Cold-hardening sweet pepper leaves at a cooler temperature improved their ability to withstand cold temperatures. The researchers studied how photosynthesis was affected by low temperatures in both hardened and unhardened leaves. They found that while cold temperatures decreased photosynthesis in all leaves, hardened leaves were better at using light energy and maintaining photosynthesis efficiency. Hardened leaves also showed less photoinhibition, or damage from excess light, compared to unhardened leaves. Overall, cold-hardening improved the resistance of sweet pepper leaves to cold-induced photoinhibition, especially in cold-tolerant varieties.