To Shine
To Project, To Extend Outward, To Appear
intransitive verb, godan verb, transitive verb
The kanji is distinction, and the verb version here means… a million things. Let's just focus on a few common meanings. Things with distinction tend to stick out from the others. They tend to shine, you know? And if you imagine shining a beam of light on something, that light tends to project or to extend outward. It sticks out, shines on something, then makes that thing more distinct too.
That's why you can say 光が差す (light shines), かげが差す (a shadow is cast), 指差す (to point at), or even カサを差す (to open and raise an umbrella). Basically, 差す usually has to do with causing something to appear, either by shining or projecting outward.
The reading of the kanji is actually the same as the reading for this word, making things easy (both on'yomi and kun'yomi are さ).
暗い部屋に光が差しています。
Light is shining into the dark room.
よく日が差す部屋に変えてもらえませんか。
Can you change the room to one that has bright sunshine?
窓の外を見ると、もう雨が上がって薄日が差していた。
When I looked outside the window, the rain had already stopped and a soft light was shining through.