That's a shame, I only grow under lights indoors and I've never seen anything like that ( brown) on any of my plants.
A fan is constantly on, 3 of them plus the extraction system so there's no chance of a condensation on the leaves even with 60+% humidity. I believe youve managed very well so far just on your balcony, impressive but I noticed in the thread above you're looking at LED's? I don't know very much about lights but there's Migro on YouTube and he has reviewed and tested a lot of LED's, he builds his own brand as well but he is in Dublin Ireland and probably not your nearest supplier. Check out his channel if you haven't already bought a light, or even if you have. I use Lumatek, they are Photontek in the US and Canada. They build pretty neat lights from 100 watt light bars to 1000 watt pro arrays, I am biased, I've a couple of their lights and I think they are the business. They come with a 5 year warranty, and no I don't work for them LOL!
Good air circulation is vital, especially in the dark when there is a rise in humidity.