ISO 3664 species that in the imaging industry – graphic arts, photography, and graphic design – 5000K lighting, a.k.a. D5000 or D50 as it is commonly referred to, is the best light source to use. It has equal amounts of Red, Green, and Blue light energy, so it will not accentuate or subdue any colors. In imaging applications, many colors are viewed at the same time (e.g. a photograph), so all colors need to be represented evenly. This is why an equal energy light source is so important to this application.
D5000 should be the primary source, but a secondary source can also be used. In packaging applications, using the source used in the store would be useful. This is typically a high efficiency fluorescent lamp.
Old color evaluation booths also offered 7500K lighting. This light source was only used to help the pressman see the yellow ink on the press sheet. This was dropped from the standard (ISO 3664) over ten years ago. D50 is the only ISO standardized source now used in the imaging industry.