An optical measurement instrument includes: an excitation light source (120) arranged to produce an excitation beam for at least one of samples to be measured and a detector (132) arranged to detect an emission beam emitted by one of the samples to be measured and to produce a detection signal responsive to the detected emission beam. The optical measurement instrument further includes an arrangement for controlling temperature of the samples to be measured. The arrangement includes: one or more temperature sensors (176) for producing one or more temperature signals responsive to temperature of a measurement chamber (170) of the optical measurement instrument, one or more heating resistors (171-175) arranged to warm the measurement chamber, and a controller (177) arranged to control electrical power supplied to the heating resistors on the basis of the one or more temperature signals.