Shading squash seedlings at 60% light helped them grow better and do photosynthesis more efficiently compared to 20% light and normal conditions. Seedlings with more shade had higher growth rate, better photosynthesis, and lower stress levels. They could handle less CO2 in the air and needed less light to start photosynthesis. Seedlings with more light could handle more CO2 and needed more light to start photosynthesis. Overall, squash seedlings did best with 60% light shade, showing healthier growth and photosynthesis.