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I've seen some warnings regarding IR sensors and transmitters such as the 4th panel below for the Nintendo 3DS:

enter image description here

The Operations Manual says,

Do not get too close to the infrared transceiver
Looking directly into the infrared transceiver can lead to impaired vision and other problems.

But if IR is lower frequency than visible light how can it be bad for your eyes? What are the possible adverse effects of looking straight into an IR transmiter?

  • Can anyone access the relevant safety standard text? EN62479:2010 – Sklivvz Sep 2 '14 at 8:50
  • @Sklivvz I feel it should be a medical-science tagged question – shortstheory Sep 2 '14 at 8:59
  • It seems a bit of a stretch in my opinion - environmental-health is more precise – Sklivvz Sep 2 '14 at 9:02
  • X-rays and microwaves are also outside of human sight. I still would not stick my eyes in a microwave. Here is an interesting link with a lot of data ilo.org/oshenc/part-vi/radiation-non-ionizing/item/… (cached: google.ca/…). Which does point out that the main point of damage is eyes. – Jonathon Sep 9 '14 at 1:34
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    I'll leave this as a comment because it is not a full answer but there is a misconception here - that frequency determines radiation strength or dangerous radiation level. Microwave is much lower frequency compared to visible light. Yet exposure to microwave cooks flesh while exposure to a very bright spotlight barely warms your skin. When it comes to your eyes, it's the intensity that matters (measured in lumens for visible light or Watts in general). Visible or not, an stream of photons that's intense enough will damage your eyes. – slebetman Nov 5 '14 at 8:07
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Take a look at the spectrum for sunlight. About half of the energy emitted by the sun is infrared (see citation 6). Some of this is attenuated by the atmosphere, but approx. 30% of the 1000 watts of sunlight power that reach sea level are in the infrared spectrum.

IRDA systems use IR leds such as this one. These have emission spectra in the 900-1000nm range (completely covered in the ir emission spectra of sunlight), and output powers <<1 Watt. (The one pictured above has a max power of 0.075 watts).

Therefore, going outside on a bright day will deliver >3000 times more infrared energy in the same spectrum to your eyes than an IRDA port.

  • I don't see how this answers the question. The question is "Is X dangerous?", how is saying "Y is 3000 more dangerous" answering the question? – Federico Sep 13 '17 at 12:34
  • The general idea is that if you get far more from everyday activity, then it is unlikely for the smaller amount to be dangerous. That argument is often made in relation to radiation. Of course, eyes have mechanisms to restrict the amount of visible light that enters. It's possible that they don't protect from IR. So a smaller amount of IR light might be more dangerous. – Brythan Sep 13 '17 at 13:52
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Quick answer: it's harmless. Maximum radiation dose is 20 times smaller than the safety limit.

Long version: Well it all depends on several factors:

  • spectral characteristic of IR source,
  • beam shape,
  • spatial energy density (energy distribution)
  • exposure time
  • temporal characteristic (continuous/impulse)
  • current eye adaptation state (number of opened rods/cones)

Calculating it is not an easy task, even for the professional (you can find ISO standard, which is under code 10110 if I'm not mistaken, however you'd need to pay an access fee).

Generally speaking, you could assume that typical devices with output power under 20mW are safe to look at for several seconds if the beam diameter is above 2mm. It might partially blind you (glare effect for visible spectrum and NIR) and maybe cause minor, insignificant damage. Below is how well are different wavelengths (IR is above 950nm) detected by human eye:

EDIT:

http://www.dtic.mil/dtic/tr/fulltext/u2/663246.pdf

http://www.dtic.mil/dtic/tr/fulltext/u2/663246.pdf

You can find necessary standards here (most importantly ISO 11254-2): https://www.iso.org/obp/ui/#iso:std:iso:10110:-17:ed-1:v1:en

Simplified calculations Assuming classical IrDA diode like: http://www.excelitas.com/downloads/DTS_CR50IRDA.pdf

and typical eye (pupil and focal length) with ideal optical transmission case (no power loss in air and eyeball) as well as ideal transformation:

enter image description here

[ https://en.wikipedia.org/wiki/Geometrical_optics ]

We have a set of variables: - pupil diameter: 7mm (average) - eye lens focal length: 18mm - eye diameter: 24mm - lighting angle: 160 deg - IR light power: 20mW - wavelength: 870nm

Assuming that you touch the IrDA port to your eye, the distance between light source and eye would be 5mm, then, using the above equation with given data, the light limited by 7mm pupil will focus 7 mm behind lens, so basic geometric analysis gives as spot diameter on retina equal to (24-7)7/7 = 17mm. At 5mm distance, diode irradiates total field of pi*(5mm / cos(160/2 deg )^2=830pi mm^2 but only pi*(7mm/2)^2 = pi*12.5 mm^2 is transmitted through eye pupil.

Concluding: your retina would be exposed to 1,5% of 20mW power on 900 mm^2 surface of retina which is 3 * 10^(-4) W over 9 cm^2 = 3,3 * 10^(-5) W/cm^2 where the laser standard (more restrictive) for wavelength of 900nm is 7 * 10^(-4), so it is 20 times smaller than the safety limit.

[ according to "Safety with Lasers and Other Optical Sources: A Comprehensive Handbook" by D. H. Sliney, J. Mellerio ]

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    Welcome to Skeptics.SE! Have a look at the link here for answering questions with authentic references-skeptics.stackexchange.com/help/answering and please add references for your calculations, factors etc. – pericles316 Mar 12 '16 at 11:44
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    Here is additional information for answering here: Welcome to Skeptics! Please provide some references to support your claims. – Larian LeQuella Mar 12 '16 at 17:22
  • Sorry, for that. I was in hurry while writing this answer. I've updated it with some references and sample calculations. – Rev Mar 14 '16 at 0:43
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Here is a brief description of why IR can be dangerous.

Despite not being visible, IR rays can still pass through the anterior structures of the eye and reach the retina. Since you are unable to detect IR, there will not be any blink or aversion reflex to protect your eyes from damage.

Getting too close and staring into an IR transmitter is effectively the same as getting too close and staring into a flashlight - the mechanism of injury is the same.

The actual standards for IR protection can be found here.

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    I see light (my eyes are even open to any infrared radiation) all day and every day. Is there any reason to say that the Nintendo device emits dangerous quantities or dangerous concentrations of IR, or any other reason (e.g. legal reason) why the warning should appear in the Nintendo instructions. – ChrisW Nov 11 '14 at 18:26
  • I don't know, but I suspect including it in the manual was due to this being an exceptionally litigious society. Lawsuits regarding the absence of warning labels are pretty common: Google 'The True Stella Awards'. – Chance Nov 11 '14 at 19:04
  • I don't now whether the question is trivially easy to answer (i.e. "can IR damage eyes?"), or whether it's Nintendo-specific and more difficult to answer (i.e. "can IR from Nintendo transmitter damage eyes?"). – ChrisW Nov 11 '14 at 19:09
  • We had essentially this answer before (well, not as well stated, but the same content) and this one has the same problem: you haven't given the slightest bit of evidence that any consumer device emits dangerous intensities. – dmckee Nov 12 '14 at 3:40

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