Tiny IR receivers come in 3 versions

What does LCD stand for?
A display technology that uses rod-shaped molecules (that flow like liquid and bend light. Unenergized, the crystals direct light through two polarizing filters, showing a natural background color. When energized, the crystals redirect the light to be absorbed in one of the polarizers, causing the dark appearance of crossed polarizers to show. The contrast and viewing angle improve as the molecules are twisted further.

What is IR radiation?
Infrared (IR) radiation is an electromagnetic radiation of a wavelength longer than that of visible light, but shorter than that of radio waves (between 750nm and 1mm). Applications include target acquisition and tracking by the military, remote temperature sensing, short-ranged wireless communication, spectroscopy, and weather forecasting.