At human scale, light seems to
propagate instantly from one point to another nevertheless the speed of
light is not infinite.
This speed is really huge for our human senses and scientifics had been
unable to measure it for a long time.
In emptiness the speed of light has the following approximate value:
300 000 km/s
or 300 000 000 m/s
x 108 m/s
This speed has roughly the same value in the air but is lower in water
( 225 000
km/s ) and in glass ( 200
000 km/s ).
More generally speed of light is lower in transparent mediums than in
emptiness or air.