Which of the following wireless standards requires line-of-sight in order to operate?
Answer Description
Infrared (IR) light requires line of sight in order to properly function. Infrared is most commonly used in TV remotes. WiFi, Bluetooth and Radio Frequencies (RF) do not requires LoS and can penetrate physical objects such as walls and ceilings.
Wikipedia
Infrared radiation (IR) is electromagnetic radiation (EMR) with longer wavelengths than those of visible light, and is therefore generally invisible to the human eye (although IR at wavelengths up to 1050 nm from specially pulsed lasers can be seen by humans under certain conditions ). It is sometimes called infrared light. IR wavelengths extend from the nominal red edge of the visible spectrum at 700 nanometers (frequency 430 THz), to 1 millimeter (300 GHz) Most of the thermal radiation …
Infrared - Wikipedia, the free encyclopedia