光線

1. Origins, structure, and basic meaning

• Structure: 光線 is read as こうせん and is a noun for a ray or beam of light traveling in a direction.
• Basic usage: A beam drawing a thin line across the floor appears in 光線が細い線を描く, while passing a ray through a prism appears in 光線をプリズムに通す.

2. Common pitfalls and similar expressions

• Subject and experimental object
  • Use が when the beam produces a visible line and を when it is the object passed through a prism.
• Difference from 光
  • Unlike the broad word for light, this term focuses on a directed ray or beam, including an optical path in an experiment.