A time-resolved fluorescence system comprising: a light source; a light detector; a sample holder disposed between the light source and light detector; a motor; a light transmission modulator disposed around the sample holder and comprising a pair of plates (106, 107) attached to the motor for rotation about a common axis, the pair of plates (106, 107) arranged to allow transmission from the light source to the sample holder in a first rotated position, to allow transmission from the sample holder to the light detector in a second rotated position and to block direct light transmission between the light source and light detector in both first and second rotated positions; and characterised by: a computer system connected and configured to operate the motor to rotate the light transmission modulator, to operate the light source to illuminate the sample holder when the light transmission modulator is in the first rotated position and to capture light signal data from the light detector indicative of fluorescence of a sample in the sample holder, wherein the computer system is configured to stop operation of the motor once the light transmission modulator is rotating and to capture light signal data from the light detector after stopping operation of the motor and while the light transmission modulator is rotating. a light source; a light detector; a sample holder disposed between the light source and light detector; a motor; a light transmission modulator disposed around the sample holder and comprising a pair of plates (106, 107) attached to the motor for rotation about a common axis, the pair of plates (106, 107) arranged to allow transmission from the light source to the sample holder in a first rotated position, to allow transmission from the sample holder to the light detector in a second rotated position and to block direct light transmission between the light source and light detector in both first and second rotated positions; and characterised by: a computer system connected and configured to operate the motor to rotate the light transmission modulator, to operate the light source to illuminate the sample holder when the light transmission modulator is in the first rotated position and to capture light signal data from the light detector indicative of fluorescence of a sample in the sample holder, wherein the computer system is configured to stop operation of the motor once the light transmission modulator is rotating and to capture light signal data from the light detector after stopping operation of the motor and while the light transmission modulator is rotating. a computer system connected and configured to operate the motor to rotate the light transmission modulator, to operate the light source to illuminate the sample holder when the light transmission modulator is in the first rotated position and to capture light signal data from the light detector indicative of fluorescence of a sample in the sample holder, wherein the computer system is configured to stop operation of the motor once the light transmission modulator is rotating and to capture light signal data from the light detector after stopping operation of the motor and while the light transmission modulator is rotating.