Ian.M
author_rank: Super Contributor
timestamp: August 08, 2025, 01:03:12 pm
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amThe majority of the white LED market is still (as of 2023) using wide spectrum yellow or bi-color phosphors driven by a blue LED, with a proportion of the unconverted blue light forming a component of their white light output.Quote from: Connecteur on August 08, 2025, 11:15:32 amDo I have to taunt you properly (à la Monty Python) before you block me?"It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so!"Frequently and incorrectly attributed to Mark Twain, probably a rephrasing of "I honestly beleave it iz better tew know nothing than two know what ain’t so." Josh Billings, 1874)

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2025, 01:23:38 pm
content: Quote from: Ian.M on August 08, 2025, 01:03:12 pmI can understand why some think that. Fluorescent tubes use UV and a phosphor and some modern white LEDs do, although with the latter, it's always UVA or more commonly violet, which is said to produce whiter whites because it stimulates fluorescent materials such as laundry whitening agents.

author: bostonman
author_rank: Super Contributor
timestamp: August 08, 2025, 02:06:05 pm
content: QuoteQuoteI'm just curious, why would you ask a reasonably decent question in order to advance your knowledge, indirectly insult all the contributors on here in the start of your thread, and finish your question by inviting criticism?I've posted numerous questions on here and never got a response that implied I was stupid. Many on here take time to answer questions for complete strangers in various countries. If you're offended by the choice of words they use to answer/explain something, then my suggestion is: don't ask a question.As the saying goes: it is better to remain silent and be thought a fool than to speak and remove all doubt.Thanks for speaking to usYou can block me also if you'd like.

author: SteveThackery
author_rank: Super Contributor
timestamp: August 08, 2025, 04:45:34 pm
content: Quote from: bostonman on August 08, 2025, 02:06:05 pmYep, and me. Although I don't recall ever being rude to you. However, when you open a thread in the way you did, it seems like you are expecting to see rudeness wherever you look. Probably not a good place to start from.

author: MK14
author_rank: Super Contributor
timestamp: August 08, 2025, 04:52:39 pm
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amCan I ask a couple of stupid questions?How many user accounts, have you got on this forum?

author: tooki
author_rank: Super Contributor
timestamp: August 08, 2025, 05:06:31 pm
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amFor many years I have searched, in complete vain, for even one single verifiable example of a commercially-available UV-driven white LED. Without exception, every one I’ve looked at, even ones that looked promising, were pumped by blue LEDs. The literature often mentions UV-pumped LEDs, but I am now very doubtful that they have ever been produced outside the lab.The entire white LED industry is optimized around the 450nm blue LED: the phosphors are optimized for that, and on the other side the LED dice are optimized for those phosphors. UV LEDs remain appreciably less efficient than blue ones, and cost more.So with your base premise debunked, perhaps you’d like to revise your question?As for the question as asked: Is the UV-pumped LED the only way to make white light? No. Excluding all the non-LED sources of white light (incandescent, fluorescent, flame, etc), you can use RGB LEDs or blue-pumped phosphors to make white light. Only the latter is used for lighting, but RGB white is common in color LED displays (video walls, etc), some LCD backlights, and color-changing lighting.

author: TimFox
author_rank: Super Contributor
timestamp: August 08, 2025, 05:25:20 pm
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amName one such device (UV LED exciting white phosphor) commercially available.The blue LED was considered to be a big-deal invention when it was new, seehttps://www.nobelprize.org/prizes/physics/2014/press-release/UV LEDs exist, mainly used to replace Hg-vapor sources in UV applications such as curing.Old-style fluorescent bulbs used Hg-vapor UV excitation because it was available, but that created a waste disposal problem.

author: Siwastaja
author_rank: Super Contributor
timestamp: August 08, 2025, 06:57:33 pm
content: Quote from: Connecteur on August 08, 2025, 11:15:32 amBecause there were no UV LEDs before blue LEDs either. (Anything even remotely efficient.)Blue and near-UV (405nm or so) LEDs that had efficiency surpassing incandescent bulbs both came late 1990's or so, and became widespread and affordable in mid 2000's or so.UVC LEDs (close to what mercury-based fluorescents internally produce) are much more recent thing, andstillboth very inefficient and expensive in year 2025; those are not used in white LEDs because of that.

author: Analog Kid
author_rank: Super Contributor
timestamp: August 08, 2025, 07:24:45 pm
content: Quote from: Connecteur on August 08, 2025, 12:27:59 pmMon ami, you obviously have quite le chip on le shoulder here.If you come in expecting to be abused, well, that just might happen.BTW, your original question here wasn't stupid at all. You're just being hypersensitive.

author: Zero999
author_rank: Super Contributor
timestamp: August 08, 2025, 09:46:54 pm
content: Quote from: tooki on August 08, 2025, 05:06:31 pmThat's the norm, but I've seen white LEDs with violet pumped phosphors.These appear to be 425nm.https://www.mouser.co.uk/datasheet/2/423/VAOL-S6WR4-1064919.pdfI also remember a reports of street lights turning violet as the phosphor burnt out.Of course that doesn't detract from your point. I'm just providing more information.

author: RJSV
author_rank: Super Contributor
timestamp: August 09, 2025, 06:43:47 am
content: As to the whole courtesy / blocking things:BOTH sides have valid points, but my advice is, that it's best to (at least) give folks the benefit of the doubt; that they are sincerely trying but occasionally lapse in extending friendly attitudes (like myself included, in lapses).It's a good, but sometimes raucous crowd. I liked the question, and eagerly read the responses, even tho maybe I could have searched out the material myself. The experts responding do it so much better, than my fumbling searches !

author: Gyro
author_rank: Super Contributor
timestamp: August 09, 2025, 08:15:01 am
content: Quote from: Zero999 on August 08, 2025, 09:46:54 pmI see that as a potential problem with the future adoption of UVC dies in White LEDs, assuming they become cheap enough. It would take some really resilient phosphors to resist sunburn in close contact with the die. I know florescent tubes have used such phosphors for decades, but at a vastly lower energy density.

author: Zero999
author_rank: Super Contributor
timestamp: August 09, 2025, 09:55:10 am
content: Quote from: Gyro on August 09, 2025, 08:15:01 amWhy would anyone use a UVC LED to pump a visible white phosphor?As well as photodegradation, it would be horribly inefficient. When a phosphor is excited by a high energy photon, it releases a lower energy photon. The difference between the two energy levels is converted to heat. This is known as Stokes shift. Theoretically it's possible to design a phosphor which takes a releases two lower energy photons, for every high energy photon, but I'm not aware of any substances which exist and if they do, they're not practical and only exist in the lab.

author: tooki
author_rank: Super Contributor
timestamp: August 09, 2025, 10:05:39 am
content: Quote from: Zero999 on August 08, 2025, 09:46:54 pmNice catch! I’ve never actually heard any claims of violet-pumped white LEDs.I’m still looking for evidence of any UV-pumped LED, of course.Quote from: Zero999 on August 08, 2025, 09:46:54 pmHaving seen such failed and failing street lights in person: they’re just failing to 450nm blue. They appear violet when the phosphors haven’t failed 100% and are still emitting a tiny bit of red and yellow.