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The Microsoft Kinect uses an IR source (laser or just diode?) to project a pattern in order to get 3D data on what it's looking at. As low-power IR is invisible and intangible, many people have concern about it, implicating it when they feel a sensation in their eyes (e.g. a feeling like eye strain), and some claim to have measured the output to be vastly higher than permitted.

Has the Kinect IR source been soundly implicated to cause any sorts of health problems, or has it been measured to output more than permitted by applicable regulatory bodies?

  • would they sell it in litigation mad America or consumer protection mad Europe if it known not to be safe? They'd be certain to be the target of many extremely expensive lawsuits the moment the first units hit the street. – jwenting Apr 29 '11 at 7:18
  • @jwenting: The trick is to hire a very effective lobbyist to help get the laws changed prior to introducing the product to market. =O Nah, that only ever happens on TV. =D – Randolf Richardson Jun 22 '11 at 5:41
  • would probably be cheaper to change the design, Randolf. Laywer, lobbyists, and bribes (oops, "incentives") are much more expensive than are product engineers. – jwenting Jun 22 '11 at 8:53
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Many factors play into this. Sadly, simple google searches do not get me much data that isn't noise regarding the very question you are asking about. That said, I am a Program Manager working on many varieties of IR lasers, so I will attempt to give you information as best as I can explain it.

First of all, anything people "feel" in their eyes is purely psychosomatic. The retina does not have any pain sensors in it (the linked diagram shows no nerve endings in the eye). Any eyestrain is more than likely from spending hours in front of a TV set playing a video game as opposed to the laser.

The laser itself is 780nm (visible light ending at 760 nm, thus making the Kinect laser very short wave IR, or SWIR). Furthermore, it is not columnated, but rather diffused so that it covers a wide area. The power of the laser ends up at less than 0.4 µW once it actually reaches you, so you have even less reason to worry. It is rated as a Class 1 laser device, which means the maximum emitted power of the laser is <25 μW, spread out over a circle detection area measured in feet as opposed to an aperture of less than 1 cm. This amount of power, according to current medical and physics knowledge, is safe.

For the sake of comparison, sunlight is one kilowatt per square meter and perhaps 5% of that is near infrared i.e. 700 to 1000 nanometers. Just going outside will expose you to much greater power densities of SWIR than the Kinect.

As to the way the Kinect physically generates the laser, the IR laser diode itself is capable of emitting 60 mW at 830 nm. Should you break or remove the diffuser, various optics, and then stare into the laser emitting diode directly, you will cause retinal damage. However, the series of steps required to do that would indicate a willful intent to cause self harm, and be beyond simple mechanical failure.

EDIT TO ADD: As previously stated, in order to be classified as a Class I laser, the emittance must be <25 μW. The reason that the diode generator is higher is because the optics required to create the dispersal pattern reduces the efficiency. Any time a laser passes through any optical element, you lose power. The beam divergence will also play into this. If the M2 (M squared) is close to 1, you will have problems. I have not found any measurement of the Kinect M squared, however, since it is already set to diverge, that optical path is established before it even leaves the device. This ends up reducing the ability of the laser to be focused in any meaningful way on your retina.

I would call into question the methodology that people claim in measuring the power from this laser.

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    Upvoted for an extremely good explanation. – eckza Apr 29 '11 at 15:35
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    @Fabian, the Class I rating has the emission limit of 25 μW, which is still in the safe range (and below what normal solar flux exposes you to). So again, safety devices must be disabled in order to cause damage. So again, any "strain" they feel is more than likely psychosomatic or just a result of playing video games for extended periods. – Larian LeQuella Apr 29 '11 at 17:09
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    In order to be classified as a Class I, the emittance must be <25 μW. The reason that the diode generator is probably higher is because the optics required to create the dispersal pattern reduces the "wall plug" efficiency. Any time a laser passes through any optical element, you lose power. The beam divergence will also play into this. If the M2 (M squared) is close to 1, you will have problems. I have not found any measurement of the Kinect M squared, however, since it is already set to diverge, that optical path is established before it even leaves the device. – Larian LeQuella Apr 29 '11 at 22:04
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    +1 just for providing the context that sunlight power flux in the IR is higher! – matt_black Sep 28 '11 at 13:24
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    @JoelB I see what you did there. :) Actually, it is a fair comparison, because the IR radiation starts to diffuse as soon as it leaves the internal aperture. While you are looking towards the Kinect device, your eyes have an aperture of a few millimeters at a distance away, so it's akin to looking at all that diffused IR energy that the sun pours out all the time, even if you aren't looking at it (just any surface warmed by it). – Larian LeQuella Feb 6 '13 at 2:49
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I just directly measured the Kinect laser's output power, which I posted on Youtube:

http://www.youtube.com/watch?v=7qLDzLYPG-w

The short of it is that the Kinect is a BLINDING HAZARD if you look at the laser from 2 inches away or less. Be very careful of children poking their heads in front of the Kinect while it's on!!

At a distance of one foot and more from the Kinect, the laser's power per area drops to levels lower than ambient lighting, so as long as you don't play absurdly close, there will not be any detrimental health effects.

  • Hm. Interesting. But since your measure seems to contradict the safety label (class I laser) I would like to see some independent verification of this measurement. Also (complete noob here) don’t you have to correct your measurement for ambient light? Some kind of calibration? – Konrad Rudolph May 28 '11 at 13:10
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    -1 self references aren't good enough here. – jwenting Jun 22 '11 at 8:56
  • This demonstrates (without sufficient peer-review, or evidence that there has been no hanky-panky) that the sensor puts out a certain amount of power, but there is a big gap between that and demonstrating it is an actual blinding hazard. – Oddthinking Jun 4 '14 at 15:53

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