the sun may not be able to penetrate foilage or shaded areas but it does not lose its intensity like a light for every foot it loses half of its intensity.
ok if you have 140,000 lumens at 1 ft away to begin with and you lose half its intensity for every foot away the light is and at 4 ft I get 17,500 lumens in a 16 sq ft garden with a 1000 watt lamp 4 ft away that would be 1094 lumens per sq ft.
there is a link below that explains lumens and lights in more detail.
http://www.hydroempire.com/store/hyd...osynthesis.php