At a point on a surface. Quotient of the luminous flux incident on an element of the surface containing the point, and the area of that element.是什么意思_At a point on a surface. Quotient of the luminous flux incident on an element of the surface containing the point, and the area of that element.在線(xiàn)翻譯_英語(yǔ)_讀音_用法_例句