How to determine rarer & denser medium for light?

[Laven]

How to determine rarer & denser medium for light?

As i read in one book, it's written that denser medium & rarer medium for doesn't depend upon density.For eg. steam has less density than dry air but the steam is denser medium & dry air is rarer medium for light.Before this i used to think in simple way,substance that have high density is called denser medium & vice-versa.

I even googled about it but i don't get any topic related with it.

Hope you help.
Cheers,

 

[Redbelly98]

Optical density can refer to either the absorption of light or the speed of light (i.e. index of refraction) in the medium. Usually this is clear from the context in a specific situation.

So, a medium has a higher optical density if either it absorbs more light per length of material, or the speed of light is slower -- depending on which usage of optical density is being used.

http://en.wikipedia.org/wiki/Absorbance

 

[Neo_Anderson]

Ibtl!

 

[Laven]

thanks for your suggestion.