Which communication method utilizes line of sight and operates in the infrared spectrum?

The communication method that utilizes line of sight and operates in the infrared spectrum is indeed Infrared Data (IrDA). This technology is designed to transmit data using infrared light, which requires a clear and unobstructed path between the transmitting and receiving devices. This characteristic is why IrDA is often utilized for short-range communication, typically within a few feet.

Additionally, the infrared spectrum is effective for point-to-point communication, allowing devices such as remote controls, computers, and mobile devices to exchange data directly when aligned properly, enhancing security as the signal cannot penetrate obstacles easily.

In contrast, other technologies like Bluetooth and Wi-Fi Direct operate using radio frequencies that do not require a direct line of sight and can transmit through barriers like walls. RFID also relies on radio frequencies rather than infrared for communication and can function at various distances without needing direct visibility between the tags and the readers. Thus, the ability of IrDA to operate exclusively within the infrared spectrum under specific conditions makes it distinct among the options provided.