Well it depends if you have access to the hospital you can use a tripod a do a small long exposure to capture that small light around, I would say you can buy a 50mm F1.8 anyway its a cheap lens and great quality also the F1.8 is a good addiction to it.
If you want a F2.8 than you can go to a 24-70 F2.8.
I know this isn’t quite answering your question, but I’d very strongly suggest considering the 70-200f4L. They are going second hand between €400 and €450. Optically, this is an absolutely superb lens.
I had one of these but for the type of photography I do I didnt really need it.
The one thing I found with this lens was it was slow F4 and could not be used with
the 2X converter.
The image quality was great, the sharpness was spot on but I found that I would have
needed the IS.
So if you are going to step up to the L go for the F4 IS or the 2.8 IS if you win on
a scratch card!
But on his case that he is talking about a 70-300 USM the 70-200L F4 would be wonderfull non of them have IS.
I would say the 70-200L is very good but if money is one issue, its hard to say, i have the 70-300 IS USM and it’s pretty decent.
Not a lot of post processing, if you just put all the photos with layers and than use lighten you can see both pictures and so on and so on, but i love this kind of shoots well done ;)