Went to google to find out more. The song was composed by Harry Dixon Loes (1895-1965). He was with the Moody Bible Inst. from 1939-retirement.
The original (public domain) is in the CCF Chordbook, www. its.caltech.edu/~chords/chord355.shtml.

The verses given are:

This little light of mine,
I'm gonna let it shine (sing couplet 3 times)
Let it shine, let it shine, let it shine.

Hide it under a bushel, NO!
I'm gonna let it shine, etc.

Won't let Satan blow it out,
I'm gonna let it shine, etc.

Let it shine 'till Jesus comes,
I'm gonna let it shine, etc.

Looks like there are many variations.