This invention relates to a method to correct for error in an anti-Stokes 
photoluminescence measurement in a Foerster-type 
resonance energy-transfer 
assay. The method comprises the steps of exciting anti-Stokes photoluminescent molecules, ions, phosphors, chelates, or particles, i.e. donors of the 
assay, with one 
wavelength or multiple wavelengths of light wherein the 
wavelength or wavelengths are greater than that of an emission 
wavelength of 
acceptor molecules in the 
assay; measuring emission 
light signal at a wavelength, which is the emission wavelength of the 
acceptor molecules in the Foerster-type 
resonance energy-transfer assay, and which differs from the emission wavelength of the anti-Stokes photoluminescent donor in at least two different 
time windows; a first time window within the time window defined by the excitation light pulse, i.e. within the time 
window opening when the excitation light pulse is switched on and closing when the excitation light pulse is switched off, and a second time window to follow the first time window not at all overlapping with the time window defined by the 
excitation pulse; and correcting the emission 
light signal measured, comprising signals originating from non-radiative and radiative 
energy transfer, within the first time window by estimating the ratio of the signals from non-radiative and radiative 
energy transfer or the 
signal originating from radiative 
energy transfer using at least one emission 
light signal measured in the second time window. This invention also relates to the use of a device according to the method of the invention, a 
system for carrying out the method and a 
software product for the 
system.