OK, biochemist.

"Why is stretch a problem?
Stretch is a problem primarily in indoor grows because it greatly reduces yield. The problem stems from the limitations of artificial light and the plant’s adaptations to low light. Stretch also produces tall plants with weak and spindly stems. The weight of the buds later in flower will require staking to avoid damage and falling over. Stretch may be a sudden problem for growers with limited ceiling height.
Light intensity vs internodal distance - Light intensity diminishes exponentially with distance under artificial light (the inverse squared law). Sunlight is not affected by distance and can penetrate deep into a canopy.
Marijuana requires high light levels to thrive and produce high yields. A plant is at its optimum flowering height when all it’s bud sites are bathed in intense light (ideally the entire plant is equally lit, producing dense bud from top to bottom).
Stretched plants are tall and their lower bud sites receive exponentially lower lumens than top colas. Budsites that are not receiving intense light will not produce well, and often the light and extra plant height is wasted. Tall plants require more energy to pump water to its leaves and transport photosynthate from its leaves. This extra energy could have gone into flowering. Stretched plants can yield 30-50% less."

I feed Foxfarm per Foxfarm schedule and from a reputable seed source.