Samsung Electro-Mechanics, a Samsung Group affiliate that manufactures electronic components primarily for cellular telephones, said yesterday it would begin mass production early next year of two new lines: light-emitting diodes powerful enough to be used in traditional lighting applications, and backlight units for notebook computers and other display screens. Samsung said it would produce several different models of its new backlighting unit, including a seven-inch backlight for use in navigation systems, a 12.1-inch model for laptop computer screens and a 24-inch model for backlighting desktop liquid crystal display monitors. The largest application would be a backlight unit for a 40-inch television display.