Hi Gary, You said: “Also my G/F has
blankets on her horse all winter, I can't see the lights going through
those to stunt the hair growth.”
Hair growth is affected by lights via the Pineal gland in the brain.
Thus, Light gets to the pineal gland via the optic nerve (the eyes), not the hair
follicles themselves, So you can cover up all the hair follicles with a blanket,
& still get the effect, because the horse’s eyes receive the light to
affect the Pineal. HTH