How do you measure adequacy of artificial light?
I continue to have some unclarities about fluroescent light. I have recently bought Walmart's grow light which many people have given very good reviews for growing AV-s under it.
I have installed it, as shown in my other thread about light, but at the eye-level I did not feel it provides sufficient light for the plant.
I read that in order to know how much light a plant is getting at any time, you need to place a light-meter at the plant level, right where the light falls...and the meter will tell you how much ftcandles it gets.
Well...where my plant sits under WallMart's grow tube, no further away than 6-7 inches below the plant...the light level barely reaches 200ftcandles!!
I read the light output must be at least 500ftcandle to mean anything for the plant.
In that case, how come that so many people seem to grow plants successfully under such an apparently weak tube?
I have one other CFL bulb in a decorative lamp; that one seems to spread more bright light...but even under that one, when I measure the actual light level reaching the plant, it is no more than 300-400 ftcandles, with the lamp at 7-8 inches above the plant.
I did measure the light level when the window gets naturally sunny...and then I get indeed 1000 ftcandles (the "real deal" the plant seems to need).
So how do people grow AV-s under artificial lights when they seem to provide inadequate amounts of light at the recommended distances? Or is it possible that this light-meter I am using is not that good?
Thank you for any clarifications!