A vertical-type backlight unit for flat panel display apparatuses. The vertical-type backlight unit includes a plurality of lamps installed in a housing in substantially parallel manner. A plurality of reflection plates are combined with corresponding lamps to constitute independent lamp module cartridges, each of which is removable from one side of the housing. A diffusing pad/plate is disposed over the plurality of lamp module cartridges for diffusing light. An optical sheet is optionally provided on the diffusing pad/plate.