Interesting that the two best London milongas I've been to recently are in the afternoons, which are light at this time of year. Best in terms of general dance quality, general courtesy, and the pleasure of feeling comfortable in fairly crowded rooms.
Another pleasure of these afternoon milongas is that strangers seem to chat with each other much more readily towards the end. I guess that's partly the time of day: by midnight most of us might have other priorities, but at 6pm after a lot of pleasant dances the mind opens out to other people.
So it was that I started chatting with someone I know only by sight. 'Such good dancing!' I said. 'Yes', he replied, 'it was light!' 'It does make a difference, doesn't it?' 'I've seen it myself' he replied. 'People are dancing well, and then the lights get turned down and it all falls apart. I've seen it happen!' & I agree: in fact it's something I've written about from time to time. In the worst milongas the lighting is dramatic, deep shadows, bright patches. It's much more of an effort to stay aware of the couples around you. But worse, as we agreed, there seems to be a loss of inhibitions when the light levels go down. People can't see so clearly, and become more careless. Perhaps they know they are less conspicuous. & we tend to think of dance as abandoning inhibition, letting it all hang out, but dance has to be highly controlled, physically. The formality of the Buenos Aires milongas helps maintain awareness of that control.
Of course there are other considerations. People are less likely to drink when they dance at 3pm: it's more normal to have a glass or two at 10pm. Perhaps the time of day rather than the light level is responsible. But it's true that we are all more alert when the light is good: moreover, bluish light is said to make us more alert, and reddish light to reduce alertness. Perhaps we need tango umpires with light meters! 'Bad light stopped dance.'
Joking aside, I really think it's worth looking at the possibility that upping light levels in milongas can improve the general level of dance. As far as I'm aware shady lighting is a disco/club heritage, and historically it's never been associated with any partner dance. True, some of the Buenos Aires milongas have reduced light levels, but by and large the organisers seem to accept the lighting already there in the halls they use for milongas, with no attempt to make it sexy or dim.