"Even in the absence of a request, a trial court must instruct on general principles of law that are commonly or closely and openly connected to the facts before the court and that are necessary for the jury's understanding of the case." ( People v. Montoya (1994) 7 Cal. 4th 1027, 1047 [31 Cal. Rptr. 2d 128, 874 P.2d 903].) However, "the court is required to instruct sua sponte only on general principles which are necessary for the jury's understanding of the case. It need not instruct on specific points or special theories which might be applicable to a particular case, absent a request for such an instruction." ( People v. Owen (1991) 226 Cal. App. 3d 996, 1004-1005 [277 Cal. Rptr. 341]; 5 Witkin & Epstein, Cal. Criminal Law (2d ed. 1989) Trial, 2925, pp. 3586-3587.) Generally, the burden of requesting supplemental or clarifying instructions falls on the defendant, and failure to request such instructions waives the contention of error. ( People v. Lang (1989) 49 Cal. 3d 991, 1024 [264 Cal. Rptr. 386, 782 P.2d 627].) Here, the phrase "point source," as commonly understood, adequately conveys the statutory meaning, and thus the instructions given were a correct statement of the general principles applicable to the offense. (5 Witkin & Epstein, Cal. Criminal Law, supra, 2939, at p. 3607 ["It is not necessary to instruct jurors on the meaning of words in common usage which are presumed to be within the understanding of a person of ordinary intelligence."].) Because appellant requested no clarifying or supplementary instructions, he has waived any claim of error on this issue. Nonetheless, even if the trial court erred in failing to define "point source," this error was harmless. When the trial court erroneously fails to define a term essential to the elements of an offense, the test of prejudice is whether the error was harmless beyond a reasonable doubt. ( People v. Feinberg (1997) 51 Cal. App. 4th 1566, 1576-1577 [60 Cal. Rptr. 2d 323]; see People v. Flood (1998) 18 Cal. 4th 470, 489-491 [76 Cal. Rptr. 2d 180, 957 P.2d 869].)