What kind of light stays together in a tight beam of parallel light?

The correct choice, collimated light, refers to light that is packaged in a parallel beam. This means the light waves are traveling in the same direction with minimal spread and divergence. In many applications, such as lasers, collimated light is essential because it allows for focused energy delivery over long distances. The arrangement keeps the light intensity concentrated, which is necessary for procedures requiring precision, such as in medical treatments or optical devices.

In contrast, divergent light refers to light that spreads out from a point source, causing it to lose intensity as it travels. Coherent light refers to light waves that maintain a constant phase relationship, but this does not inherently imply they are parallel or tightly focused. Lastly, diffuse light scatters in many directions, lacking the directivity that characterizes collimated light. Thus, understanding these distinctions highlights why collimated light is significant in various scientific and practical applications.