what makes sweet basil flower? light, temperature, or combination of both?

Answer 1

The genus Ocimum evolved in the tropical, sub-tropical and warmer parts of the temperate regions of both hemispheres.
Basil requires warmth to grow (50 degrees minimum temperature) and requires heat (80s and 90s) to thrive. Light is less of a critical factor with day length varying less in the near tropics.