There are fewer daylight hours in the winter. Grow lights provide the full spectrum of light, which helps prolong the hours of light for plants to grow.
I’m a new grower, 17 (on) & 7 (off) is one of the typical “schedules” I highly recommend for grow lights. I assume the purpose of this is to mimic a natural cycle of day and night, but I’ve often wondered what would happen if you grow plants under nonstop sunlight. Is it a poor plan? Thanks!