A filter arrangement can transmit and/or reflect light emanating from a moving object so that the emanating light has time variation, and the time variation can include information about the object, such as its type. For example, emanating light from segments of a path can be transmitted/reflected through positions of a filter assembly, and the transmission functions of the positions can be sufficiently different that time variation occurs in the emanating light between segments. Or emanating light from a segment can be transmitted/reflected through a filter component in which simpler transmission functions are superimposed, so that time variation occurs in the emanating light in accordance with superposition of two simpler non-uniform transmission functions. Many filter arrangements could be used, e.g. the filter component could include the filter assembly, which can have one of the simpler non-uniform transmission functions. Time-varying waveforms from sensing results can be compared to obtain spectral differences.