Preferred illumination for paintings: Cool–warm balanced colour temperature predicted from radiometry and colorimetry

Major factors to be considered when designing lighting for paintings include colour discrimination, colour diversity, clarity and the balance of cool–warm (bluish-yellowish) lighting. This paper concerns the last factor and presents two radiometric and one colorimetric methods of predicting cool–warm balanced illuminants. For a high correlated colour temperature, the spectral power distributions of Planckian and daylight-simulating illuminants are high in short wavelengths and low in long wavelengths and, therefore, appear bluish. The reverse is true for low correlated colour temperature illuminants, which appear yellowish. The balanced spectral power distribution occurs at 5000 K. MacAdam’s complementary powers function is psychophysical and represents the power of wavelengths across the visible spectrum required to neutralize (convert to white) their complementaries. Again the balanced power occurs for illuminants of 5000 K. Hence, a correlated colour temperature in the 4500–5500 K range is recommended for cool–warm balanced illuminants. This recommendation is supported by results of four recent experimental studies.