The present disclosure proposes an improved apparatus and method for counting of sea lice by providing a stable and controlled light environment which ensures counting of sea lice reliably and independent of weather conditions and an optimized spectral power distribution and intensity of the light for improved observation (detectability) of sea lice with respect to fish skin. An embodiment of the disclosed light system comprises multiple LEDs, at least two LEDs providing a light colour with peaks in the range 490-540 nm (Cyan/Green) respectively 620-660 nm (Red).