I studied the the air temperature and global solar radiation at Corvallis, Oregon, and Ithaca, New York, measured on 5 minute intervals in 2014 and 2015. From those data, I calculated the effect of morning or afternoon shade.

This is the full report: Effect of simulated shade on C₃ grass at Corvallis, OR, and Ithaca, NY.

I calculated the estimated photosynthetically active radiation (PAR) if morning shade were imposed from sunrise until 2 hours before solar noon, and I called that PAR_ams. I also calculated the estimated PAR if afternoon shade was imposed from 2 hours after solar noon until sunset. I called that PAR_pms.

The L% on the y-axis in this chart -- you can read more about this in the report -- is showing the result of $100(log_e(\frac{PAR_{ams}}{PAR_{pms}}))$. This gives the relative change in PAR between morning and afternoon shade. If this L% is more than 0, the morning shade is less detrimental, and afternoon sun is more beneficial. If this L% is less than 0, the full sun all morning is more beneficial, and afternoon shade is less detrimental.