Praise belongs to Allah Who created the heavens and the Earth and appointed DARKNESS AND LIGHT... (Qur'an, 6:1). We all know that without light a person cannot see his surroundings with the naked eye. However, the light that we can see is only a very small part of all light-emitting energy. There are other kinds of light-emitting energy that human beings cannot perceive, such as infra-red, ultra-violet, x-rays and radio waves. Human beings are effectively blind to such light waves. It is interesting, therefore, that the word for "darkness" in the Qur'an is always in the plural.
Note 55. Husaini, Qur'an for Astronomy and Earth Exploration from Space, 175-182.