During germination I keep light intensity at about 10,000 lux (luminous flux), once the marijuana plants are transplanted into cups I increase intensity to about 20,000 lux. After about 5 weeks, the plants are once again transplanted into full-sized pots (vegetative growth) and light intensity should be increased to between 40,000 to 50,000 lux.
During flowering (12 hours on/12 hours off) light intensity should be between 60,000 and 80,000 lux at the canopy. Interestingly enough light intensity can’t be too high (even if grow room temperature is fine). If it’s too high (over 90,000 lux) it may cause bleaching of leaves and buds.
As a comparison sunlight has an intensity of around 120,000 lux at its peak, with 20,000 lux in the shade. In terms of measuring light intensity, I’m using LED lights, and so I have to use a light meter that is made especially for measuring LED lights, it’s a more expensive one than the meters used for normal indoor lighting, both use the same units of measurement the LUX, but there are differences in the way they work, so make sure you get the right one for the type for lights that you are using.
- Germination light intensity; 10,000 lux
- Post germination (beer cups); 20,000 lux
- Full sized pots (vegetative growth); around 50,000 lux
- Flowering stage; 60,000 to 80,000 lux
- Too high an intensity (over 90,000 lux) is not good, it may cause leaf and bud bleaching