John 1:4

1:4 In him was life, ¹  and the life was the light of mankind. ² 

John 1:8

1:8 He himself was not the light, but he came to testify ³  about the light.

John 9:5

9:5 As long as I am in the world, I am the light of the world.” ⁴ 

[1:4]  ¹ tn John uses ζωή (zwh) 37 times: 17 times it occurs with αἰώνιος (aiwnios), and in the remaining occurrences outside the prologue it is clear from context that “eternal” life is meant. The two uses in 1:4, if they do not refer to “eternal” life, would be the only exceptions. (Also 1 John uses ζωή 13 times, always of “eternal” life.)

[1:4]  ² tn Or “humanity”; Grk “of men” (but ἄνθρωπος [anqrwpo"] is used in a generic sense here, not restricted to males only, thus “mankind,” “humanity”).

[1:8]  ³ tn Or “to bear witness.”

[9:5]  ⁵ sn Jesus’ statement I am the light of the world connects the present account with 8:12. Here (seen more clearly than at 8:12) it is obvious what the author sees as the significance of Jesus’ statement. “Light” is not a metaphysical definition of the person of Jesus but a description of his effect on the world, forcing everyone in the world to ‘choose up sides’ for or against him (cf. 3:19-21).