How Many Lumens are Needed to Grow Weed, Using CFL Lighting?



When it comes to CFL lighting, “the more, the merrier!”

The sun puts out roughly 100,000 lumens per sq. ft on a sunny day.

Plants grown outdoors are not harmed by the sheer amount of lumens that the sun gives off, are they?!

Plants can and do suffer stress as a result of the sun’s intense heat, but they “process” the rays as they come!

In an indoor growing environment, we want to supply all the lumens that the sun can provide (within reason), but without the damaging effects of the HEAT.


So how many lumens are needed to grow weed with CFL lighting? 

According to Jorge Cervantes’s, “Horticulture The Indoor Outdoor Medical Growers Bible,” page #208 notes details recommending the “maximum light requirement for plants.” Briefly paraphrasing an excerpt for a flowering plant’s needs:


Vegetative – 27,000 Lumens maximum
Flowering – 107,500 Lumens maximum


Let’s use those figures as a reference only, not as the “end-all” of quotes. 100,000 lumens is a good target for flowering, hence the use of 600 Watt and/or 1,000 Watt HPS lighting, to throw as much lux as possible onto the plant’s leaves, which will in turn feed the processes used by the plant to grow the bulkiest, smelliest, frostiest bud you can get your hands on.


Another common figure to use is 5,000 lumens per square foot will give you decent results, and if you can go 7,000 lumens per square foot your results will improve. 10,000 lumens per square foot may give you even better results, but it’s also possible to notice diminishing returns after this point.


However, that all depends on various factors which can’t be predicted here or  anywhere else. It just takes experience more than anything else. So again; how many lumens of are needed to grow the dankest happy hay on your side of the bay?

You already know the answer!


By Robert Narley