From this point, we follow our protagonist as he finds different sighted people using different methods of trying to save themselves. Some try to save the blind, as well. It's a study of how effective different methods of post-apocalyptic managing are. The book shows us each minuscule society and how many end. One of the amusing ongoing bits in the book was how many Brits expected Americans to come save them -- they just had to hold out until the US planes got there. But triffids were worldwide and we were almost certainly in similar straits.
The book was published in 1951, four years before I was born, and the language and mores didn't bother me and I just muttered at the misogyny. One of the big things that bothered me was that the society that seemed most likely to survive (I vote the human race died out, they didn't have enough diversity) was setting up with polygamy. Now, Watson & Crick didn't discover DNA until 1953, but humans had been breeding plants and animals for millennia. You can't have the three women just have the one man's children. Each woman has to have every child by a different man in order to get enough diversity.
Wyndham was very careful to make it clear that the triffids and the green lights were Earth-based phenomena -- Soviet commie triffids and a falling satellite with some kind of nerve gas -- but it makes a lot more sense for both to be alien, from the giant triffid ship that picked us for the next farm and moved on. I can see that he wanted to show us the options for just Earth, but it makes a much too coincidental coincidence.
Something that is almost never included in books like this are people like me. My meds will run out, I can't walk very far or work very much, but I would probably see (I watch most sky stuff on TV so I don't have to haul a chair out and down the ramp so I can sit and look up without falling). So do they take me along to teach people how to do things? A number of the groups were primarily intellectuals and many of them didn't know how to do things like plow and set up pumps, etc. I know how to do a lot of useful stuff I can't actually do anymore. Or maybe I'm just as useless as most of the blind people. It makes the story less black and white, but I'd like to see it explored more. There are a lot of disabled folk.
It's a pretty good book for being 57 years old, and Ghu knows, we've had tons of jokes from it*, so even though I question some of it, I'd still recommend it primarily to see how you react to the different societies. Most of our group didn't like it.
*Years ago at a Balticon, an elevator broke with the doors open. The hotel people were worried that people would get in, push buttons, not go anywhere and get mad, so they put a large potted plant in front of the door. We made triffid jokes for the rest of the con.