# `Color.UnknownIlluminantError`

Raised when an illuminant atom is not recognised by
`Color.Tristimulus`.

Has fields:

* `:illuminant` — the offending value.

* `:observer_angle` — the observer angle (`2` or `10`), if known.

* `:valid` — the list of valid illuminant atoms, when supplied.

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*Consult [api-reference.md](api-reference.md) for complete listing*