Stage 1: Collecting light
Light energy is absorbed by chlorophyll in the leaf.
Stage 2: Light dependent stage
This energy is used to split water into hydrogen and oxygen.
Stage 3: Sugar production
Hydrogen and carbon dioxide are used to form sugars (glucose), while the oxygen is released as a byproduct.
How to Improve
It's the easiest maths in the world:
more leaves + more light + more CO2 = more photosynthesis.
To keep your CO2 level high, aim to replace the air in your grow room around 20 times per hour. Bear in mind that plants can use up to 1,200ppm of CO2. To reach this level, you will need to add CO2 to your grow room.
As for your light, if you've got the space, consider increasing your intensity. Failing that, make sure you replace your lamps and reflectors regularly to keep light output high!
You can also try nipping out.
Nipping the top shoot out diverts hormones and energy into the surrounding side branches and tips, which become stronger and bigger than they would otherwise have been.
This helps create bushier plants with more leaves for photosynthesis and top shoots with multiple flowering sites.