The Serengeti glasses model 5222C and 5222R differ primarily in their lens colors and finishes. The 5222C features a classic brown lens, which enhances contrast and depth perception, making it suitable for various lighting conditions. In contrast, the 5222R model comes with a gray lens that offers a more neutral color perception, ideal for bright sunlight. Both models offer the signature Serengeti photochromic technology, but their lens choices cater to different user preferences and environments.