This term is commonly misused, describing a color that changes according to the light. It is actually the property of two colors, which appear to match under one light source, but which are dissimilar under another.
Perceived lightness. It is totally relative. It has nothing to do with how much candlepower there is, but rather, how we adjust the range of brightness. Humans are most comfortable in a narrow range of luminance.
From The Donald Kaufman Website Glossary