12.1. Communicating with Infrared Light
The infrared (IR) light used by remote controls has a wavelength close to, but greater than, visible light. Because it's close to visible light, it travels in straight lines and reflects off of surfaces, but it doesn't go through opaque objects. This limits the applications for which IR is useful. It's good for controlling a set-top box, but not so good for opening a garage door, if there's a solid wall between the transmitter and the receiver.
For the most part, the fact that IR is invisible is a good thing. It may be harder to debug something that's invisible, but when you're watching the late-night movie on your new Linux-based DVR, it's nice to know you can turn down the volume without shining visible ...
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