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IR is electromagnetic radiation with longer wavelengths than those of visible light at 0.74 micrometres (µm) to 300 µm, which is extends the nominal red edge of the visible spectrum.

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If infrared light is not visible to the human eye, why do most tv remote controls and security cameras appear to have a visible red colored LED lit when the infrared light is being emitted? Is that … visible red light present as a convenience (introduced by grace of the component designer?) or as a by-product of emitting actual infrared light? Is it possible to have infrared light emitted without this visible red color? …
asked Aug 2 '17 by dtmland