The first come back from a JW will be " Ah, but don't forget the Light gets brighter". Or similar. It may be good then to show them C.T Russell's words about this :
'As we look backward we can see that our pathway has been as "a shining
light...shining more and more." It has been progressive, bringing us
strength with "meat in due season." It has caused us to grow both in
grace and knowledge and this growth, taken in connection with the fact that we
are not obliged to look back and now call darkness what was then called by some
of the brethren, "a great flood of light," is the very strongest
grounds for confidence that the same Lord who then supplied us light from the
word, is still providing of the same kind. We say then, "cast not away
your confidence" in our Leader, "the great shepherd of the
'If we were following a man undoubtedly it would be different with us; undoubtedly one human idea would contradict another and that which was light one or two or six years ago would be regarded as darkness now: But with God there is no variableness, neither shadow of turning, and so it is with truth; any knowledge or light coming from God must be like its author. A new view of truth never can contradict a former truth. "New light" never extinguishes older "light," but adds to it. If you were lighting up a building containing seven gas jets you would not extinguish one every time you lighted another, but would add one light to another and they would be in harmony and thus give increase of light: So is it with the light of truth; the true increase is by adding to, not by substituting one for another.'
February 1881 Zion's Watchtower page 3:
Of course they may claim this is old light after all it is from 1881!