Much light in architectural spaces is absorbed by objects and never perceived by occupants. The colour appearance of objects illuminated by light spectra that minimized this absorption was determined. Colour differences were calculated for 15 reflective samples when illuminated by various coloured test light sources and reference white illuminants. Coloured test spectral power distributionos (SPDs) can reduce energy consumption by up to 44% while maintaining identical colour appearance of illuminated objects. Energy consumption can be reduced further, but with noticeable colour shifts. Results quantify the trade-off between colour fidelity and energy consumption with this approach.