Retinal
chemical compound
Retinal (also known as retinaldehyde) is a polyene chromophore. It binds to opsin proteins and forms the chemical basis of visual phototransduction, the light-detection stage of visual perception (vision).
Some microorganisms use retinal to convert light into metabolic energy. One study suggests that approximately three billion years ago, most living organisms on Earth used retinal, rather than chlorophyll, to convert sunlight into energy. Because retinal absorbs mostly green light and transmits purple light, this gave rise to the Purple Earth hypothesis.
Retinal itself is considered to be a form of vitamin A when eaten by an animal. There are many forms of vitamin A, all of which are converted to retinal, which cannot be made without them. The number of different molecules that can be converted to retinal varies from species to species. Retinal was originally called retinene, and was renamed after it was discovered to be vitamin A aldehyde.
Vertebrate animals ingest retinal directly from meat, or they produce retinal from carotenoids – either from α-carotene or β-carotene – both of which are carotenes.
The public source identifies “Retinal” as chemical compound. This brief keeps that definition visible, then builds a research path around Retinal, chemical and compound.
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Stable identifiers, scientific names and standards terminology offer the best bridge between this overview and specialist evidence. The source revision retrieved here is dated Aug 23, 2026. The linked authority identifier is Q422001. The Library of Congress control number is sh85113331. None of the 1 selected statements returned an explicit reference.
A general summary may omit uncertainty, sample limits or methodological disagreement that is explicit in the technical record. The source lead contains qualifying language; that uncertainty should survive quotation, summary and reuse. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Retinal” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.