When your crops are in the middle to late growth phase, some seasoned gardeners advise adding an extra hour of UV light each day.
Then, as your plants begin to flower, provide them with additional UV light for 60 to 90 minutes during the early stages of flowering and for 90 to 120 minutes during the middle of the flowering period.
Increase the additional UV light to 120 minutes as the flowering stage draws to a close, often in the last two to three weeks. As a result, your cannabis may produce more THC and other chemicals as a result of this.
But bear in mind that different plant species respond to UV radiation in different ways, so as you extend the UV exposure, keep a watch on your plants.