RSV:
He was not the light,
but came to bear witness to the light.

NRSV:
He himself was not the light,
but he came to testify to the light.

NEB:
He was not himself the light;
he came to bear witness to the light.

NJB:
He was not the light,
he was to bear witness to the light.

REBrown (Gospel of John, Anchor Bible):
...but only to testify to the light,
for he himself was not the light.

NIV:
He himself was not the light;
he came only as a witness to the light.

KJV:
He was not that Light,
but was sent to bear witness of that Light.

TEV:
He himself was not the light;
he came to tell about the light.

CEV:
John wasn't that light.
He came only to tell about the light.

LB:
He was not that Light,
but was sent to bear witness of that Light.