Ten years of questions and nobody's answering them. First of all, the two values are not related at all, PO represents the rated luminous efficiency of the chip, which is mainly used in the white chip, because the excitation phosphor is related to the rated luminous efficiency of the chip, chip manufacturers according to customer needs, write this parameter on the label. mcd is a personal brightness unit that appears on the label of small-size chips, mainly used in chips with sizes below 14mil chips.