Editing Xanthophyll (section)

==Occurrence==
Like other carotenoids, xanthophylls are found in highest quantity in the [[leaves]] of most green [[plants]], where they act to modulate light energy and perhaps serve as a [[non-photochemical quenching]] agent to deal with triplet [[chlorophyll]] (an excited form of chlorophyll),{{citation needed|date=June 2012}} which is overproduced at high light levels in photosynthesis. The xanthophylls found in the bodies of animals including humans, and in dietary animal products, are ultimately derived from plant sources in the diet. For example, the yellow color of chicken [[Egg (biology)|egg]] [[yolk]]s, fat, and skin comes from ingested xanthophylls—primarily [[lutein]], which is added to chicken feed for this purpose.

The yellow color of the [[macula lutea]] (literally, ''yellow spot'') in the [[retina]] of the human eye results from the presence of [[lutein]] and [[zeaxanthin]]. Again, both these specific xanthophylls require a source in the human diet to be present in the human eye. They protect the eye from ionizing light (blue and ultraviolet light), which they absorb; but xanthophylls do not function in the mechanism of sight itself as they cannot be converted to [[retinal]] (also called retinaldehyde or [[vitamin A]] aldehyde). Their physical arrangement in the macula lutea is believed to be the cause of [[Haidinger's brush#Physiological causes|Haidinger's brush]], an [[entoptic phenomenon]] that enables perception of [[polarization (waves)|polarizing]] light.