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Sounds harmless to try at home.

Anybody know how to make a 670nm deep red light?

Can an iPhone do it or would you want to buy an LED?

Don't use a light source without some filter that ensures the spectrum is restricted if you really plan to expose your eyes. I would still recommend not doing that without medical oversight. Spectroscopes are expensive, so you probably don't have one lying around, but it is the only way to make sure you don't have peaks in non-visible light that can damage your eyes.

edit: I don't know any light source that peaks at that wavelength, so you would probably use a broad spectrum alternative and a filter to achieve what you want.

Be very careful with this. Light sources can emit all kind of peaks of light you might not notice. For example a LED might look red but can also emit some infrared.

UV is the one to worry about, fortunately it's easy to filter, for example most clear safety plastic glasses don't let it through.

Could that be harmful to the eye?

Yes, just like looking at an eclipse without the proper gear. Your eyes don't register the threat and stay wide open while getting blasted by harmful wavelengths

Would that somehow be different, for 3 minutes, than being outside in sunlight for an hour? Are you maybe thinking of ultraviolet light?

It can be different yes. As far as I know, wavelengths that you don't perceive will not cause your pupils to contract in response to harmful intensity of light.

While it can be very bright in the open sun, your eyes will compensate for this. A light source which emits harmful amount of IR and little to no visible light will probably not elicit this reaction and damage your eyes without you realizing until it's too late.

Infrared lasers are particularly dangerous for this aspect.

This is also how you get snowblindness on cloudy days. The light intensity isn't high enough to cause your pupils to dilate the same way as on a sunny day, and the snow reflects a bunch of UV into your eyes. So you get a sunburn on your retina.

Yes but the reason I pose my question is that the topic is red LEDs, not IR LEDs nor laser diodes, and there's nothing in this article suggesting that for some odd reason you must stare directly into the light source as opposed to looking at a diffusor.

I insist that the "OP" is mostly being alarmist without thinking about all the 620-700 nm (and deeper infrared) exposure we perceive throughout every day.

Have you considered taking a look at e.g. mouser.com, or a specialized LED retailer like led1.de, and just filtering specifically for 670nm LEDs?

In the "LED Bulbs and Modules" categories at Mouser, there are no 670 nm LEDs.

In the "LED Indication - Discrete" category at Digi-Key, there are no 670 nm LEDs. (Digi-Key lets you filter on both peak and dominant wavelength. I assume peak is what we want here but it doesn't matter because there are no 670 nm dominant in those categories either).

In the category "LED Emitters" Mouser does list 670 nm in the filter, but checking out a few of those it seems they all actually specify peak wavelength is 650-670 nm.

I probably just missed it because I don't read German, but at led1.de I could not figure out how to filter on wavelength.

Assuming one is just looking for some through hole LEDs to whip something up on a breadboard, it looks like the closest readily available inexpensive LEDs are 660 nm peak and 638 nm dominant at around $0.40. Typical example [1] which is $0.41 for one, $2.95 for 10.

Since the article said 650-1000 nm, if we assume a peak of 700 nm works, then there are a lot of options, such as [2]. Dominant 635 nm. $0.29, 10 for $2.14.

[1] https://www.digikey.com/product-detail/en/lite-on-inc/LTL-42...

[2] https://www.digikey.com/product-detail/en/kingbright/WP3A8HD...

The closest I could easily find in the UK is this rather dubious looking website: https://www.funkylighting.com/deep-red-led-flashlight-torch-...

Still, if it doesn't help my eyes it'll be useful for my paranormal investigations ;)

An iPhone will not produce 670nm narrow band light.

Here are measured spectra for iPhone X and iPad Air 2 respectively:

    http://www.displaymate.com/Spectra_41a.html
    http://www.displaymate.com/Spectra_35.html

As you can see, although there is some energy at 670nm, there is much more energy at shorter wavelengths (~620-630nm peak) from the screen's red emitter. You can't change the red emitter's spectrum (the rightmost peak in those charts), you can only change the relative height of the three peaks to change perceived colour.

So you can't make a spectrum containing a single peak around 670nm.

Just a note, you are indenting your urls making HN use code formatting on them, thus rendering them not clickable. just paste the url itself without indent.

Noted, thanks. I think they look better in code formatting, but forgot about clickability.

I wouldn't try anything like this until proven. Staring at light doesn't sound harmless to me.

Reminds me of Don't look into laser with remaining eye.

Still, we do it constantly: Any monitor/screen is just a "lightbulb", that we are staring into day to day.

I don't know why you assume you must stare directly into the light source for this to work, compared to for example diffusing the light to a comfortable level with a transparent screen, or pointing a strong light at your bedroom ceiling etc.

Why assume that someone attempting this themselves won't stare directly into the light source. Without specific advise, be cautious of the worse case this might cause.

Buy a deep red LED. Check out GembaRed, or talk to the owner, about where to buy.

I wonder if he'd share where to buy LED that undercut his $160 small LED panels...

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