Male body reflectance, quantal catches for the different light treatments and irradiance of unfiltered light. Mean reflectance of (AI) the background, (AII) cheek region, (AIII) the abdominal region and (AIV) the ventral spine of male sticklebacks. (BI-BIV) Relative quantal catches calculated for the four stickleback cone classes (UV, S, M, L) affected by the reflectance of the experimental background and each male body region under fullspectrum illumination (Natural) and under the four treatment filters (UV-, SW-, MW-, LW-). Quantal catches are calculated relative to the excitation of the four cone types by the stimulus background under unfiltered light (C) Relative irradiance (log quantal flux) of the True Light tubes used in the experiment and visual modelling. Irradiance was measured with an Avantes AVS-USB2000 connected to an Avantes CC-UV/VIS cosine corrector located in the stimulus tank centre with filters removed. Irradiance calibration was performed versus an Avantes NIST traceable irradiance application standard.