These two sources of energy are considered in French as strongly incompatible, which is reflected in the French expression - used when things threaten to go wrong - "il y a de l'eau dans le gaz".   

From there it is hence possible to infer that, most probably, something related to the inadequacy of something to something else is shown in the Large Glass.   

And quite probably too, one may assume that Duchamp wants to elaborate about this primary and quite disappointing inadequacy that Lacan meant  when he used to say: "il n'y a pas de rapport sexuel". And the Large Glass may also be interpreted this way.   

But then it is by no way less legitimate to interpret the Large Glass as saying something about the inadequacy of knowledge with regard to reality.   

Since after all, the water fall is also a metaphor of time as it passes, and time has been at the first rank - and from the very beginning to the very end - of Duchamp's fundamental preoccupations. The water fall is an image of what moves the world. And what might ever move the world better than time ?   

And this lightning gas - quite precisely - brings light - as does Lucifer in the best sense of the word. It is a lightning gas, which enables seeing. And certainly it is a fundamental question for a painter to wonder about what enables seeing. Not so many of them raise this question. But Duchamp did it. And in a way, maybe he never did anything else   

And since Duchamp opposed "retinal" painting his entire life long, then this lightning the Large Glass is all about, may by no means be essentially related to anything like the light or the eyes.   

Because he comes after the Impressionists, Duchamp - who is actually a painter - is quite aware of the fact that light and color do not say anything really essential with regard to vision.   
And because we worked so hard - making use of intelligence as well as artifice - trying to make the most complex of our machines see, we know that quite well too.   

A video camera does not see, does not distinguish anything - whereas when creating a ready-made Duchamp does.   
A video camera simply encodes.   

Because he came after the Cubists, Duchamp was born as a painter, from this intuition that when moving a video camera around an object, you may well gather enough information to rebuild almost any aspect of this object, to rebuild it "in 3D" as we now say.   
But when this has been done, however, nothing has yet been seen.    

Duchamp was born as a painter from this strong conviction that vision may only be understood as a movement of the mind.    
 

...Duchamp's fundamental preoccupations... 

This is why the title of postface of Arturo Schwarz's book is "La Pendule de Profil".