Cheap ebay 365nm LEDs - Page 1
Forum section: electronics / general

author: Buriedcode
author_rank: Super Contributor
timestamp: September 13, 2023, 06:16:32 am
content: Hi,I have a load of 395/400nm that I got years ago for making an expsoure box but never got around to it, and whilst they do a good job of making stuff fluoresce, the rather bright purple can wash out the more subtle glows of things like tonic.So on a whim and out of curiosity I bought some very cheap 1W UV LED's, listed as being 365nm. It's always a gamble but for £2.10 for 2 delivered I was curious as to whether these really were 365nm.Well, I tested them at a much lower current (50mA, then 100mA) as they are apparently rated for 700mA. And they emit a faint white - slightly yellowish glow that I was kind of expecting for this wavelength, but the output doesn't seem to cause flourescence in any of the usual suspects: highlighter pens, marks on bank notes, UV reactive acrylics - even printer paper which will glow very bright with UV doesn't really glow.So I'm somewhat confused - I would accept that they just aren't UV, but they're far too dim to be anything else. Using a tube blacklight - that is so wide band it makes everything glow - I shone that on the LED to check for any kind of phosphor coating that some modern LED's have - just incase they were mislabelled and were some kind of phosphor LED, but no glow, so they definately have a bare die.They also have the kind of weird glow I have seem from other mid UVA sources.The only thing I can think of is that the lenses they have used are blocking much of the actual UV - preventing them from actually stimulating flourescent materials - whilst letting through the faint off-spectrum glow. That or they're lower than 365nm (doubtful).Unless 365nm just doesn't make many things glow as well as 395?The end goal here to have something a bit less power hungry and more direcitonal than the tube blacklight - but one that doesn't really emit much visible light. I suppose the next thing to try would be an actual 365nm flashlight that are all on amazon/ebay.Here's the kind I got:https://www.ebay.co.uk/itm/235034903272?mkcid=16&mkevt=1&mkrid=711-127632-2357-0&ssspo=gpe_tz_5S3q&sssrc=2047675&ssuid=haCVYFDCS46&widget_ver=artemis&media=COPY

author: Someone
author_rank: Super Contributor
timestamp: September 13, 2023, 07:55:09 am
content: Quote from: Buriedcode on September 13, 2023, 06:16:32 amYes. Excitation spectra can be complex and peaky just like emission spectra, 365nm is often a minima for excitation. Should see a reasonable fluorescence emission from premium white paper (try business cards).

author: jpanhalt
author_rank: Super Contributor
timestamp: September 13, 2023, 08:06:03 am
content: Calcofluor white is/was used as a whitener for shirts and a lot of other things. Its excitation max is about 350 nm. If you have a starched white shirt, does it glow blue-white?Here one use that shows an excitation and emission spectrum:https://pdfs.semanticscholar.org/1cba/a27a3c9e59e6320b5d2d24048dd05bd5af65.pdf

author: Zero999
author_rank: Super Contributor
timestamp: September 13, 2023, 11:31:56 am
content: Quote from: Buriedcode on September 13, 2023, 06:16:32 amTry a higher current. Some LEDs, especially UV don't work well at low currents.

author: MK14
author_rank: Super Contributor
timestamp: September 13, 2023, 11:42:29 am
content: Quote from: Buriedcode on September 13, 2023, 06:16:32 amFollowing your link and assuming the prices haven't been changed, between now and when you bought them.Only the 395nm versions are around £2.10 for 2, delivered.The 365nm, seem to cost a lot more (perhaps twice, or four times the price, before delivery).Those selection menus, can be horrible, and can be readily changed./flipped, possibly unnoticed, when you change other parameters. Such as quantities and things.I.e. They can be VERY confusing.It DOES seem to stick to the type you want, but if you messed around (to save money etc, or if they didn't stock everything at the time you bought them), it could easily have been changed to other types.

author: Buriedcode
author_rank: Super Contributor
timestamp: September 13, 2023, 06:16:01 pm
content: Quote from: MK14 on September 13, 2023, 11:42:29 amYeah they can be quite cheeky with their pricing for multiple options, but I had these in my watch list and they sent an offer of £2.10 for the 365nm ones. At that price I couldn't resist just to see what they sent me.They're definately not the same output as the 395/400nm 3mm/5mm generic ones I have from years ago.Quote from: Zero999 on September 13, 2023, 11:31:56 amAhh yes I will try this. My quick test was just with 3 AA's I had and a 10R resistor - I'll do some proper tests with regulated currents tonight. I guess it could be that as current increases the UV output increases more than the "faint glow" meaning the targets fluorescence will be much more noticable at higher currents and less washed out.Quote from: Someone on September 13, 2023, 07:55:09 amThats interesting. I'll draw up a list of items I have about and google their excitation spectra - as I said, some things "sort of" glowed but nothing compared to the 395's I had. It wasn't a fair comparison as the 395/400s were in an array of 8 with 20 degree emission, also as LEDs are generally narrrow bandwidth its also unfair for me to compare these to the 4W tube blacklight which pretty much covers all UVA.Cheers folks. As I said, it was more of a curiosity purchase and another one of the many "science projects" I have on the go. We're kind of spoiled these days with what you can get cheap. If I do get one of those "dark beam" torches that allegedly has a filter on the output to block much of the visible emission I'll post some tests on here.

author: thm_w
author_rank: Super Contributor
timestamp: September 14, 2023, 12:04:53 am
content: I have the 380-385nm version of these:https://www.aliexpress.com/item/1005004669397698.html($1.50)and a 367nm from digikey ($6 + $1 for the star PCB)On a surface with two white materials, drive current 200mA:- the 380nm will fluoresce very brightly, and in the non-fluorescing material there is a light white/purplish glow (maybe 1/20th the brightness or something)- the 367nm will fluoresce very brightly as well, and no visible light I see outside of that.You can find lots of photos in the ali reviews above.I wouldn't mess around with the lowest tier stuff when the above are only ~$2.