What type of light source is generally used for transmission rates below 1 Gb/s in multimode optical fiber cabling systems?

The use of LED (Light Emitting Diode) as the light source for transmission rates below 1 Gb/s in multimode optical fiber cabling systems is based on its characteristics that are particularly well-suited for short-distance communication. LEDs provide a broad spectral output, which is beneficial in multimode fiber systems as it allows for multiple modes of light to be transmitted through the fiber, taking advantage of the fiber's ability to support various light paths.

In applications where the transmission distance is relatively short, the lower cost and simpler optical components associated with LEDs make them a practical choice. They generate less power and produce less heat than other light sources, contributing to better long-term reliability. Additionally, for applications such as Local Area Networks (LANs), where the distance and bandwidth requirements are more moderate, LEDs are both effective and economical.

In contrast, other light sources like lasers, while able to provide higher transmission speeds and longer distances, are typically more costly and complex, making them more suitable for applications exceeding 1 Gb/s. As a result, the correct choice here is LED, given that it aligns with both the technical requirements and cost efficiency for multimode fiber applications operating under the 1 Gb/s threshold.