No, not green houses.
As passy777 said, they are Dragon Fruit orchards. I've driven to Phan Thiet from Saigon many times and the orchards are always lit up at night time, with strings of ordinary incandescent bulbs, just like the picture above.
Of course, offshore you will see hundreds of very bright lights (mercury vapour?) on the squid fishing boats. So many that sometimes you think you are flying over land. Each boat has an array of lights down each side. These could be mistaken for green houses, if you weren't aware that they were boats.
Further north, around Da Lat, there are lots of green houses for flowers, but in my experience, the HKG-SIN tracks don't go near Da Lat.
Last edited by India Four Two; 19th Feb 2015 at 07:12.