Hanoi has a place in the heart of Vietnam; it gets, on average, 1500-1800 hours of sunshine a year, which equals about four to five hours per day. It varies by season, for consideration in each season. Mountainous and sunny from October to December; anticlimactically, heavy cloudiness and rain move in from May to September.
In Hanoi, the capital city of Vietnam, the summer months (April to September) yield anywhere between 20-30 hours of sunlight in a month, while the winter months (January to March) reveal around 15-20 hours of light in a month. The sunlight is not constant throughout the year because of the local climate; that is, temperature, humidity, and cloud cover are factors playing some blockade role in the sun's rays.
From May to October, during the months of the rainy season, the cloud cover might obscure the sun for most of the day. On these days, the skies can be cloudy, with drizzling and a bit of fog setting in. Although this naturally makes outdoor activities less fun, it does not really alter the number of sunshine hours one can expect every day.