If crown cropping gave it only a part of the crown an uncropped Tree would have, its growth rate is limited by that factor. The circles drawn on the screen are the cropped crowns. The dots in the middle of the circles are the trunks. Next, every 5th year, the Trees compete for light. Neighboring Trees whose crowns are within 45 degrees of straight overhead are capable of reducing light input at this Tree's crown.
Light is calculated at crown top.
The Tree goes through all candidate neighbors and asks for their shadows at this Tree's height. Shadows have shape and lightness. The shape is crossed with the current Tree's crown area for overlap. Each Tree species has a parameter lightCoeff which says how much light filters through their crowns. A Hemlock casts a dark shadow, with only 6 percent of daylight eeking through.