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Comment by 0_____0 | Hacker News Reader

Is it just a bunch of IR LEDs? Surface mount or through-hole? What's the module power rating? What's the power supply power rating? Are there any secondary optics like lenses over the LEDs? Is there a diffuser of some kind?

If it's a cluster of garden variety through-hole LEDs with domed tops (like you would see on a TV remote), they're necessarily low power on account of having poor thermal performance.

Another way to tell is if nothing gets warm at all. It's pretty hard to hurt someone with an emitter that both doesn't have a focusing optic and doesn't get warm.

Let me be clear - you're still responsible for verifying the safety of your stuff, and I am in no way assuring you that the device you have is benign, because I can't do that without inspecting it directly.

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Yeah, let's say something like this: https://www.instructables.com/DIY-IR-Infrared-Illuminator-Ni...

> Let me be clear - you're still responsible for verifying the safety of your stuff

Obviously yeah. I was just wondering if there were known rules like "these wavelengths under this power are fine for humans and wildlife, even if they put the LEDs right in front of their eyes", and also if you have an array of such IR LEDs, how they cumulate.

And curious about things like: if I don't see it, can it hurt my retina?

I probably will never do it: I wouldn't want to blind a fox just because I wanted to make my own wildlife camera :).

Invisible wavelengths can absolutely hurt your retina, but as wavelengths go farther beyond visible, your eye begins to not focus them properly on the retina, so the risks change. E.g. with 1550nm IR (common in telecom, sometimes in LIDAR) the risk of eye damage is to the surface of the eye rather than to the retina. Short wavelengths like UV will be absorbed by the lens at near-UV, and then eventually just be absorbed at the surface at shorter wavelengths.

I think it would be a cool exercise to figure out how much optical power you would see at, idk, 5cm from your illuminator. I assume it's a shortwave IR close to visible light, so you can assume it will focus like visible light, more or less.

Ideally you'd use an optical power meter but you could get a first pass by looking at the circuit and seeing how many mW pass through each LED, applying a conservatively high efficiency factor of W_optical/W_electrical, projecting that into a radiated cone for each LED and multiplying the power received on a dilated pupil sized spot at 5cm by the number of emitters.

Then you have to work out what the irradiance at the retina is once the light is focused. The hazard criteria include a time factor, so you'll have to decide if you/foxes would like to stare directly into the beam for 10 seconds? Or for the entire duration of your meditation session.

Very interesting, thanks a lot!

I assume CCTV surveillance cameras are usually fine because people cannot go and stare at it from very close then :-).

i went down a rabbit hole doing max permissible exposure calcs for the light you linked and basically i personally wouldn't worry about it. the energy is low and distributed among many emitters. by the time you're far enough away from the light to focus on it, you're receiving max a couple hundred microwatts/cm^2 at the cornea from each led.

I don't know if you ever write blog posts or anything like that, but I would love to see explanations about how you made those estimations. I honestly wouldn't know how to even start :-).

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