Sunlight reaching your windows arrives as visible light, ultraviolet and infrared energy. The infrared portion is invisible but is a significant part of what you feel as heat inside the car, which is why darkness alone is not a reliable guide to how a film performs. Kepler's nano-ceramic IR and IR+ films are engineered around the infrared part of the spectrum, so solar performance comes from the ceramic construction rather than simply from a darker shade. That's a real advantage on a Tesla, where you may want lighter film on some glass. Because visible light transmission and solar heat performance are measured separately, compare the exact film and shade you're considering, and ask your dealer for the data sheet on that product.