Lighting is a huge part of commercial cannabis cultivation. Some estimates assign up to 33% of all energy used in an indoor grow to lighting. Additionally, the number of lights you plan to use will determine the size of your grow (commercial grows are often referred to by the number of lights they include, rather than by square footage).
The number of lights you need can vary greatly based on available space and growing method. If you plan to have 4 plants per light in Flower and are aiming for 125 mature plants at a time, you will need 32 lights in the Flower Room. From there, an additional 10-20% of overall lighting should be located in the Veg Rooms and 10% in the Nursery.
Because plants grow as they move from room to room, more plants can fit under each light during earlier growth stages. It is common to have 5-6 plants under each light in the Veg Room and 20-100 plants per light in the Nursery. Using our above example, this would result in a total light count of 64 lights with the following breakdown:
Flower Room: 32 lights
Veg Room: 25 lights
Nursery: 7 lights
These are, of course, very basic numbers which can vary based on your growing and lighting strategy. Always check with your master grower before creating a final lighting plan.
Many lighting strategies exist in commercial cultivation today, among the most popular are Screen of Green (ScrOG) and Sea of Green (SOG).
Sea of Green method (often used in greenhouses) packs a large number of plants under each light. This allows for less plant work per plant in the flower cycle. Smaller yield per plant. More information on SOG.
Screen of Green is a method of training the plant to optimize flower production. Using this method, plants are tied to a screen as they grow, creating more budding sites. This allows for multiple colas per plant. While ScrOG requires a bit of extra work during Flower, yields more product per plant. More information on ScrOG.
However, the above numbers only include horizontal lights located above the plant canopy. We are big fans of including vertical lighting, effectively tripling the plant canopy. In Flower, cannabis plants can be trellised and encouraged to grow laterally on the vertical canopy as well as the top horizontal canopy. This substantially increases the plant canopy by placing it on three sides rather than just one, ultimately leading to more buds per plant.
Every grow room should be designed to maximize all resources used. Lighting is no exception and is often wasted – on the walls or aisles of a grow room. When designing the light set up in a grow, ensure that as much light as possible is actually hitting the plant canopy and not other parts of the room. Light that ends up in aisleways and on walls is wasted light and thus wasted money. Choosing the right reflector for your needs can go a long way towards creating a more efficient commercial cannabis cultivation site.
Update: 2/22/16: The total light count was updated to reflect actual numbers used in the example.