A method for the time-differentiated detection of a spectrum of a test object comprises providing a first conversion dye, which is configured to convert light with a first spectral distribution in the visible range into light with a second spectral distribution in the infrared range. The first conversion dye is excited with a light pulse in the range of the first spectral distribution during a first time period, and a light fraction, reflected or transmitted by the test object, in the range of the first spectral distribution is registered during a first time interval. During a subsequent second time period, a fraction of converted light reflected or transmitted by the test object is registered. According to the invention, the first time interval is selected so that it lies substantially inside a luminescence lifetime for the first conversion dye in the first time period.