Don't humans and other warm objects also radiate IR?

That is far-IR, thermal stuff, Near-IR, 700 nanometer-ish is right below red in human vision.

Camera sensors can pick up a little near-IR so they have have a filter to block it. If that filter was removed and a filter to block visable light was used in place you would have a camera that can only see non-visable light. Poorly, the camera was not engineered to operate in this bandwidth, but it might be good enough for a mask. A mask that does not interfere with any visible colors.

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fc417fc802 2 days ago | parent | next [-]

> Poorly, the camera was not engineered to operate in this bandwidth

At least for cheap sensors in phones and security cameras that engineering consists of installing an IR filter. They pick it up just fine but we often don't want them to.

Keep in mind that sensors are inherently monochrome. They use multiple input pixels per output pixel with various filters in order to determine information about color.

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throwway120385 2 days ago | parent | prev [-]

You can actually dimly perceive near-IR LEDs -- they'll glow slightly red in darkness.

	▲	adrian_b 2 days ago \| parent \| next [-]
		That depends on how "near" they are. The sensitivity to red light decreases quickly at wavelengths greater than 650 nm, but light can still be perceived if it is strong enough, up to around 780 nm. Many so-called near-IR LEDs may actually be somewhere around 750 nm, so they are still visible on a dark background, even if they are perceived as extremely dim. On the other hand, there are many near infrared LEDs around 900 nm and those are really invisible. Near-infrared LEDs around 1300 nm or around 1550 nm are also completely invisible. An invisible near-infrared laser beam could become visible due to double-photon absorption, but if a beam of such intensity as to cause double-photon absorption hits your retina, there are more serious things to worry about.
	▲	diacritical 2 days ago \| parent \| prev [-]
		I remember reading some people can perceive some near IR, but mostly that near-IR LEDs actually leak some red themselves due to imperfections in manufacturing or something?