Many modern copiers and laser printers now charge the photoconductor drum with an electrically conductive roller, reducing undesirable indoor ozone pollution.
As no light would reflect from the black marks on the paper, those areas would remain charged on the photoconductor, and would therefore retain the fine powder.
Even though laser print is a full-page technology, with each page built up on a photoconductor drum, it's still not as fast as a full-width inkjet head.
