Which energy types are primarily used in semi-active homing systems?

Semi-active homing systems primarily utilize the energy types of laser and radar. In these systems, the missile or projectile relies on an external source to illuminate the target. For radar-guided systems, a radar signal is reflected off the target, allowing the missile to home in on it. This type of guidance requires a radar system on the launching platform (like an aircraft or ship) to track the target and illuminate it throughout the missile's flight.

In the case of laser-guided systems, the target is illuminated by a laser beam, and the missile is built to detect the reflected laser light to guide itself to the target. This semi-active approach contrasts with fully active systems, where the missile has its own radar/laser source, and with terminal guidance systems, which might incorporate infrared energy sources for final targeting.

Other energy types, such as infrared and acoustic, are more associated with different types of guidance systems (e.g., infrared homing missiles track heat signatures). Radio waves and visible light don't correspond to the primary functioning principles of semi-active homing as effectively as laser and radar do. Thus, the correct understanding of semi-active homing systems falls squarely within the domains of laser and radar technologies.