Plants use photosynthesis to synthesise carbon from the air into plant tissue. Limiting factors are light, water, nutrient, temperature, ambient humidity and CO2 content in the air. Not the numbers of plants.
Like I said earlier, average yield should be 0.5g-1.5g per 1KW of light. If you prefer imperial measure this is 1.10 to 3.3 pounds per 1KW. If you use more plants it means you can flower them earlier/smaller so more crop per years. If you use only one plant you get less crop per years.
This is a video of a 3.3 pounds indoor plant :
http://www.youtube.com/watch?v=QB0W6XWOEvwOld articles but still relevant :
http://www.cannabisculture.com/articles/3268.html http://www.cannabisculture.com/articles/3368.htmlWelcome to Canada.