| noslodecoy said: Wouldn't most consumer infrared fall in the near-infrared spectrum? This is why we can "see" it with night vision, at least the cheap consumer night vision which blasts NIR light like a flashlight and then uses a sensor, much like Kinect's sensor, to pick up an image. Also, the IR in a remote just modulates at a frequency, so it just flashes on and off and should operate at a similar wavelength and "appear" as any other infrared light in it's spectrum around 900nm, right? If you are in the dark, with a flashlight, and you shine it on a black t-shirt, you would still see the light reflecting off the shirt. You are certainly right about the hackers and that is one of the reasons I think this guy has it wrong. With everything I've seen, I would think this would have been out by now, especially with such a common material. |
Yes, we'll see, and the piece was obviously overstating possible problems with the tech. Anyway the point was that most other IR devices are led-based, but not laser based. As such the emitter uses a relatively big window of frequencies and the receiver picks them all and locks on the modulation: for an object to be "black" it would have to absorb all of them. Kinect uses a laser, so it's easier that a given material can be very "black" on its narrow frequency spread.
To give a few numbers, if NIR LEDs are similar to the visible light ones, they will have a wavelength width of about 30nm. To have a comparison, in the visible range that would shift you from orange to yellow or from green to blue-green: in other words it's a quite big change, and it's typical for dyes used in clothes to have a much narrower color selection. On the other hand a NIR diode laser has a spread of less than 1nm - in the visible spectrum you would probably not distinguish the colors - and while I have no expertise on spectroscopy of denim (here's a sentence I never expected to write :) ) it is thus more likely to be severely blocked.
