It depends on the age of your plant Seedlings actually need very little light. The veg light is fine for the first couple of weeks. I switch my plants to full lighting so they have access to the full spectrum available throughout the grow at the end of week 2. While red lighting is especially important for bloom, it is still utilized during vegetative growth as well. After the seedlings are growing for a few weeks turn both the lights on and keep them both on for most of the grow. The first few weeks of flowering your plant will stretch and put on some massive vegetative growth before throwing pistils. The veg light switch is essential for this growth. I keep full lights on until harvest after the first two weeks.