Depends on how tight the beam is and how high gain on the receiving antenna. For a point of reference: radio transmitter => light source, focused beam => light focused with a lens, antenna gain => strength of lens. If you have any questions, just visualize the system (or draw it out) as a series of light sources and light sensors. RF and light are both radiation and follow the Maxwell equations. (Optics are sometimes considered to have additional properties mostly due to limitations in our current understanding of certain RF spectrums, see terahertz bandgap but by and large they follow the same rules).