Thanks for all the comments on generators. A permanent generator installation would have proper exhaust venting. They can be situated at points to make this more easily achievable. So I do not see this as an issue. The number required to run essential station systems may prove excessive (I have not done a calculation). If the initial electrical design did not include for them it would be harder to build them in later for essential circuits. That said closing a station for the length of time it was must have cost a fortune both in penatly payments and hidden costs to business and the public.
I am a bit baffled by the posts on the dual supplies that were available. My interpretation is that it was not a fully resilient system but that only part of the power required could be met by the supply that was left. If this is true then the arrangement needs reviewing. Of course power equipment could have been damaged at the station preventing full station power but there was no mention of this by anyone as far as I can tell.
Guildford station is in the open not like the fully covered areas of Euston. Guildford could have benefitted from the ambient light from the surrounding street lighting (assuming it was not affected) or just because it was able to take advantage of what natural light was available.
I would be interested to know if on the platforms how much light the trains provided. Was it enough to light the platform so you could see where you were going. I accept the walkways up to the platforms may have been darker. Of course in the war many stations had no lighting at all or very low level lighting. Obviously we are all wimps today