Confused about pricing: "UV" leds

[Moriambar]

Hi,
I'm starting a project featuring blacklight-sensitive ink, and I wanted to buy some "UV" leds (which I know are mostly violet leds) so I went to digikey and found this, which was the second less-expensive one (the least expensive is not the best for my needs). They cost ~0.53€ in 100 qty.

Then I find this which advertise 350mcd uv leds for these LEDs and also have nice reviews, and they cost only 14€.

How is it possible? it's almost a 4 to 1price difference. Am I missing something?

Cheers

[ebastler]

You are looking at two different products. The one from Digikey comes with a datasheet, probably longer-term availability and stock at Digikey, and possibly even some level of quality control. (At least Digikey will have vetted the supplier before they started distributing their products.) The offer via Amazon is from some independent seller, who presumably sells whatever he could get on the spot market.

Hence, it seems clear that they won't cost the same. Whether the additional peace of mind provided by Digikey is worth the extra cost to you is your decision and judgement call, of course: For use in a one-off hobby project, the worst thing that could happen if you go with the cheap option is 14 Euros down the drain, and quite a few hours of your spare time. For use in a commercial product, the potential impact on customer satisfaction, warranty costs etc. will change the equation.

With either option, be sure to keep safety in mind! There is enough UV in the LED spectrum to damage your eyes during testing and later use. Please take appropriate precautions, design a light-tight enclosure with a proper interlock switch etc.!

[Zero999]

With either option, be sure to keep safety in mind! There is enough UV in the LED spectrum to damage your eyes during testing and later use. Please take appropriate precautions, design a light-tight enclosure with a proper interlock switch etc.!

Well I wouldn't worry too much about safety with a 405nm violet LED, with an optical power output of under 50mW. No need for any interlocks, your eyes receive a higher dose of violet on a sunny day, just don't state at the beam. The health warnings are just to cover the manufacturer's back, in case someone does something silly such as shine the beam directly in their eyes, at close range for half an hour.

The higher powered LEDs, which output an order of magnitude more power, at a shorter wavelength <400nm are the ones which do actually present a safety hazard, but even then they're fairly benign, until you get into the UVB and UVC wavelengths.

Hi,
I'm starting a project featuring blacklight-sensitive ink, and I wanted to buy some "UV" leds (which I know are mostly violet leds) so I went to digikey and found this, which was the second less-expensive one (the least expensive is not the best for my needs). They cost ~0.53€ in 100 qty.

Then I find this which advertise 350mcd uv leds for these LEDs and also have nice reviews, and they cost only 14€.

How is it possible? it's almost a 4 to 1price difference. Am I missing something?

Cheers

Either will do. If the 390nm is genuine, it's probably better, since it will be less visible so the ink will appear brighter.

The mcd rating of deep blue/violet/UV LEDs is BS, since it's scaled to the sensitivity of the human eye, which is fairly insensitive to these wavelengths. What's more important is the optical power output. Ideally you want as low mcd rating, with high optical power, i.e. short wavelength, so it's not visible but enough power to excite the phosphor, so it shines brightly.

Yes Digi-Key do have a large mark-up, which can be bypassed by ebay, but there's a greater risk of fakes: take your pick.

[Psi]

I've seen people use 405nm laser pointers as a cheap easy way to cure UV ink.

You can also get UV nail polish curing units for quite cheap and they are full of UV leds for curing UV nail polish.

[ebastler]

Well I wouldn't worry too much about safety with a 405nm violet LED, with an optical power output of under 50mW. No need for any interlocks, your eyes receive a higher dose of violet on a sunny day, just don't state at the beam. The health warnings are just to cover the manufacturer's back, in case someone does something silly such as shine the beam directly in their eyes, at close range for half an hour.

You are probably right that an interlocked enclosure is not a must at that wavelength. And it would probably defeat the purpose anyway; I assume the fluorescent ink is meant to be looked at?

I am not sure about the total power Moriambar intends to use, however. Based on the purchase quantity of 100 LEDs, I assume it is significantly more than 50 mW, and the idea is to deploy many LEDs to illuminate a large area? In that case, I would suggest to at least arrange the LED in an enclosure or frame in a way that prevents observers from directly looking into the LEDs. (Including small children who observe from below!)

Also, apply the fluorescent ink to a dark background, which does not scatter but absorb most of the UV. That is probably desirable anyway, since it will make the fluorescent colors stand out more. And don't make the whole thing to interesting/appealing, so people don't look at it forever! 

[Moriambar]

Well I wouldn't worry too much about safety with a 405nm violet LED, with an optical power output of under 50mW. No need for any interlocks, your eyes receive a higher dose of violet on a sunny day, just don't state at the beam. The health warnings are just to cover the manufacturer's back, in case someone does something silly such as shine the beam directly in their eyes, at close range for half an hour.

You are probably right that an interlocked enclosure is not a must at that wavelength. And it would probably defeat the purpose anyway; I assume the fluorescent ink is meant to be looked at?

I am not sure about the total power Moriambar intends to use, however. Based on the purchase quantity of 100 LEDs, I assume it is significantly more than 50 mW, and the idea is to deploy many LEDs to illuminate a large area? In that case, I would suggest to at least arrange the LED in an enclosure or frame in a way that prevents observers from directly looking into the LEDs. (Including small children who observe from below!)

Also, apply the fluorescent ink to a dark background, which does not scatter but absorb most of the UV. That is probably desirable anyway, since it will make the fluorescent colors stand out more. And don't make the whole thing to interesting/appealing, so people don't look at it forever! 

Hi, Actually I need 100 led to light 3-6 of them at a time at most with around 20mA each. they are behind a piece of paper and, possibly, a clear polycarbonate plastic sheet (4mm) which should block much of the residual uv light (in theory) while keeping the special ink visible.

Anyway thanks for all of your insights

[Zero999]

It's probably safer than the type of black-light found in a nightclub. They output a few watts in the UVA range. A 4ft unit will output 8.8W, with a peak wavelength of 354nm, see data sheet linked below!
https://controllux.com/downloads/webshop/GEN-16501007/ge-uv-tl-buis-t8.pdf

Granted, LEDs are more direct and less diffuse than fluorescent tubes, but 5mm violet/UVA LEDs are nothing to worry about safety-wise.