Lens refractive index ne mafi girma, da bakin ciki ruwan tabarau, mafi girma da yawa, taurin kuma mafi alhẽri, a akasin wannan, da ƙananan refractive index, da thicker da ruwan tabarau, da karami da yawa, taurin ne ma matalauta, general gilashin high taurin. don haka ma'anar refractive gabaɗaya a kusan 1.7, kuma taurin fim ɗin guduro ya fi talauci, maƙasudin raɗaɗi yana da ƙasa kaɗan, guntun guduro a kasuwa a halin yanzu shine mafi yawan ma'anar refractive na 1.499 ko makamancin haka, Dan kadan mafi kyawun sigar ultra-bakin ciki, wanda ke da ma'anar refractive na kusan 1.56 kuma ana amfani dashi mafi yawa.