This paper examines the difficulties inherent in producing, as a physical reality, light of the correct spectral power distribution to comply with theoretical daylight standards, notably the Commission Internationale d'Eclairage (CIE) standards D55, D65, and D75. The methods available for filtering xenon arc, tungsten, tungsten halogen, and fluorescent lamps to emulate daylight standards are compared. Only two of the daylight simulators assessed are considered to provide light sufficiently close to that defined by the theoretical standards as to exclude the possibility of metamerism.