I'm wanting to know how light meters (spot meters in particular) work. Not how to use them, but the actual electronic bits! I'm thinking about the kind of details that would enable me to build one from scratch using off-the-shelf components. Obviously I'd get a much more accurate and more reliable meter if I just bought one, but like learning about lens design I'm interested in it even if I never actually go out and try it. Things like what kind of light-sensitive parts do they use, how does that get converted to an exposure value, and how do they limit the measurement angle to one degree without an extremely long focal length lens? This may be too complicated to answer in a forum post so if someone could direct me to appropriate resources that would be great!