[Len Green]

~~ Trumgottist ~~ ... Thanks. Odd... I was pretty sure that it's "I was" and "You were". Is it some special case here (you write "conditional" in paranthesis) or am I simply wrong?

You may be right about that ?!?
I was born, bred, & educated in London (UK) and have written a lot and edited a magazine, but my Degree and 40 years teaching was in Physics and not in the English language.
My English is pretty good, but I am no grammarian! Certain sentences or phrases just SEEM (i.e. sound &/or read) to me to be right, or wrong. Some of these I can back-up objectively, others (including this case) I can’t.
To try to see if I’m correct, I googled http://grammar.ccc.commnet.edu/grammar/conditional.htm
and obtained, amongst other things :-

For present unreal events, we put the verb in the condition clause one step back — into the past, examples:
** If the Bulls won another championship, Roberto would drive into Chicago for the celebration.
** I wish I had tickets.
** If they were available anywhere, I would pay any price for them.
** If he were a good friend, he would buy them for me.
****** Note that wishing is always an unreal condition. Note, too, that the verb to be uses the form were in an unreal condition. More about this in a moment.

I would be pleased if somebody who has a better English grammatical knowledge than me, were to confirm or reject my contention!

I've changed the cook line straight away, but I don't know what to do with the window. Your suggestions don't really feel right. I don't want to call the light friendly, and I can't come up with a good alternative if it's odd to describe a light as warm in English. (My thinking was that a white or blue light is cold while a yellow or red is warm. Is there another word for this in English?) Maybe I should just remove the comment about the light completely, and let Frasse jump up and look inside instead. That would probably make more sense anyway.

No… don’t do that!... The sentence is FINE. The only actual error and anomaly are as pointed out:-
A warm light is flowing out this window. ~~~~ Should be:-
A warm light is shining out of this window.
It is quite common to talk about “the cold light of dawn”, etc. so I suppose it’s perfectly OK to talk about a warm light (certainly “the warm glow of a fire”).
Bottom line :- My suggestion, respectfully is:-
Don’t “just remove the comment about the light completely”, but instead just substitute the line …………….
A warm light is shining out of this window.