16h+ Light to Vegetate, 12h Light/12h Dark to Flower
Short-day photoperiod plants require 16 or more hours a day of light until they mature enough to produce a good harvest. This period of growth is called "vegetative growth." This period of growth, known as vegetative grown or "veg," only needs to be long enough for plants to get to approximately half their intended size and thickness of leaves.
To induce flowering, short-day plants require exposure to 12-hours of light and 12-hours of darkness evenly. The dark period needs to be completely light-proof. Any light leaks can cause delayed maturation, poor bud quality, and hermaphroditism because it makes plants confused. It helps to think of vegetative and floral growth cycles in terms of the seasons. During vegetative growth, you are mimicking spring and summer where days are long. During floral growth, you are mimicking fall when the shortened day length and less light exposure signals plants to flower and reproduce in preparation for the time when they naturally die and re-seed the next generation. Unlike nature, you'll aim to avoid pollination that leads to seeding in order to trick your plants into producing bigger buds.
Light deprivation systems are used to shorten total cropping time when it is not necessary for plants to stay in vegetative growth until the season changes. Plants can thrive on any type of light that is photosynthetically active, whether it is natural sunlight or light from a grow light. Greenhouse growers may opt to just grow with the natural season, or they can use grow lights and light deprivation systems to grow crops faster and grow all year round. Some growers avoid light/dark cycles by growing autoflowering plants. Autoflowering plants are genetically altered so they flower based on age instead of light/dark cycles.