Providing your plants with the correct amount of daily light is absolutely critical for healthy growth and development. This fundamental aspect of plant care can literally make or break your harvest success. Think of daily light as your plant's "food budget" – just like we need a certain amount of calories each day, plants need a specific amount of light energy to function properly.
When you transition your plants to a 12/12 lighting schedule (12 hours of light, 12 hours of darkness), you're essentially cutting their daily light exposure in half compared to longer photoperiods. This creates an important challenge that many growers overlook.
To maintain healthy plant growth during shorter light periods, you need to increase the intensity of your lights. This means your DLI will change, and your plants will receive more concentrated light during those 12 hours to make up for the reduced exposure time. It's similar to eating larger meals when you have fewer opportunities to eat throughout the day.
Measures the number of photons in the PAR range (400-700nm) hitting a surface per second. Expressed in μmol/m²/s (micromoles per square meter per second). This tells you the intensity of light at any given moment. Each stage of the plant will require a different PPFD Value. PAR meters are pricey, I recently discovered an easy workaround that significantly reduced my equipment costs. Coco for cannabis has an amazing article on PPFD , as well as testing various popular light brands on their youtube channel. The team at Migro has created an awesome tutorial showing how to use an affordable LUX meter to measure PAR using their simple conversion formula. PAR meter Hack from Migro
The total amount of PAR photons delivered to a surface over a 24-hour period. Expressed in mol/m²/day. DLI = PPFD × photoperiod hours × 0.0036. This is the cumulative light dose plants receive daily. There is a great calculator that will help you find your DLI easy, No science required 😆Visit our DLI calculator Here to use . Giving your plants the correct amount of " Daily Light " is very important. This can make or brake a good harvest. As when you switch to 12/12 lighting , the plants wont have as many hours of light, but a higher level or light for less hours.
Young plants with 1-3 sets of true leaves. Very sensitive to light intensity.
Rapid growth phase focusing on leaves, stems, and root development.
Transition period with stretch growth and initial flower formation.
Peak flowering with maximum light demands for bud development. Mostly these high values are used with additional cO2 source
Light intensity directly affects leaf temperature and tent temps. Higher PPFD requires a dailed in environment. High swings in tempature and relative humidity causes plant stress, especially inside tents & green house. It's good to have hydrometers. One in the lung room, one in the tent to keep a close eye VPD. Use CannabisWise's VPD Calcuator Here
At high PPFD levels above and over 800 μmol/m²/s, plants can benefit from elevated CO2 levels (1000-1500 ppm) to maximize photosynthetic efficiency and prevent light saturation. Exhale Bags are popular for indoor tents and are sold online. Amazon has them for $40.(USD) Make sure to read & follow product directions very carefully. As well as having a cO2 monitor would be a good idea! c02 can be very dangerous / deadly to human beings you are not a plant