Electronic devices may include displays. A display may include backlight components such as a light guide plate that distributes light from a light source across the display. The light source may include a plurality of light-emitting diodes mounted on a printed circuit substrate. A portion of the light guide plate may be attached to the printed circuit substrate using adhesive. The adhesive may be a supported adhesive that includes a lining of reflective material. A reflective coating such as a layer of white coverlay may be formed on the surface of the printed circuit substrate and may be configured to reflect light into the light guide plate. The reflective coating may serve as a solder mask. The printed circuit substrate may be attached to a metal display chassis using adhesive. A shim may be used to raise the height of the light source relative to the printed circuit substrate.