What is the legal test for instructing a jury on a particular defense?

Trial courts have a limited duty to instruct, sua sponte, on particular defenses. (People v. Barton (1995) 12 Cal.4th 186, 195.) That duty arises "'only if it appears that the defendant is relying on such a defense, or if there is substantial evidence supportive of

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such a defense and the defense is not inconsistent with the defendant's theory of the case.' [Citations.]" (Ibid.) "'Substantial evidence' in this specific context is defined as evidence which is 'sufficient to "deserve consideration by the jury, i.e., 'evidence from which a jury composed of reasonable men could have concluded'" that the particular facts underlying the instruction did exist.' [Citations.]" (People v. Burnham (1986) 176 Cal.App.3d 1134, 1139.)