Some people figure out their lighting requirements using watts, some figure using lumens. Since this is a basic kind of posting I am not going to delve into PAR [used to be what we strived for in golf, go figure.
] or PGRE(plant growth radiant efficiency). If those interest you have a look at the Tazawa study
Part #1 and
part #2.
I personally figure using lumens. I add watts when I want to figure out my electricity bill.
From the
lighting section of the
grow guide :
Quote:
To determine how many lumens per square foot you have: Find out the square footage of your space. Width x Depth = Square feet. Divide the lumens available by your square footage. This will give you lumens per square foot. Example: Say your space is 3 feet deep by 4 feet wide, 12 square feet. The total lumens available from your light(s) is 45000 lumens. 45000/12 = 3750 lumens per square foot.
Now for the big question. How much light do I need? Technology has advanced so much in the last 15 years that we are constantly refining the process and updating what we know works best for growing. Current theory holds that the minimum amount of lighting needed to sustain growth is around 2000 lumens per square foot. Mid range is around 5000 lumens per square foot. Optimal is 7000-7500, or higher, lumens per square foot.
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So you can get your lumens from your bulb/tube. If you don't know it, again reference the
Lamp Lumen Data thread and look it up.
Figuring lumens one thing you have to take on faith is the manufacturers lumen claim. We are just going to use it for a base anyway. The only true way to figure out your lumens per sq. foot is to utilize a high quality light meter. Failing that, we can get a general idea using the above formula.
Once you have figured out your lumens for your grow space, keep in mind it is
theoretical. You will be losing lumens with the placement of your lamp, with your reflector and your reflective material you utilize. This is why I try to achieve 7,000 lumens per sq. ft.
minimum. Not having a light meter, I figure even if I am only getting 3,500 true lumens per sq. ft. it is above the minimum suggested in the literature. This is just my way of getting in the ballpark.
So to sum it up. Do you have enough light? Follow the formula I posted from the grow guide, if you don't have a light meter, err on the side of caution and cut it in half to be safe and you can answer your own question...
One final note: Most of what I have learned, I have learned from this site and the outstanding gardeners on these boards. If I have something wrong, it is the fault of the student and his ability to learn, not the fault of the teacher.
Good growing,
Plains