WOptical communication
WAviation light signals
WFlag semaphore
WFlare gun
WFree-space optical communication
WHeliograph
WHydraulic telegraph
WInternational maritime signal flags
WKoruza (technology)
WLanding lights
WModulating retro-reflector
WOrbital angular momentum multiplexing
WPhotophone
WPulse (signal processing)
WOptical telegraph
WSignal lamp
WSmoke signal
WVisible light communication
WVisual approach slope indicator
WVolta Laboratory and Bureau
WZ flag