Durchlaßgradm(the ratio of radiant flux reflected from a surface to that incident upon it); Durchlässigkeitf(the ratio of radiant flux reflected from a surface to that incident upon it); Durchlässigkeitsgradm(the ratio of radiant flux reflected from a surface to that incident upon it); Transmissionsgradm(the ratio of radiant flux reflected from a surface to that incident upon if)