Light intensity during flowering

I do believe I am going to see if I can trigger flowering today. What should I set the light intensity at? Also is everyone pretty much in agreement with 12/12 being the right setting?


12/12 is a go.
I dont change intensity until I see flowers.
But the Photone app can help set DLI


These guys got you covered. Photone and DLI will take all the guesswork out of lighting. Stay with the manufacturer suggested heights and tune intensity to get the right DLI. Adjust intensity up or down a little based on how your plants respond.


I use DLI for the light measurements. When you flip to 12 hours from 18 and leave the light output the same level. The DLI will drop to about 65% of it was at 18 hours. Here is a chart for recommended DLI during different plant stages. And a chart that I made to read the DLI under my HLG Diablo boards, and this one will show the difference in the DLI in 12 vs 18 hours.

1 Like

12/12 a go like the other growmies said.

since your changing schedule i would say it’s a safe bet they’re photos
This chart will be helpful for setting DLI correctly.

And recommended ppfd values

For regular weed growing, the PPFD for seedling stage is 100-300 µMol/m2/S; the PPFD for vegetation stage is 400-600 µMol/m2/S, and the PPFD for flowering stage is 800-1,000 µMol/m2/S.

When the CO2 supplement in weed growing, the PPFD in the seedling stage is 100-300 µMol/m2/S, while the vegetative stage requires 800-1000 µMol/m2/S PPFD and 400-800 ppm CO2. The flowering stage requires 1,000-1,500 µMol/m2/S PPFD and 800-1400 ppm CO2.

My girls are sitting at 1050 µMol/m2/S PPFD and the DLI is at 42ish I’m just now in week 5 of flower.

Hope this helps

Get Growin!


12/12 unless you have something like a Haze Sativa or other equatorial Sativa’s in that case you want 11 on 13 off

OK, a question to midwestGuy and everyone on the board. What is a good light meter that can also measure and or calculate DLI?

Many download the Photone Grow Light Meter to there phone. If you want to spend $$ go to Apogee Instruments. If you watch youtube light reviews many will be using Apogee meters.
Truthfully if you have a light that has published ppfd maps you can get close enough based on distance and the map.
If you plug hours and avg ppfd into the formula you get DLI

DLI = PPFD X light hrs X .0036


I use the Photone app on my iPhone. It works fairly well for the price. It will read in Lux, PPFD, and DLI, and it reads the DLI of my older lights well. But with the Diablo I read the light at the canopy top in Lux, and use the previous posted chart to obtain the correct DLI.

1 Like

Photone app vs apogee meter.