What determines how far a light can reach from its source in Unity?

The range of a light in Unity specifies the maximum distance that the light will effectively illuminate or affect the scene. This parameter dictates how far away from the light source the illumination will reach, thus directly influencing the visibility of objects and lighting effects in that range. By adjusting the range setting, developers can control the area that the light covers, making it crucial for achieving desired lighting effects in different environments and gameplay scenarios.

While other parameters such as output power, distance, and spread may influence how the light behaves or looks, they do not specifically define the reach of the light from its source. Output power refers to the intensity of the light emitted, distance can be vague as it could suggest various things, and spread involves how the light is distributed or how diffuse it appears. In contrast, range specifically quantifies how far that light will extend into the scene, making it the correct answer to the question.