Thanks to the advancement of technologies, we may be having more flexibility to determine the spectral power distribution (SPD) of light sources. Suppose any SPD is possible, we derive “extreme SPD of light source” aiming at a specific purpose such as the lowest energy, the largest color gamut, the lowest impact to fine arts, etc. We found that these SPDs always consist of multiple spikes when very high CRI is not required while the SPD of the black body radiation is continuous in wavelength. In order to investigate the effect of such light sources to human visual system and camera system, we employ two types of such light sources, namely Maximum White Luminous Efficacy of Radiation (MWLER), which gives the best energy efficiency, and Maximum Gamut Area (MGA), which gives the largest color gamut size. Both MWLER and MGA are composed of multiple spikes in wavelength. We generate such SPDs with respect to 6 types of existing light sources with same CCT and CRI (if applicable), and evaluate how sensitive these are with 10 sets of color matching functions (CMFs) given by Stiles and Burch as human visual system and 4 sets of digital camera sensitivities by computer simulation. We presume a color matrix of color conversion for CMFs and camera is adjusted minimizing errors with a Macbeth Color Checker under black body radiation with the white point constraint. With this assumption, we evaluate colorimetric error under the two extreme SPDs in addition to black body radiation and existing light sources. We find that cameras give large error (more than 20 in ΔE*_ab) for these spiky light sources which may not be accepted by users even when they are in a tolerable error range for the human visual system. It is concluded that such spiky light source could be used without problem for a variation of CMFs, but it would be problematic for color reproduction of cameras.