Disclosed is an apparatus and method for a compact, rugged, and inexpensive spectrometer that will make possible a range of new applications for optical spectroscopy including point-of-care medical devices, personal monitors, and ubiquitous environmental sensing. Embodiments of the disclosure include silicon photodetectors where incident light passes through a layer of an inexpensive, absorbing thin film. In one embodiment, one or more photodetectors may be used where a series of absorbing thin film layers are passed over the photodetectors. In another embodiment, an absorbing thin film layer is placed over one or more photodetectors where the absorptivity of the thin film layer is different for each photodetector.