Charles Ellicott Commentary 1 Chronicles 28:15

"by weight also for the candlesticks of gold, and for the lamps thereof, of gold, by weight for every candlestick and for the lamps thereof; and for the candlesticks of silver, [silver] by weight for [every] candlestick and for the lamps thereof, according to the use of every candlestick;" — 1 Chronicles 28:15 (ASV)

Even the weight for the candlesticks of gold. —Rather, and a (specified) weight for the golden lampstands, and their golden lamps, in the weight of each lampstand and its lamps; and (a weight) for the lampstands of silver by weight, for a lampstand and its lamps, according to the service of each lampstand.

The meaning still is that David gave Solomon a description of the designated articles, fixing the proper weight for each. (Compare to Exodus 25:31 and following, the great golden candelabrum of the Mosaic sanctuary.)

No mention of the silver lampstands occurs anywhere else in the Old Testament. According to the Rabbis, they stood in the chambers of the priests.