What are the main differences between lenses with an aperture of f/1.8 and f/1.4, and how do these differences impact photography?

Lenses with an aperture of f/1.8 allow less light in compared to f/1.4 lenses. The main difference is the amount of light that can enter the lens, affecting the depth of field and low-light performance in Photography. A wider aperture like f/1.4 creates a shallower depth of field and better low-light capabilities, making it ideal for portraits and low-light situations.