As I'm getting close to switching my plants to flower and having a new light, the Vipar KS5000, I wanted to talk about daily light integral (DLI) and lighting.
We all know PAR is photosynthetic active radiation. DLI is the total amount PAR in a day. The total amount of light they get in a day is more important the how intense the light is. DLI can be a difficult equation but I will give you an easy example. You can use this super easy DLI calculator click
here
750 PAR x 16 hours = 12,000 (DLI 43.2)
1000 PAR x 12 hours = 12,000 (DLI 43.2)
For marijuana our sweet spot is 43.2 DLI. To achieve this we go to our manufacturer's PPFD map and pull as best we can from their results. Always keep a measuring tape handy. I have learned from all my experiences and years of growing using HPS or even blurple leds, the leaves will "taco" or "canoe" up to block the light when they are receiving too much light. If you see that your DLI is way too high.
I will give you my light's map for example. They almost make it fool proof with the provided recommendations. The recommendation for vegetative stage is 28" and 75% power. This gives 600 PPFD in the middle and a little to be desired. So I make a logical choice and hang it 25"-26" to get it closer to 750 PPFD. If the leaves canoe. Back the light off etc.