An oscillator cannot generate visible light through an antenna because the connecting cable does not transmit at those frequencies, and metal does not allow light to pass through. While radio waves can be transmitted, light behaves differently and cannot be carried by standard cables. The discussion also touches on the concept of photomixing, which involves using two lasers to create oscillations at specific frequencies, potentially in the visible spectrum. However, current applications of photomixing have primarily focused on generating terahertz radiation rather than visible light. The feasibility of using photomixing to produce visible frequencies remains uncertain.