The spectra of these illuminants are published in Publication 15&colon;2004. The corresponding whitepoint values for and can then be inferred using the standard illuminants. Various attempts were made to enrich BWG with illuminants from gas oil in the 1860s. The F series of illuminants represent various types of fluorescent lighting. Illuminants B and C are easily achieved daylight simulations. For example, one of the simplest illuminants is the "E" or "Equal Energy" spectrum. The chromaticity coordinates of the Illuminants D are said to form the "CIE Daylight Locus". Publication 15&colon;2018 introduces new illuminants for different LED types with CCTs ranging from approx. Light sources and illuminants may be characterized by their spectral power distribution (SPD). Standard illuminants provide a basis for comparing images or colors recorded under different lighting.