Challenges - Disadvantages

Despite all the advantages that Visible Light Communications present, there are some limiting factors in their use. The other side of the coin regarding security of VLC which is based on its directivity and not propagation through walls and intercepting objects is that communication can be established only in case of line of sight (LOS) communication. If an object intercepts the LOS, communication is no more achievable. VLC are also capable of delivering wireless data transfer and high throughputs only for small distances of some meters, maybe up to 10. Electromagnetic waves suffer losses as they propagate in free space (in air for this case) proportional to the square of their wavelength. Visible light has much smaller wavelengths compared to RF thus presenting significantly higher losses. While there are no interferences from other RF sources and negligible from other VLC sources, VLC are prone to sunlight which is the most prominent source of noise – interference. Especially in the daylight when sun is quite strong the SNR (signal to noise ratio) at the receiver could be significantly degraded. Moreover some technological issues that have been under research are also bottlenecks for VLC. For example the small modulation bandwidth of light sources constraints the data rates so techniques like equalization at both transmitters and receivers are employed, LEDs are mostly designed for illumination purposes rather than wireless data transmission, more complex and more efficient modulation schemes must be deployed in order to increase data rates and range and new materials and structures (like organic LED for instance) are under investigation in order to offer the desired properties.

The video below shows a small demonstration of VLC in a LOS regime and what happens when the photodetector exits the light beam.