- A. 1, 2 and 3 only
- B. 1, 2 and 4 only
- C. 1, 3 and 4 only
- D. 2, 3 and 4 only
Answer: C
Explanation
The signals in the 380-780 nm wavelength interval of the electromagnetic spectrum are the light signals that can be detected by the human eye. It is possible to achieve illumination and data transfer simultaneously by means of LEDs that is the prominent lighting equipment lately. By this way, both interior lighting of a room and data transfer will be achieved without the need of an additional communication system. This technology is given the name of Visual Light Communication. Hence statement 1 is correct. Technological advances allow to modulate the light at higher frequencies, allowing richer information. Light can be transmitted across a free space (e.g., lasers communicating between two buildings) or across a medium (e.g., fiber optics). With the advent of LED, a new idea in VLC is to use general lighting to communicate with users in a space as a replacement or supplement to Wi-Fi. While traditional light sources present practical limitations, LED lighting can be modulated at very high frequencies, with a cycle as short as nanoseconds. This concept, called Li-Fi, could be a solution to RF bandwidth limitations as the visible light spectrum is 10,000 larger than the radio spectrum. As a bonus, VLC doesn’t cause electromagnetic interference. Hence statement 4 is correct. The light can transmit information either directly or reflected from a surface. It can do so while dimmed. However, light cannot penetrate obstacles such as walls. Thus for wireless communication purposes VLC cannot be used for long-distances. Hence statement 2 is not correct. While Bluetooth transmits data at the rate of 300kbps (kilobytes per second), VLC can transmit data in the range between mbps-gbps (megabytes per second to gigabytes per second). Hence statement 3 is correct.