From the brightness of the light of course. If the brightness is increasing it means the the light source is approaching and if the brightness is decreasing it means the light source is leaving.
The expression of genes in an organism can be influenced by the environment, adding the external world in which the organism is or where it develops, as well as the organism's internal world, which includes such factors as its hormones and metabolism.
Chemical properties? raft? 2 different realms my friend
