Tree shape and structure with a north south row orientation more or less determine how much direct light gets to each leaf and fruit in the tree canopy. For some cultivars it means delayed harvest or multiple picking for varieties like Gala and lower volumes of premium quality fruit overall. All cultivars and strains do not respond the same to varying amounts of light getting into the orchard. Fruit have a unique way of hiding in the tree canopy even with a good summer pruning. These apples may have great seed count, good size and be full of sugars but will finish without adequate colour.
Sunlight is free of charge only to the top of the tree canopy.
The real cost comes in attempting to distribute sunlight through the canopy of the orchard. Recent technology has enabled the manufacture of reflective foils that can be laid on the orchard floor and will literally bounce back and up into the tree canopy enough light in the right wavelengths to change the concept of growing certain cultivars. The quality of this light is similar to the sunlight itself. The cost of this technology appears to be relatively low with the bulk of expense in laying and securing the material. The foil itself is a few pennies per linear foot depending on width.