Um raio fino de luz é simplesmente chamado de raio de luz .

There isn't a more specific term for a thin ray of light.

No entanto, dependendo do contexto, você pode usar termos como:

* Light beam: This term is generally used for a more concentrated and focused beam of light.
* Light ray: This term is used in geometric optics to represent the path of light as a straight line.
* Light streak: This term might be used to describe a thin, bright line of light that appears to be moving rapidly.

Ultimately, the most appropriate term depends on the specific situation and what you are trying to describe.