> IIRC, lambda is wavelength.

Correct, Leeneia. My son also informed me that capital-lambda is the symbol for the video game Half-Life (apparently because radioactive decay turns up in the first few sentences of the back story); this reminded me in turn that Lambda-CDM is the name of the (current) standard cosmological model in physics .... though in our house, it stands for the half-life of Cadbury's Dairy Milk in the fridge.