The spectrometer may comprise a plurality of semiconductor nanocrystals. Distinct from a wavelength of the spectrometer may be achieved by different light absorption and emission characteristics of different populations of semiconductor nanocrystals (e.g., different materials, size, or populations of both). Spectrometer therefore can operate without the need of a grid, Prim algorithm, or oil phase one optical component. UV exposure is a personal tracking device comprises a semiconductor nanocrystal spectrometer to record exposure to a portable, tough, and inexpensive, and the user's UV radiation. Other applications include a personal device with a (e.g., smart phone) or a semiconductor nanocrystal spectrometer introducing medical devices.