本文的主要内容有四点.一是对近期本刊发表的《光由光密介质射向光疏介质时半波损失的条件》作补充讨论，给出一些数学公式上的解释和相应的物理情景. 二是讨论该文中谈到的一些关于半波损失的看法，并指出当偏振平行于入射面的光从光密介质入射到光疏介质、且光密介质折射率远大于光疏介质折射率时，一般不会有半波损失. 三是给出薄膜干涉的定量计算结果，展示了在通常情况下，教科书上的薄膜干涉公式结果与按菲涅耳公式计算的结果是非常接近的. 四是指出，教科书上的薄膜干涉公式所指示的暗纹条件恰好是正确的，但对于亮纹条件，在某些情况下，该公式会得出完全错误的结果.

There are four parts in this paper. First, more discussions about the formulas and the physical situations are presented to the article “Condition of half-wave loss when light is emitted from optically denser medium to optically thinner medium”, which was published in this magazine not long ago. Second, some views about half-wave loss in that article are discussed. It is pointed out that there is usually no half-wave loss when the light with polarization parallel to the plane of incidence shooting on the medium with small refractive index from the medium with large refractive index and the ratio between their refractive indexes is huge. Third, the quantitative analysis of the interference of thin film is presented. It is shown that the results from the formulas in the textbook are usually close to the results from the Fresnel formula. Fourth, it is pointed out that the formula of the interference of thin film for the dark lines in the textbook is right, but to the bright lines, it will be absolutely wrong in some cases.