火か面めん

noun

caustic surface

Technical term in optics: the envelope of light rays reflected or refracted by a curved surface, forming a bright curve or surface. Not a common everyday word.

• 火か面めんは、光こう学がく系けいで光ひかりが集あつまる曲きょく面めんを指さす物ぶつ理り用よう語ごです。

  A caustic surface is a physics term for the curved surface where light converges in an optical system.