The Light is the generic name given to those who oppose the Dark One. Unlike the Shadow, there is no unified structure and there exists several disparate groups. These groups, such as Aes Sedai and Children of the Light, often oppose each other as strongly as they oppose the Shadow. During the War of the Shadow however, there was such a structure, under the command of the Aes Sedai.
Many sayings invoke the Light
"No one can walk in the shadow so long that they cannot walk in the Light"
“It was only by the Grace of the Light – or else by that Shadow-given gift of making men follow him even to sure and certain death." (About Artur Hawkwing, TWoRJTWoT, Ch. 11)
"Thank the Light I am not him.” (General)
"The Light sear my soul if it does" (Jaim, NS, Ch. 1).
"The Dark One and all the Forsaken are bound in Shayol Ghul, bound by the Creator at the moment of creation. May we shelter safe beneath the Light, in the Creator's hand" (Catchecism)
"Light help us!" (General)