The optical density of a transparent medium (material) is an
inverse measure of the speed of light through the medium.
The more optically dense a transparent medium is, the slower
the speed of light travels in that medium.
Reminder: The speed of light in a vacuum is 3 x 108 m/s.
The speed of light in air is very close to the speed
of light in a vacuum.
We assume the speed of light in air is “
” or 3 x 108 m/s.
c